text:
Is this model feasible to print?
I have a 3D model that I'd like to print. This is my first project, so I'm trying to decide if I'm getting in over my head. Here's the model rendered with Blender:

If I throw it at a commercial printing shoppe, is it going to be fairly straight forward? Or is it unlikely to be able to get the colours fitting together like this to work well?

Hi, @ajwood! I'm not fully understanding how your model works; are all those colored sections supposed to be printed individually, or printed as a whole?

@TormodHaugene I actually don't really care, as long as it looks like this in the end. I assume I have a fair bit of work to do to the meshes before they're printable; they're separate objects right now, but I could merge them if necessary.

The answer to your question, 'can this be printed', is dependent upon a few more factors on your end, such as: Do you want the various colors to be printed as shown, together as one piece or multiple pieces put together? How much are you willing to spend, what size is the model, and what is your desired roughness/for the finished product? Which online printing shop, in particular?

A lot of people at the hobbyist level work with FDM (rolls of plastic) printers. This would be a challenging print to print directly via FDM in color. You will see this bias in the answers.  Not many people in the hobby have access to 'Full Color' printers. This can be printed in color, but you likely won't have the vibrant colors displayed here, more of a pastel version of them. This is an excellent example of something certain types of 3d printers can produce easily.

Here is a set of options you can get:

print the object on multi color printer

Unfortunately we got some limitations here (on the market). Printers have limited set of heads which are in fact printing in one color at a time. So we usually have 2 colors, there are also 4 color heads. If there are more then they are rare, expensive or rare and expensive.
here are examples of such color printouts:
project
project

print object splitted

In this case you can have single color printer. You print parts in one color then you change filament and print other color and so on. The issue here is to have well formed object which is designed for such print method (it's connectable in some way) or you can stick printed parts with the glue.
here are examples of such puzzled printouts:
project
project

print and paint

here are examples of such painted printouts:
project
project
NOTE:
All above assumes that you are gonna print your object in FDM technology. You can also take a look on other technologies such as:

Stereolithography(SLA)
Digital Light Processing(DLP)
Selective Laser Sintering (SLS)
Selective laser melting (SLM)
Electronic Beam Melting (EBM)
Laminated object manufacturing (LOM)

Getting this printed at a professional print shop will be quite straightforward, given that you prepare the model nicely for printing (i.e. make it a watertight, manifold mesh).
You could print the pieces separately and assemble them later. You might also look in to getting this printed in one piece with the colors already in place on a ProJet machine, which is available as "Full Color Sandstone" on Shapeways. This might be a nice option for you.
With regards to printing the pieces separately you could go with pretty much any printing process, bearing in mind that FDM will offer the greatest range of available colors but the worst surface finish. You could try SLS instead (White Strong&Flexible on Shapeways) which is a white material that can be dyed with fabric dyes (such as RIT and Dylon) to achieve any desired color. Of course, anything you get printed (regardless of the material) could also be painted.
If you decide to get this made in FDM then make sure to choose a nice orientation for the pieces (minimizing overhangs) so you get the best quality possible. The print shop may be able to help you with this.
Getting the parts to fit together will not be a problem if you keep a little bit of clearance (around 0.2-0.5mm) between parts that interlock.

You would need to ask around shops to see what they think about this 3d file. What I have heard is that colors of prints end up blended together, and that the print resolution is low. How many colors are you using? You could probably get a quality print, but it would come with a high price. Print quality is dependent on the expensiveness of the machine used.

I could imagine printing multiple pieces and assembling them. Would that be a factor to consider?

the other guy wins.

The simplest and cheapest method to have this object printed would be to have individual STL files for each part and give these to the print shop with the color of each piece.
Printing as a single piece would be much more expensive as more advance methods would be needed as mentioned in the other answers.


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How could I keep the material on the print plate from bending up on a makerbot 2?
I printed a big base for a model, but the corners of the bottom bent up, making the whole base rock when set on a table. Is there a quick fix for a makerbot2 without a heated plate?

Consider using a different material. Since you're on a replicator 2 you're probably not printing with ABS (which would be a terrible choice for a large, flat model) but probably with PLA. Perhaps you could try printing with PET(G) instead, which tends to warp even less.
You could try modifying your model a little. If you include several grooves in the bottom surface of your model that may provide some "strain relief" so-to-speak, preventing warping.
Increase adhesion: print your initial layer slower, closer to the build surface, at a higher temperature, with a brim, and with some kind of print surface to increase adhesion (tape/glue/hairspray).
Increase ambient temperature. The Replicator 2 does not have a heated bed, but you could still make the cooling more gradual by enclosing the printer, shielding it from drafts, etc...

Try printing with a raft, and adding "helper discs" to expand the size of the raft. You might also try lowering your extruder temperature a bit to reduce the cooling temperature differential.

here are the options:

Use brim settings which increase contact surface.
Use some sort of glue. People are using many things including hairspray. I do prefer paper glue stick.

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SLS 3D printer to DMLS 3D printer
I know that the SLS 3D printer stands for selective laser sintering,where as DMLS stands for direct metal laser sintering.
I want to know that,can i convert SLS 3D printer to DMLS.
By just changing powder(or another way?)

By just changing powder: No.
Changing the powder, the laser and the chamber, maybe you can get something, but it's not recommended.
DMLS machines use a sealed chamber with a flow of Argon, Nitrogen, or other gas to prevent oxidation of metal powder (and avoid fire or explosions).
Laser power for metal needs to be of higher power than that used por polymer laser sintering (SLS, SLM, LS, etc).
BTW. DMLS also need a metallic build plate to dissipate heat.

Totally agreed with the answer provided.To add to that answer, the use of DMLS lies on the thickness and material limitations of SLS method. So, regarding the amount of thickness, the original source of sizing for both the methods vary drastically and hence cannot be inter-converted.

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Do 3D Printers Prefer Particular Topology?
Do 3D printers prefer particular topology?  In case I'm not using the word quite right, I'm specifically wondering if I should make the faces in my models:

triangles
quads
n-gons..

The most common file format in 3D printing is STL. This file format is using triangles only so when you export an object from your CAD application to STL then exporter has to transform all n-gon faces into triangles.
Once the file is created then it is usually imported by slicer application (or module) which performs slicing using polynomial calculation to find intersection with next surfaces. Here is good example of such intersection finding in javascript.
So answering your question:

no - it doesn't matter as you usually use file format in which faces are triangles but
yes - it matters as all your n-gon faces needs to be transformed into triangles


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Offset in X or Y axis
How can I set an offset in y or x axis so that I can move the position of my printed object. I have tried doing this with so many options in Repetier, and in Slic3r, and still nothing, please, have you got any ideas?
First Edit:
I have added an image of the changes I have done, nothing of this works for me

In Repetier right click and drag moves the object. Is it working for you?

There are two things which shouldn't be mixed.

Position of the object relative to its own coordinate system.

In general object doesn't have specific position stored inside. Which is obvious as structure of the object should store construction of an object but not its position. So position is relation-to-something so to speak and because object itself doesn't contain any information about object environment then there is no position stored.
But there is one hack. All coordinates stored inside object are in fact a realtion to some starting point. Let's say it's a zero-point or starting point of the coordinate system of the object. This is sometimes anoying because it's usually bottom left corner or center of the object. Unfortunately some applications store this starting point out of the object. This means that object has starting point in some point but this point is outside of the object itself.
This cause the situation when user loads an object in another application then object is translated in "strange" position.

Position of the object in printing application.

When user loads an object into printing application then object is usualy set in the center of build plate. This also sounds obvious but if inner coordinate system of the object is translated then object can be repositioned even out of the build plate.
So what is the solution for such situation.
There are two options.

Manage object coordinate system in the application which create STL file  or convert object into STL format or
Manage (switch off) option called "center on build plate" or "center on the bed" or "center object" or "auto-center parts" in printing application.

Then it will be possible (or easier) to position object according to user needs.
Another issue is STL object which is in fact kinda assembly of separate objects. If you encounter such situation. See here for example

These two guys are stored in one STL file so they have common coordinate system and common starting point. All above applies to such assembly.
Applications allows user to split such assembly into separate objects so each one can be repositioned separately. But be careful - split can disassemble parts of the object itself. In the example the tounge of the trex is 3rd object in the assembly.
In terms of mentioned aps:

Reptier: go to object placement "tab" and set position manually
Slic3r: go to Printer settings and set "print center", also you can switch off File > Preferences > Auto-center parts
MetterControl: go to printer > print area and set print center

I don't see that option, I have add an image of my configuration of Repetier host and Slic3r. I have tried something similar of what you say, but is not working for a strange reason

@Delfin File > Preferences > Auto-center parts

@Delfin i just realized that your screen comes from Repetier so you should rather go Config > Preferences > Object placement > Auto position object...


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Is inconsistent vertex density a bad thing?
Will an inconsistent vertex density likely introduce artifacts in a print?  Or is it OK as long as it's a smooth surface?

No it's not. Take a look here for little explanation how slicer works http://3dprinting.stackexchange.com/questions/1180/do-3d-printers-prefer-particular-topology

The link refers to triangles as opposed to other polygon shapes in a model. This model has all triangles, so I'm not sure I see the pertinence to the question. This image shows all triangles, so my educated guess is that it would print fine. We don't see the triangles of a model when printing, only layer lines, unless the model is a low-poly design.

@fred_dot_u the link gives a little explanation on how slicer works. It was assumed that the problem expressed in the question is so small (especially in the red rect) that such little explanation would be enough. Fortunately Ryan Carlyle described it in high level of details.

Based on the small size of the area in question and the not small size of the clarification answer, I'd expect that the result is trivial in terms of the slicer and/or the printer. Of course, there's no scale with which to base the model size. A 50 mm diameter sphere would probably show nothing, but a 5 m sphere might present the artifact nicely.

For the most part, the exact level of vertex density doesn't matter too much. But it does depend on the slicer and settings. Some slicers (like Slic3r) will auto-decimate toolpaths to ensure that the rate of motion commands isn't too difficult for the old, slow 8bit processors in most consumer/hobbyist 3d printers. Having a large number of very small motion commands can bog down these motion controllers and cause pause-stuttering that creates little zits on the print. Most slicers simply reduce model detail level to safeguard the motion controller. Because the contours are decimated to a minimum motion segment length, very small model triangles are irrelevant to printer performance. At the most, they might add a marginal amount of slicing time.
On the other hand, some slicers (like Simplify3d) assume you have the correct level of detail you want in your model, and will pretty faithfully reproduce the model file's contours in the sliced toolpath. If your entire model is very high mesh density / poly count in general, or if your high-density mesh regions are crossed by a layer slice, this can produce a series of very, very short motion commands. Sometimes the motion commands are even smaller than the motion resolution of the printer, and simply take up processor time (to evaluate and drop from the queue) with no benefit to print fidelity.
In a more general sense, high-poly models are dramatically more difficult for the 3d printer to reproduce accurately. There are two big issues:

Each motion segment requires some processor time to read/receive, parse, and execute. But the shorter the segment lengths are, the faster the printer runs through them. A short move takes little time to perform but still has the same processor load as a long move. At a certain point, the processor can't keep up, and performance suffers. The printer may run out of queued moves to execute and pause in place, or it may violate acceleration limits and violently clunk through corners (or even lose position) because it didn't have enough time to iterate through the calculations that determine how fast it should move.
The algorithms used by most consumer/hobbyist 3d printer firmwares (Marlin, Repetier, Sailfish, Smoothieware, etc) are based on GRBL. And without getting into the math, GRBL uses the sharpness of the corners between motion segments to decide how fast to travel through the corner. So a 90 degree turn will trigger a considerable slowdown, while a series of small angles (such as many small segments comprising a curved surface) is not recognized by the algorithm, and it will try to barrel through the curve at full speed. On long, gentle curves, this is fine, but high-poly tight curves (such as a filleted edge or organic model detail) are traversed far too fast because no slowdowns are triggered. This means high-poly models must be printed at much lower feedrates / target speeds, because the acceleration algorithm can't figure out when to go fast or slow. Whereas a blocky, low-poly model can be printed much faster and the acceleration code will speed up and slow down as needed for good quality.

These are primarily issues with high vertex density versus low vertex density, not variable density. Small pockets of high detail are usually not problematic, as long as they are small enough that the motion planner queue (say, 16 segments) doesn't get filled with too many very small movements. A few small segments in a row is ok, but a few dozen is not.
These are limitations baked into the algorithms used by today's slicers and motion controllers. In the future, they may not be so problematic.

This is a very nice answer. It is quite surprising to me that S3D does not have decimation built-in.

It does annoy a lot of people, particularly Smoothieware users, due to a freeze/hang bug that can be triggered by very small motion commands. S3D gcode needs to be scrubbed through a post-processor script to be reliable on Smoothieboards. It does make some sense in context though when you consider that S3D DOES have a built-in manual mesh decimation tool, and is very often used with firmwares like Sailfish that already include post-processors that drop motions smaller than one motor step.


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Hatch Distance and Scan Distance
I am going through some of the basics about one of the 3D printing techniques - Selective Laser Sintering, and I am confused between the above mentioned parameters - scan distance and hatch distance. Are they the same ?
How do we calculate the value - the overlapped area of two parallel scan lines in linear scanning technique. There must be some area of overlapping for the selective laser sintering to work.
Any idea ?

Scan spacing

Within each of the ‘islands’, simple alternating scan vectors are used with the spacing between these vectors defined as the ‘scan spacing’ and the speed with which the laser spot moves across the surface defined as the ‘scan speed’.

Source

The influence of the laser scan strategy on grain structure and cracking behaviour in SLM powder-bed fabricated nickel superalloy
chapter: 2.2. SLM processing and laser scan strategy

Hatch distance

The stripe pattern is a band defined by the scan vector width (ie stripe width), the hatching space between adjacent tracks and the scan direction as well as the overlap with the neighbouring stripes

Source

Scanning patterns in SLM

Notes

The computer controlled laser scans the surface of the bed to selectively melt the current two-dimensional slice of the CAD file.
The laser scanning remelts some of the previously built layer to ensure good bonding between layers and a fully dense component overall.
Cool printing image


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'Sine wave' deviation in X-Axis on moving bed printer.
I've built a a PrintrBot inspired printer with a moving printbed for the X-Axis movement. It's controlled by a RAMPS board running Marlin firmware. And there is a problem with the X-Axis positioning.

As can be seen in the image the X-Axis is not really stable. The blocks should be 10x10x10 mm, and the top and bottom are perfect. The waving does not appear in the Y-direction, it's only in the direction of the bed movement.
Each block was printed at different speed, from medium to dead-slow. I limited the acceleration and in the last block I also limited the non-printing speed so the bed would never experience a higher acceleration than with the printing itself. But the wave effect remains. And it's also remarkably repeatable so it looks more like a synchronisation error somewhere. Does anyone has a clue, or experienced a similar effect ?

Welcome, @CeesMeijer! If you try to move the bed manually along the x-axis, does it have any slack or "deadzone"? (Deadzone would be the distance the motor has to move before the bed starts moving too.)

@TormodHaugene slack you've mentioned would rather cause irregularity or pseudo-regular changes but layer by layer. He mentioned that entities on the picture comes from different printouts, this suggests that these are not irregularities and also not pseudo-regularities, these are regular repeatable changes so they have to be caused by repeatable cause. What do you think?

flag
@TormodHaugene : There is absolutely no 'deadzone' in the bed movement. I've checked this thoroughly, because that was my first idea as well.

@CeesMeijer - it is not the bed that is moving to erroneous positions, it is the printhead being angularly offset to the left or right.  It looks like you probably have one of those 2mm spacing x 4 start screws that advances 8mm per rotation, which matches the vertical period of the error it introduces as an apparent eccentricity or bend in it puts a torque on the Z assembly that introduces this cyclic left-right error in the location of the printhead relative to the rest of the machine.  If you print something very long in Y you may find the error greater at one end than the other.

This is the issue of your z-axis rather than x- or y-axis because printing speed doesn't have any influence on the results.
I bet:

your threded rods are bent or
nuts on these rods have too high clearance or
nuts on these rods have eccentricity or
couplings (between motor and threded rods) are bent or
these couplings are badly fitted

All above suggestions concern z-axis.
[edit] because it's PrintBot its z-axis has the following disadvantage

None of these apply.. The way the printer was built makes it almost impossible for any eccentricity in the threaded rod (it's only one) to pass through to the printhead (you can see what I mean in if you look at the 'Printrbot simple). Also the movement is only on the X-Axis. I know this is not really clear from the picture but actually the front and back of the cube are quite smooth.

@CeesMeijer I've looked at PB simple. Now I'm almost absolutely sure that one of my suggestions plays a role. PB simple is stiff enough in y-axis as it has 2 rods (so printer cannot swing in front-back direction) but left-right it really can. You can check it without actually printing - If I were you I'd check with the right angle (angle gauge) while moving in z-axis layer by layer. According to your picture the deviation is about +-1mm so you will be able to check it by eye.

@CeesMeijer see edit

You're absolutely right, and I was horribly wrong... After multiple attempts to solve the problem in by tuning the motor drive, this is exactly what I found. The motor of the Z-Axis is not correctly aligned and therefore the threaded rod makes the the movement as you illustrated. thank you very much for your help.

@CeesMeijer you are welcome! Good to hear you've solved your problem


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Smooth finish in Slic3r using Support Material
How can I obtain a smooth finish like the one in this video: Easy and clean support material removal from 3D printed part., using Slic3r instead of Simplify3D? What settings do I need to change?

I'd say the clue is the material itself and the geometry of the object. But in terms of Slic3r settings you could experiment with:
(print settings >> support material)

pattern spacing (he has here something around 5mm)
pattern (I'd say the best for you is rectlinear)
contact z distance (choose 0.2 or close to that)
interface layers (here 0 (zero) for sure)
don't support bridges (this one depends on your geometry and if slic3r calculates something as a bridge or not)

All above is also connected (in a way) with HE temperature and layer height. Usualy the higher temperature (in a range for specific material) the better sticking between layers.


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Cleaning E3D hotend and tuning with Cura?
I just received my E3D v6 hotend and I am installing it on the open source design of a Prusa i3. How do I clean my hotend after each print and after using different filaments?

Usually there is no need to clean the hotend, as filament sticks well to itself rather than to the inside of the hotend. If there are remains - the simplest way to clean it up is to extrude 5-10 cm of new filament, which will gather all remainings clean the hotend.
The above concerns changing filament in the same group of plastic. So if you print PLA you can switch colors/manufacturers and so on without issues. The same goes for ABS.
There is also usually no problem when switching from PLA to ABS.
The worst scenario is to switch from ABS to PLA. This is because the extruding temperature of these two materials is different. Unfortunately ABS can have such a high melting temperature that the PLA will burn. So having a dirty hotend with ABS remainings, there is no way to extrude PLA to clean the hotend because the PLA temperature will not result in melting ABS. It can eventually lead to total plug of HE.
So what can you do when you are in such a situation (ABS -> PLA)?
You can clean the hotend first with ABS. Extrude some, wait until it is cold, ease the springs and pull or tear out the filament from the hotend.
If you are stuck you can use special drills to clean the nozzle.
But to totally omit the issue you can have two hotends :) One for ABS and one for PLA ;) But I think you can manage cleaning if you apply what I've written above.

You are overstating the issue of switching from ABS to PLA quite a bit. I find it works fine to heat my hotend up slightly hotter than I would normally extrude PLA, and then push the new filament through. It's still hot enough to (partially) melt the ABS. There's no issue here. Also, you should use a spelling checker and perhaps not abbreviate "hotend".

I took care of the english as far as I could without changing the content in directions that might not reflect the authors intentions.

@TomvanderZanden you are right - issues with switching ABS>>PLA are not such common but I wanted to cover pesimistic scenario. So questioner would have bigger picture what can appear.

There's no problem with ABS->PLA, most ABS is printed at 200-250C (according to RepRap wiki, I use 240C) it's hotter then you would usually print with PLA but PLA does not burn at those temperatures, just yesterday I successfully printed an 8 hours job with PLA at 240C (on purpose, needed to test something), to switch from ABS to PLA just set your hotend to 230-240C and replace the filament normally, extrude until you see only PLA coming out of the nozzle then cool down to you preferred PLA printing temperture

@Nir it really depends on filament. I had one which were burning with smoke @ 240C. Nevertheless I've never had any problems cleaning extruder as I performed mentioned steps. And another 2 cents - when you do print then you can even exceed temperature as filament flows continuesly (vase). It gives curious effects ;) and sticks layers extraordinarily.

As Anton mentions, cleaning your nozzle is commonly done using a cold pull (or atomic pull). This process involves pulling out your filament from the nozzle while it is still semi-hot. (PLA, for instance will often be pulled at 80-90 celsius, which is the temperature at which it will slowly start to soften.)
The reason why this works is because the filament will stick better to itself when semi-hot, than to the nozzle, and pulling it out in this manner will most likely bring any residue along with it.
This question debates it further, while the video Anton posted demonstrates it well.

I've found a blow torch to work pretty well for clogged nozzles. Note: If your hotend use PTFE tubing internally DONT DO THIS or it may melt and ruin the nozzle.

Or you can use atomic nozle clianning!It woks fine for me :)
https://www.youtube.com/watch?v=04T8zdgyh3E

Hi, Anton. Here on SE we try to avoid link only answers as much as possible. Please consider making your answer readable without visiting the link. I made an example of this in a separate answer: feel free to use what I wrote, and I will delete my own answer.

Okay, I'll do that next time :) Nice chance to develop your skill to explain!

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authors: Ирина Акулинкина


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Increased issues with filament grinding
I have a FlashForge CreatorX (MakerBot clone) that's been working fine for about 15 months. Int he past month, I started noticing "thin" layers in some of my ABS prints. I finally tracked the issue down to the extruder gear grinding the filament (after a while, enough filament had ground off that the gear teeth were filled with plastic). I cleaned the gear twice before giving up on ABS and switching to PLA. Everything seemed ok until the PLA started doing the same thing during an overnight print (thin layers on prints, audible skipping during filament feed).
Raising the temperature on the extruder seems to fix the problem, but I'm now extruding PLA at 242 °C, much higher than I used to need. I worry that continued printing at this temperature will increase wear on the thermistor and increase my chances of clogging PLA in the gear (an issue I've had twice before).
Are there any common issues that cause this issue of filament not feeding properly? I've tried cleaning out the extruder head with wire and there don't seem to be any clogs…

Did you change filament vendor? Maybe this could be an issue.

If you can remove the feed pressure and feed filament by hand, what does the resistance feel like?  If it is high, you may need to clean the head.

After disassembling the extruder mechanism, I tracked the issue down to a clogged extruder… though not in the way I'd expected. A (previously?) common method to drop filament down to the hot end and create a heat-break between the heater and the extruder gear was the use of a PTFE (Teflon) sleeve. Over time, this sleeve can become clogged by filament that has melted and degraded/carbonized, sticking to the "nonstick" walls. This creates a bottleneck for the new filament, preventing smooth extrusion.

My printer came with two replacement tubes. Swapping those in for the old, clogged tubes resulted in instantly improved printing… sorta like getting a new printer! Print temperatures are back to normal and everything operates fine. I was also able to drill out the carbonized filament from the old sleeve, though I doubt I'll reuse it. I found replacement sleeves on Amazon here and an alternative, all-metal extruder assembly manufactured by Micro-Swiss. I'm not sure if you'd run into clogging issues on the all-metal one, so perhaps staying with the PTFE tubes and replacing them occasionally is a better way to go.

I've encountered this on my Replicator Dual in the past. I was only using MakerBot branded ABS filament, so it wasn't a quality issue for me.
What I found was that the delrin plunger design that "helps" keep the filament in contact with the drive gear wasn't actually helping. So, I installed the newer assemblies that use a spinning bearing to contact with the filament.

Install (or keep installed) a spring loaded extruder assembly.
When feeding filament, loosen the spring and gradually tighten until the filament begins feeding on its own.
Try to stay close to the recommended print temperatures for the material. ABS is typically somewhere around 225C, but it depends on the supplier.
Ensure your filament is stored in a dry place. This is way more of an issue for PLA, but it doesn't hurt to keep your material protected.
If it continues, perhaps swap out the drive gear itself. If you've dropped your motor or somehow a burr has developed on any of the teeth, naturally the burr will cut away the material. Gears are very temperamental and should be considered a consumable.

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How to remove a PLA print stuck to a BuildTak sheet
BuildTak is great because the printed plastic really sticks to it, it pretty much solved all the problems I had with prints detaching from the buildplate during printing.
However, it does sometimes cause the opposite problem of prints sticking too much and just not detaching from the build plate.
I'm specifically not asking how to prevent this from happening - I'm asking what to do after I made a mistake and now have a print that isn't coming loose.

I would do as fred_dot_u initially suggested, by increasing the bed temp (or using a hair dryer) to heat the BuildTak. Then, use a small fan to quickly cool the platform (or at least quicker than room temperature). An ice pack on the build plate/part could also work. This drastic fluctuation between the build platform (or BuildTak) and the part should make it easier to remove the part.
This works because the temperature coefficient is going to be different between the build plate, BuildTak, and the 3D printed part. So, each part rises and falls in temperature at different rates. When objects are heated and cooled, they expand and contract (respectively). Essentially, as each object expands and contracts at different rates, the objects begin to separate.
A good example is if you've ever placed a jar into the fridge/freezer to make it easier to open. Typically the jar is glass and the lid is either plastic or metal. You'll notice that the lid is significantly easier to open, as opposed to its original state, because the lid and the jar physically react differently to temperature changes.
Also, here is a good article explaining a few different ways to remove a stuck part. (for prosperity sake, here's a quick list):

Brute force. Just try to yank on it until it pries off.
Sharp objects. Try using a small blade to get under a corner of the part and wiggle the part a bit. Careful not to break the blade and send it flying.
Utilize temperature difference. I already explained this above.
Use solvents. I didn't know this, but apparently there are solvents in the market that are targeted for 3D printing maintenance. Essentially its just an alcohol-based liquid...
Use floss. Another cool idea that's related to using a sharp object, using dental floss. Basically, any small object that you can remotely wiggle under the part and give you more leverage to yank on it.
Invest in a flexible build platform. I've personally heard some mixed reviews on these (in present day of 2016). But material science is getting better every year, so who knows what will be available soon.

With using sharp objects, a wood chisel works well.

If you have a heated bed, bring the bed up to a reasonable temperature, then do as best as you can to create rapid cooling. If you can remove the bed, heated or not, consider to place it in a freezer or refrigerator. Obviously, if the bed is heated, you'll want to handle the bed carefully and not place it on anything in the freezer that could be damaged while it cools.
Unrealistically, pour liquid nitrogen over the bed. This may crack the bed and/or the model, as well as be all the more dangerous for unprotected users.

Use dental floss. It sounds a bit crazy, but I tried it for the first time yesterday, and it works like a charm.

Wrap the floss around two handles for comfort.
Loop the floss over the print. All the way down against the build plate.
Start pulling towards yourself, slowly but firmly.
Work the floss side to side if necessary.

Once the floss makes it all the way to the front side of the print, it will be removed from the buildtak cleanly, without torqueing the bed unnecessary, or popping the print of suddenly and flinging it across the room.

Glide style floss works better than waxed.

Interesting idea, but requires a lip. Most of the time when my prints are stuck there is no easy to access lip.

Give it a shot, the last model I printed didn't have any lip to speak of and the floss still worked.  Floss is intended to get between things, a little bit of back and forth should do the trick.


text:
What is the least expensive 3D printer?
What is the least expensive 3D printer available today? I am looking for something suitable for general use in a home office.

How is this opinion based? Good factual answers are possible.

I disagree that "factual" answers can be applied here. Least expensive questions just take us down the rabbit hole of "recycled printers" made from DVD drives that have a print volume of less than one cubic inch in the name of "$20" in an Arduino and the rest is recycled.

I read "available" as "able to be purchased as a complete [kit or assembled] unit", given the casual form of OP's question.

It's a shopping question. The stack as a whole bans them.

Monoprice has a Select Mini printer and sometimes lists it in "Open Box" condition for $99.

Search https://www.3dprintersonlinestore.com/product/personal, they have a lot of variety, from mini printer to larger format (bed area x height), one filament or two, and kits or assembled units.  I bought a Migbot i3 a few years ago (Prusa copy pretty much) for 179 USD, similar units from Geetech are now going for169. May take some fiddling to get it running (we had a mix of our own assembly errors, some extruder parts installed flipped 180 degrees, and some cable issues (motor cables; needed 1-2-3-4 at the 4-pin control board and 1---3-2---4 at the 6-pin motor end (2 not used pins).

Depends on your definition of "available" and your definition of "suitable for general use."
The cheapest 3D printers are mostly Kickstarter promises that take a year or more to ship, if they ever do. For example, the Peachy 3D printer Kickstarter just imploded and failed. There have been many other failed low-cost 3D printer crowdfunding campaigns. Another low cost Kickstarter printer, the 101Hero, is ongoing now (May 2016), but most competent observers I've talked to don't believe it will succeed at delivering working printers to all backers at that price point. If they do deliver, it will be painfully low-cost components and the printer will not perform well or last long. Stay away from crowdfunding campaigns for your first printer. At best, you get a beta product with lots of kinks to work out. At worst, you get nothing and lose your money.
For actual products you can purchase today, there's a wide spectrum of quality/cost tradeoffs.

Under \$200 there's nothing credible. The Tiko (\$179) might deliver, but post-Kickstarter units are widely expected to cost more.
Around \$200-300 you get into low-quality Prusa i3 kits from China. These aren't a great value -- most people end up spending another few hundred dollars on upgrades to get them working reliably and with high quality.
Around \$300-400 you can get an ok 3D printer, often with "chipped" proprietary filament so the vendor can make high profits on locked-in consumables. ("Razors and blades" model.) For example, the XYZPrinting Da Vinci Jr is \$350 but locks you into high-cost chipped filament. The Wanhao Duplicator i3 is currently a community favorite for value-for-money at \$399. The Printrbot Play is much higher quality/reliability but much smaller at the same price.
If you get up around \$600, a big range of decent printers opens up. But this is no longer the "least expensive" option, so I won't get into it.

If you want to tinker, the Duplicator i3 is a good choice. If you want a machine that just prints, the Play is a good choice. There are other printers and cheaper printers, but most of what you'll find below $400 is going to end up causing pain unless your goal is simply to tinker with printer troubleshooting and upgrades.

I can vouch for the duplicator i3 as a good option. I've bought one and the value for money is quite good

Just as a counterpoint, my first (so far only) 3D printer was the New Matter mod-T. I joined their Indegogo campaign and, while the delivery was delayed a couple of times, I did eventually receive my printer and it works as advertised. Just wanted to point out that, despite some high-profile failures, not all crowdfunded 3D printers are doomed.

I got the 101Hero, it works reasonably well as expected at this price point. The motors are fragile, getting it calibrated well is a pain, there is no included fan so you have issues when printing spires, and the print resolution is bad.

I ordered the Tiko years ago from KickStarter but they have problems with producing them as they ran out of funds. The first 5,000 Tiko's have been delivered but the rest is delayed indefinitely. They are looking for someone willing to invest in this 3D printer so they can ship all the other printers as promised.

You can get an A8 3D printer on Gearbest at 149$, It's a version of an i3, with easy assemble and pre configured, and it have a suprising good quality.
I thinks is the best price/quality that you can find at the moment. It prints with a good quality by default and you can upgrade it if you need it without spending hundreds of dollars.
http://www.gearbest.com/3d-printers-3d-printer-kits/pp_337314.html


text:
Slic3r under extrusion
For last two weeks I have been struggling with flow rate adjustments. I'm using an UM2, colorFabb XT 1.75mm and Slic3r. Before printing a test cube I made flow rate adjustments using the "Perimeter test" (printed a hallow cube with 1 layer thin perimeter line). I then compared the desired value of the perimeter's width with the value from the g-code and adjusted the flow rate. I repeated this procedure until I got exactly the thickness I needed. After that, I printed a 15x15x15 mm cube and observed under extrusion on top layer. Also, the dimensions of the cube in the x-y plane were smaller than expected (0.4mm shorter than they should be). I have done this a few times now, and still get the same result. :/ Furthermore, I was unable to adjust width by dividing the desired value of the width of the perimeter by a real value, I got slightly smaller extrusion multiplier (One I got by division is 0.9 , but 9.5 relates to desired width). Do you have some suggestion guys?
Update:
I'll try to explain the calibration method I have used.

I have made in Solidwork 15x15x15 mm cube.
The cube was imported into Slic3r, where I have set the infill to 0% and number of sides shells equal to 1 and number of top and bottom shells equal to 0 (It gave me one layer thin wall in shape of cube).
I printed it out and measured the width using caliper and compared with the perimeter's width from g-code.
I have got something about 0.7, but the extrusion width in g-code is 0.65, so I changed extrusion multiplier by 0.65/0.7 = 0.93 (what is not actually true, because I got correct value on 0.95 only)
I have repeated the procedure for many times, and always got wrong dimensions and under extrusion.
There is the video about method I just have explained: https://www.youtube.com/watch?v=cnjE5udkNEA

Could you please crop your image a bit?

Hi! Do you have a link or reference to the tuning method you are using? I'm not sure how perimeter tests work. :)

@Anton when you add image and imgur already grabed it then you can add 's' letter to image link so it will become small or 'm' for middle. Letter should go as last just before dot

I'll try to explain method I have used.

@AntonOsadchy I tried to explain why you get underextrusion (or pseudo-underextrusion) on top layers. I haven't cover underextrusion in terms of perimeter dimension. Another remark - your point #2 is almost equal to "vase" option :)

@darth pixel yes, I guess you are right about top layers! I'll try to make an experiment tomorrow and see what I'll get. But it still doesn't really explain the problem with x-y dimensions, which should be solved by adjusting the filament flow. I have actually seen some articles, where people could get very good precision (about 0.05 mm) by adjusting the filament flow using this method. But it doesn't work for me :/ Anyway, I highly appreciate your help :)

@darthpixel I have a vase mode turned off. What do you mean by equal to "vase" option?

@AntonOsadchy vase mode has 1 perimeter and no top layer, that's why I've wrote "almost equal to vase" ;)

It looks like you overtune it. I think it's because top layer of hollow object doesn't have any support (which is obvious) but because of that the filament is not oblate that's why it looks like underextruded.
If you really need hollow object then set number of top layers to 3..5 then check if it helps. I know it's not really what you expect but IMO this could help here. (I usually set 2 bottom layers and 3 top and it's quite enought.) You can also experiment with speed of top leyer. I would say the faster the better in this issue as the the first top layer should be as flat as possible then next top layer will have better support. And of course cooling should be set to max (as for the bridges).
Here is an explanation why you get underextrusion.

A is wall (perimeter) B is (ceiling) top layer.
Empty outlines are what you expect but filled shapes are what you really get. Differences are of course slightly smaller but it's to clearly explain the issue
Please also check Printer Settings > Advanced > Top solid infill.

I just have found interesting article about flow math of slic3r (http://manual.slic3r.org/advanced/flow-math) , where they suggest to use maximal value of extrusion width equal to 1.7*nozzle size. In my case I use 0.65, what is quite close to maximal extrusion width for nozzle with diameter of 0.4mm (0.67mm max) . I'll try to change it and see how it will affect the result.

I've had that issue on my 3D printing shop.
That kind of problem usually happens when the extruder driving gear gets worn out. This makes the extruder loose it's grip on the filament and diminishes the flow of the extrusion, resulting on the prints you show on your photo.
Depending on the time you have with your printer and the use you give it the gear will get worn out between 8 to 12 months and you will have to change it to avoid the flow issues.
I recommend you to open the extruder and check if the driving gear is worn so that you can order a new one.


text:
How to display images on DLP using HDMI for 3D printing?
I am working on a DLP based 3D printer. I already sliced my STL file to multiple layers. Each layer is saved as a SVG file. Because its an SVG file, I can always convert each layer to PNG/JPG file if desired.
I have a TI DLP Lightcrafter 4500 module connected to my laptop using the HDMI. The DLP shows up as a second monitor on my laptop. I am using LabVIEW to control all components of the printer.
Question 1: How I can programmatically display my desired image file on the DLP projector. I would prefer to use Python or LabVIEW to display my desired image onto the entire screen of the DLP. Is there any way to achieve this on Windows? I also have the option of using Raspberry Pi + LabVIEW using LINX (http://www.labviewmakerhub.com/). I looked at nanoDLP (http://www.nanodlp.com/), which is a control software for DLP based 3D printers. However, I can't figure out how they manage to display the desired images to the DLP.
Question 2: Is it possible to display a SVG file to the DLP instead of PNG/JPG/BMP? If not, how do I know which resolution to use when converting SVG to PNG/JPG/BMP?

I suppose it's not a solution but maybe it will help you anyway. You could use this app http://www.stefandidak.com/windows-layout-manager/ it allows you to say - this window will be open here. Experiment with names/processes and other "selectors". I use it with success.

I believe most people building DLP printers simply use Creation Workshop. It's free (older versions) and pretty powerful for this.

Q1: Printrun is 3D printer host software written in Python with limited DLP support. You can checkout how it display layers.
NanoDLP directly talk to GPU through Dispmanx which makes it Raspberry Pi only.
Q2: Printrun supports SVG. To convert SVG (multi-layer) to PNG you can use ImageMagick cli tools, you should consider your projector resolution too.


text:
3D Printer Stringing after nth layer
Quick Question.
My Printer is the CTC clone of the Makerbot Replicator Dual.
For my past few prints after nth layer the print just starts to go stringy. Here is an example:

I am currently using MakerWare with the following settings
{
   "_attached_extruders" : [ "mk8", "mk8" ],
   "_bot" : "replicatordual",
   "_extruders" : [ 0 ],
   "_materials" : [ "pla", "pla" ],
   "adjacentFillLeakyConnections" : false,
   "adjacentFillLeakyDistanceRatio" : 0,
   "anchorExtrusionAmount" : 5.0,
   "anchorExtrusionSpeed" : 2.0,
   "anchorWidth" : 2.0,
   "backlashEpsilon" : 0.050,
   "backlashFeedback" : 0.90,
   "backlashX" : 0.0,
   "backlashY" : 0.090,
   "bedZOffset" : 0.0,
   "bridgeAnchorMinimumLength" : 0.80,
   "bridgeAnchorWidth" : 0.80,
   "bridgeMaximumLength" : 80.0,
   "bridgeSpacingMultiplier" : 1.0,
   "coarseness" : 9.999999747378752e-005,
   "commentClose" : "",
   "commentOpen" : ";",
   "computeVolumeLike2_1_0" : false,
   "defaultExtruder" : 0,
   "defaultRaftMaterial" : 0,
   "defaultSupportMaterial" : 0,
   "description" : "",
   "doAnchor" : true,
   "doBacklashCompensation" : false,
   "doBreakawaySupport" : false,
   "doBridging" : true,
   "doDynamicSpeed" : false,
   "doDynamicSpeedGradually" : true,
   "doDynamicSpeedInteriorShells" : false,
   "doDynamicSpeedOutermostShell" : true,
   "doExponentialDeceleration" : false,
   "doExternalSpurs" : true,
   "doFixedLayerStart" : false,
   "doFixedShellStart" : true,
   "doInfills" : true,
   "doInsets" : true,
   "doInternalSpurs" : false,
   "doMixedRaft" : true,
   "doMixedSupport" : true,
   "doOutlines" : true,
   "doPrintLayerMessages" : false,
   "doPrintProgress" : true,
   "doPurgeWall" : false,
   "doRaft" : false,
   "doSplitLongMoves" : true,
   "doSupport" : false,
   "doSupportUnderBridges" : false,
   "endGcode" : "",
   "exponentialDecelerationMinSpeed" : 0.0,
   "extruderProfiles" : [
      {
         "bridgesExtrusionProfile" : "bridges",
         "feedDiameter" : 1.769999980926514,
         "feedstockMultiplier" : 0.9300000000000001,
         "firstLayerExtrusionProfile" : "firstLayer",
         "firstLayerRaftExtrusionProfile" : "firstLayerRaft",
         "floorSurfaceFillsExtrusionProfile" : "floorSurfaceFills",
         "infillsExtrusionProfile" : "infill",
         "insetsExtrusionProfile" : "insets",
         "layerHeight" : 0.20,
         "maxSparseFillThickness" : 0.10,
         "nozzleDiameter" : 0.40,
         "outlinesExtrusionProfile" : "outlines",
         "raftBaseExtrusionProfile" : "raftBase",
         "raftExtrusionProfile" : "raft",
         "restartExtraDistance" : 0.0,
         "restartExtraDistance2" : 0,
         "restartExtraRate" : 25.0,
         "restartExtraRate2" : -1,
         "restartRate" : 25.0,
         "restartRate2" : 25,
         "retractDistance" : 1.299999952316284,
         "retractDistance2" : 0,
         "retractRate" : 25.0,
         "retractRate2" : 50,
         "roofSurfaceFillsExtrusionProfile" : "roofSurfaceFills",
         "sparseRoofSurfaceFillsExtrusionProfile" : "sparseRoofSurfaceFills",
         "toolchangeRestartDistance" : 18.50,
         "toolchangeRestartRate" : 6.0,
         "toolchangeRetractDistance" : 19.0,
         "toolchangeRetractRate" : 6.0
      },
      {
         "bridgesExtrusionProfile" : "bridges",
         "feedDiameter" : 1.769999980926514,
         "feedstockMultiplier" : 0.9300000000000001,
         "firstLayerExtrusionProfile" : "firstLayer",
         "firstLayerRaftExtrusionProfile" : "firstLayerRaft",
         "floorSurfaceFillsExtrusionProfile" : "floorSurfaceFills",
         "infillsExtrusionProfile" : "infill",
         "insetsExtrusionProfile" : "insets",
         "layerHeight" : 0.20,
         "maxSparseFillThickness" : 0.10,
         "nozzleDiameter" : 0.40,
         "outlinesExtrusionProfile" : "outlines",
         "raftBaseExtrusionProfile" : "raftBase",
         "raftExtrusionProfile" : "raft",
         "restartExtraDistance" : 0.0,
         "restartExtraDistance2" : 0,
         "restartExtraRate" : 25.0,
         "restartExtraRate2" : -1,
         "restartRate" : 25.0,
         "restartRate2" : 25,
         "retractDistance" : 1.299999952316284,
         "retractDistance2" : 0,
         "retractRate" : 25.0,
         "retractRate2" : 50,
         "roofSurfaceFillsExtrusionProfile" : "roofSurfaceFills",
         "sparseRoofSurfaceFillsExtrusionProfile" : "sparseRoofSurfaceFills",
         "toolchangeRestartDistance" : 18.50,
         "toolchangeRestartRate" : 6.0,
         "toolchangeRetractDistance" : 19.0,
         "toolchangeRetractRate" : 6.0
      }
   ],
   "extruderTemp0" : 208,
   "extruderTemp1" : 200,
   "extrusionProfiles" : {
      "bridges" : {
         "fanSpeed" : 0.50,
         "feedrate" : 40.0
      },
      "firstLayer" : {
         "fanSpeed" : 0.50,
         "feedrate" : 5.0
      },
      "firstLayerRaft" : {
         "fanSpeed" : 0.50,
         "feedrate" : 50.0
      },
      "floorSurfaceFills" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      },
      "infill" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      },
      "insets" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      },
      "outlines" : {
         "fanSpeed" : 0.50,
         "feedrate" : 40.0
      },
      "raft" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      },
      "raftBase" : {
         "fanSpeed" : 0.50,
         "feedrate" : 10.0
      },
      "roofSurfaceFills" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      },
      "sparseRoofSurfaceFills" : {
         "fanSpeed" : 0.50,
         "feedrate" : 90.0
      }
   },
   "fixedLayerStartX" : 0.0,
   "fixedLayerStartY" : 0.0,
   "fixedShellStartDirection" : 215.0,
   "floorSolidThickness" : 0,
   "floorSurfaceThickness" : 0,
   "floorThickness" : 2.0,
   "gridSpacingMultiplier" : 0.990,
   "infillDensity" : 0.05000000074505806,
   "infillOrientationInterval" : 90,
   "infillOrientationOffset" : 0,
   "infillOrientationRange" : 90,
   "infillShellSpacingMultiplier" : 0.70,
   "insetDistanceMultiplier" : 1.0,
   "jsonToolpathOutput" : false,
   "layerHeight" : 0.250,
   "leakyConnectionsAdjacentDistance" : 0.0,
   "maxConnectionLength" : 10.0,
   "maxSparseFillThickness" : 0.250,
   "maxSpurWidth" : 0.50,
   "minLayerDuration" : 5.0,
   "minLayerHeight" : 0.010,
   "minRaftBaseGap" : 0.0,
   "minSpeedMultiplier" : 0.30,
   "minSpurLength" : 0.340,
   "minSpurWidth" : 0.120,
   "minThickInfillImprovement" : 1.0,
   "modelFillProfiles" : {},
   "numberOfShells" : 3,
   "platformTemp" : 70,
   "purgeBucketSide" : 4.0,
   "purgeWallBaseFilamentWidth" : 2.0,
   "purgeWallBasePatternLength" : 10.0,
   "purgeWallBasePatternWidth" : 8.0,
   "purgeWallModelOffset" : 2.0,
   "purgeWallPatternWidth" : 2.0,
   "purgeWallSpacing" : 1.0,
   "purgeWallWidth" : 0.50,
   "purgeWallXLength" : 30.0,
   "raftAligned" : true,
   "raftBaseAngle" : 0.0,
   "raftBaseDensity" : 0.6999999880790710,
   "raftBaseLayers" : 1,
   "raftBaseRunGapRatio" : 0.8000000119209290,
   "raftBaseRunLength" : 15.0,
   "raftBaseThickness" : 0.3000000119209290,
   "raftBaseWidth" : 2.50,
   "raftExtraOffset" : 0.0,
   "raftFillProfiles" : {},
   "raftInterfaceAngle" : 45.0,
   "raftInterfaceDensity" : 0.3000000119209290,
   "raftInterfaceLayers" : 2,
   "raftInterfaceThickness" : 0.2700000107288361,
   "raftInterfaceWidth" : 0.4000000059604645,
   "raftModelSpacing" : 0.2199999988079071,
   "raftOutset" : 4.0,
   "raftSurfaceAngle" : 0.0,
   "raftSurfaceLayers" : 3,
   "raftSurfaceShellSpacingMultiplier" : 0.70,
   "raftSurfaceShells" : 2,
   "raftSurfaceThickness" : 0.2700000107288361,
   "roofAnchorMargin" : 0.40,
   "roofSolidThickness" : 0,
   "roofSurfaceThickness" : 0,
   "roofThickness" : 2.0,
   "shellsLeakyConnections" : false,
   "solidFillOrientationInterval" : 90,
   "solidFillOrientationOffset" : -45,
   "solidFillOrientationRange" : 90,
   "sparseInfillPattern" : "hexagonal",
   "splitMinimumDistance" : 0.40,
   "spurOverlap" : 0.0010,
   "startGcode" : "",
   "startPosition" : {
      "x" : -112,
      "y" : -73,
      "z" : 0
   },
   "supportAligned" : true,
   "supportAngle" : 68.0,
   "supportDensity" : 0.2000000029802322,
   "supportExcessive" : false,
   "supportExtraDistance" : 0.50,
   "supportFillProfiles" : {},
   "supportLayerHeight" : 0.250,
   "supportLeakyConnections" : true,
   "supportModelSpacing" : 0.4000000059604645,
   "supportRoofModelSpacing" : 0.4000000059604645,
   "thickLayerThreshold" : 0,
   "thickLayerVolumeMultiplier" : 1,
   "travelSpeedXY" : 150.0,
   "travelSpeedZ" : 23.0,
   "version" : "3.9.3"
}

If anybody has any ideas please let me know.
Thank You

Does the issue appear after the printer has "changed action", such as started to print an area that require very frequent retraction? Also, does this happen only for one or several different models?

I don't know what was the object like in your plans but it looks like your extruder stopped pushing filament well. I had similar effect when I used extensive retraction with low quality filament. In fact filament was to soft and when it was pressed to hobbed pulley/bolt it became flatened and then stopped flowing. So if your case is similar you could check the following:

spring tenssion
knurls
filament diameter

It's also worth to check if hobbed pulley is screwed tight on motor shaft.
[edit]
It could be also caused by too fast retraction if knurls are not sharp enough they can slide on or scrap filament.
When you notice that again, stop printing proces, lose springs and pull out filament from hotend and inspect its shape.

@TormodHaugene that was my first thought too...

If it was made in the last couple years, it has a PTFE-lined hot end. Checking the condition of the PTFE liner would be a very good troubleshooting step. If it's charred/degraded, it can cause this. Checking the extruder spring arm tension is another good one.


text:
Repetier Host stops sending commands to printer when switching Windows user
I'm running Repetier Host v1.6.1 with Repetier Firmware v0.92.9.  My computer is running Windows 7 Pro SP1, 64-bit.
If I set a print going via USB then switch to another user (note: I do not log out), then the pinter's display shows that the command buffer drops from 16 to 0 until it stops printing altogether.  If I switch back to the user that is running Repetier Host then the buffer fills up again and the print job resumes.
Before I updated Repetier Host this didn't happen, I could leave it running while I switched users and the job would run just fine.  I'm not sure why this behaviour has changed, but is there any way to get it to run properly under a background user?

Now, obviously there are workarounds, like putting the job on an SD card or just not switching users.  Those are not solutions, they are workarounds, so please don't suggest them.

Maybe your windows settings were changed. What about switching user with/witout logging off? http://windows.microsoft.com/en-us/windows/switch-users-without-logging-off#1TC=windows-7

Yes, I am switching users without logging off.  If I log off, Repetier Host will close and then the print job would be irretrievably lost.

Is it possible that in updating Repetier you inadvertently installed it for a single user rather than for everyone? If so, that might account for its stopping when the user is changed.

I believe what happens here is that Windows suspends the process running the print job, either due to the program not being in focus, because you switch user, or both.
You could try to increase the priority of the print process in task manager, and see if that helps.
In Windows 7:

Open Task Manager
In the Applications tab, right click the application, and select Go To Process, which will take you to its background process in the Process tab.
Right click the process, go to Set Priority and select some priority higher than the current level.

In Windows 10:

Open Task Manager
In the Processes tab, right click the application, and select Go To Details, which will take you to its background process in the Details tab.
Right click the process, go to Set Priority and select some priority higher than the current level.

PS: Avoid setting the priority to Realtime, as that effectively will give the process full control of your computer's resources, which could kneel your computer if the program is poorly written.

I doubt this is a priority issue. It's rather set application in suspend/slip mode. Switching user (with logout) doesn't consider priority AFAIK.

Just tried it and changing the process priority has no effect.  I didn't try realtime, but it doesn't look like it would matter.  The issue occurs the moment I drop out to the user selection screen, and there are no other programs taking up system resources when I do that.

If it stops the moment you change user, then priority probably doesn't matter at all. Turning off suspend-mode for the print process might work, as @darthpixel mentions. However, when you say that you change user, do you actually log out the first user, or are you only switching user? I am asking because there seems to be a difference.

No, I do not log out,  I switch user.  What do you mean by turning off suspend-mode though?

That is a good question. I found this post, which could be worth trying. It seems like a developer feature where /enableDebug turns off the standard lifecycle handling for the app in Windows, while /disableDebug enables it again. I understand that such a solution might not be for everyone, though! :)

Okay, thanks, but that seems to refer to programming apps for the Windows Store.  I'm not on that platform and I'm not programming Repetier Host, so I don't think I can make use of that.

Yeah, you might be right. Thought it was worth mentioning, though!

Maybe you've changed your power settings and that's why your USB port stops working when switching user (for power conservation). I know you've said it was working before Reptier update but maybe it's worth to check.

So go to Start > Control Panel > Power Options

Find your (selected) power plan and choose Change plan settings > Change advanced power settings
Then check USB Settings > USB selective suspend settings
to be sure - set both to Disable

Another place to check is My Computer > Manage > Device Manager > Universal Serial Bus controllers

And here there are at least 2 items to check

Generic USB Hub
USB Root Hub

both have tab Power Management and checkbox Allow computer to turn off this device to save power - uncheck them
I know it doesn't sound very wise but who knows... :)

Alas, changing the USB Selective Suspend settings made no difference, in fact they were already enabled, but I tried disabling just to be sure.  Also, the USB hubs already had the "allow to turn off" setting disabled.  I did learn something about the USB hubs though, the fact that they actually name what's attached to them and the devices' power draw is a useful feature that I'd never explored.


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Bonding PETG to glass
I'm thinking of trying my hand at fabricating microfluidic devices. I'll be using a filament based on PETG (Zortrax's Z-glass filament, which is translucent and resistant to acids and bases). For my plan to work, I'll need to find a good way to bond the PETG model onto a glass microscope slide.
What is the best technique for doing this? Should I use epoxy resin or some other adhesive, or can I solvent bond it? I've heard stories about PETG permanently bonding to a glass print bed, so it seems plausible that solvent bonding might work. Will it work, and if so, what solvent should I use?

Nathaniel, were you able to solve this problem?
We have similar issues here. Trying to bond PET-G to a glass microscopy slide...

@SébastjenSchoenaers sorry, we ended up changing plans and not building this device. If you have any success it would be interesting to hear about your results, though!

@SébastjenSchoenaers I just remembered why we changed plans: it turns out that you can make microfluidic devices very easily by cutting shapes out of Parafilm and sandwiching it between two slides. A craft knife works ok, but the Silhouette Portrait paper cutting machine works even better and is inexpensive. It won't work for every purpose of course, but it's what we ended up using instead.

Any chance you can set up the glass you want to bond to as your build plate.  Maybe heat the glass to 100C to build on.  People have reported getting PETG to bond to glass build plates so strong that it pulls out chunks of the glass build plate.

@PerryWebb at the time of asking the question I was using the Zortrax M200, which would have made that impossible, because it was a very closed-source machine and there was no option to print without a raft! If I was trying to do the same thing now, I'd probably try that.

The solvents that can dissolve PET are pretty nasty -- I wouldn't personally handle any of them outside a lab fume hood. If you have that, a 50/50 mix of MEK and methylene chloride should work. (Increase MEK ratio if you want faster adhesion / less working time, and vice versa.)
First thing I would try is printing directly onto the (super clean) glass. Print the first layer at high temp to try to get a good bond. Then over-extrude to get watertight perimeters. It MIGHT be better to print on a cold bed to keep the PET from popping off when the glass cools, but you would need to do some experimenting.
You could also try heating the slide to the melting temp of PET on a hot plate and then attaching the printed part.
Failing that, a transparent superglue could be a good approach.

Thanks, this is very useful advice. Just heating the glass and melting it on seems like an easy first thing to try. The others sound a bit trickier, though we do have fume hoods. (I don't think I can try printing straight onto the glass unfortunately, because the Zortrax is a pretty closed system and doesn't give me control over those parameters.) I'll let you know if and when I try any of these!

Oh yeah, mandatory rafts will keep you from printing onto the glass. I hadn't thought of that.

Mandatory rafts and also mandatory autocalibration. If I put a glass slide on top of the build platform I'm pretty sure it will just smash the glass, because the first thing it always does is raise the platform until the nozzle makes electrical contact with it. It's an excellent machine, just not really suited to experimenting with technique.


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Grease for PLA sprocket
I am attempting to construct model tank tracks with accompanying wheels and sprockets. All parts will be printed in PLA. The tracks will be driven by electric motors.
What would be a suitable grease for this project to minimize friction without damaging the plastics.

I've also found this link on reprap wiki http://reprap.org/wiki/Lubrication it covers all aspects of lubricating stuff (not only plastics)

I'm gonna be the simpleton here and say grease is grease. The difference between grease and no grease is 20-fold and more. The difference between your ideal grease and peanutbutter is 2-fold at most. Print sprockets in Nylon. If they are small they will not warp and you just extended lifetime 10 fold.

Grease on plastic parts can weaken the plastic, particularly if it's petroleum based. I have found that paraffin wax from a candle or crayon works very well as a dry lubricant for PLA. If you must use grease, use a PTFE or silicone-based grease.

@Anachronist, Paraffin wax is obtained from petroleum by dewaxing light lubricating oil stocks.

@DwightSpencer - yes, it depends on the compound, of which many are derived from petroleum. However, after investigating, this chart - https://www.plasticsintl.com/chemical-resistance-chart - shows that both vaseline and paraffin are safe for most plastics although PLA isn't included in that chart. I prefer paraffin because it's dry.

@Anachronist right and a good chart. But they most likely left PLA out of there because of its low to non-existent chemical resistance to anything but water, as pointed out in https://prusament.com/chemical-resistance-of-3d-printing-materials/ and is particually week to Hydrocarbons such as the CnH2n+2 in Paraffin and C2H6O in Ethanol or C3H60 in Acetone of which are close enough to PLA's chemical make up of (C3H4O2)n.

@DwightSpencer - thank you. I haven't noticed paraffin degrade PLA; in fact it improves the performance of bearings and gears, so I routinely lubricate moving PLA parts by rubbing a crayon or candle on them. It's also dry and not messy. If wax is damaging to PLA, then what would be a good lubricant?

@Anachronist Love Integza for his video on this sort of thing. He found that powder graphite is a good lubricant. Also, unless your printer is only able to do PLA; change materials. PET, ABS or anything else that has a better chemical resistance to the lubricant of choice would work. Most experiments show that Polyamide and polycarbonate being durable materials for workloads like sprockets. I mean it's just material science. Print a part. Do a experiment to see its break/wear points. Then adjust your engineered design to fit the use case. There isn't a single solution here just trade-offs.

@DwightSpencer thanks again. The only Integza I found on YouTube has a lot of videos about rocket propellant and combustion engines. The same guy? My printer can print anything including nylon (which is best for gears), but PLA is the most trouble-free material to print.

@Anachronist yeah that's the guy. He's big in the 3d printing and maker community. His latest series has been around rockets but check his earlier works.

I use cosmetic vaseline - petroleum jelly. Usually it is white to transparent and odorless. It's cheap and available in all drugstores and cosmetics stores.
As suggested by Tom van der Zanden I'm adding additional info about interactions of vaseline and plastics.
I've found many web sites which claim that vaseline can damage plastics but none of them really proved that statement. There is nothing about it neither on producers sites nor wikipedia or any other believable sources I've found. So according to it and my practice I'm pretty sure that vaseline won't damage popular plastics (including common filaments).
The only information I've found is that vaseline can damage natural rubber but I cannot confirm that on my own.
Of course it might not be true for some materials so be careful and check the interactions first on invisible side or on refuses.

This answer could benefit from some additional motivation, especially concerning the possibility of vaseline damaging plastics and whether it minimizes friction (compared to other lubricants).

@TomvanderZanden you are right, I'll add such information soon.

Paraffin wax works well for me as a dry lubricant for PLA parts.

You may find a solution with the common lubricant containing PTFE, often called Super Lube. It is described in manufacturer's literature as non-reactive with virtually everything. It is available at a reasonable price as plumber's grease (look for either Teflon or PTFE in the ingredients) in various quantity containers. When used on metal, you may get black residue. With plastic, some color of the plastic will appear as the surfaces wear. It has good sticking power too.

I have been using sewing machine oil for my 3D printed extruder gear for a couple of years, without any noticeable wear so far.
In general, I believe any kind of low viscosity oil would do, but then again, it also depends on the environment in which you plan to use the model. If you plan on using it outside, for instance, you probably should get some grease that does not attract dirt, as the dirt itself will grind down the gears quickly.

darth pixel's link for lube information indicates that light oil provides relatively poor lubrication, but reduces noise and collects dust. Interesting to read that WD-40 is listed as the worst. Cyclists have discovered that it's worse than no lube at all for a bike chain and it's not a surprise to learn that it's not good for 3d printers either.

@fred_dot_u I totally agree that WD-40 is the worst grease and it's sometimes worse than no lube at all. IMO it's too light to use it as grease. Especially for long term greasing. I use WD-40 all the time but NOT as greas but to clean links and to relax and unscrew a screw only. IMO there is too less grease (lubricant) in WD-40 for application as bike chain or even door hinge. fred_dot_u please notice that there is special WD-40 bike which confirms that WD-40 (regular) is not very good for bikes.

@fred_dot_u, I am not familiar with the WD-40 series, but I understand and agree your concern. The OP does not specify the environment in which the tank treads will be used, but if it is to be used outside, protection from grit and dirt probably should be considered. That being said, my 3D printer stays much cleaner than my bicycle chain. :-)

@TormodHaugene there is really strange issue with WD-40. I don't know how is it possible that this stuff is a synonym of grease in some groups of people. WD stands for water displacement and it was "developed" to remove greasing (sic!) and rust as far as i know. I don't know any mechanics specialist who would use WD-40 as grease.

WD-40 is the single most overrated substance in the public's mind. It's the only "lubricant" most people have in their homes. Completely undeserved reputation. (It's good for unsticking siezed things, so I think people assume it's also good for keeping them unstuck... but it's really terrible for long-term lubrication.)


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Failing slow extrusion after upgrade to E3D hotend
I recently upgraded to a E3D full hotend and I started to have problems with slowly printed parts. After I print first object and start next one, then the first layer has serious issue.

The first two test were extruded around 10mm/s, the right one around 15mm/s. The material is PLA (fillamentum.com) at temperature 210°C and nozzle diameter is 0.4mm. The Rebel II RepRap printer uses RAMPS with marlin firmware. I use Slic3r and Pronterface SW.
I didn't find answer in following troubleshooting guides:

Simplify3D - Print Quality Troubleshooting Guide
A visual Ultimaker troubleshooting guide
RepRap - Print Troubleshooting Pictorial Guide
all3dp.com - 16 Common 3D Printing Problems (And Solutions)

Do you have an idea what can cause this issue?
Update
I did a new print, where I just heat the hotend and start printing immediately. This is the result:

Is it filled from below (which would mean it suddenly stop extruding well) or is it filled from above (which would mean it suddenly start extruding well)?

Under extrusion, ususally caused by going too fast vs your temp, or you have a clog / loose filament drive

What kind of e3d hotend is used?

It's e3d v5 hotend.

I bet your old and new extruders have different hobbed pulley/bolt effective diameter.
It looks like your new extruder has smaller hobbed diameter that's why it pushes too less material.
In MatterControl application there is a slider which allows user to tuneup extrude ratio on the fly (while printing). You coud check it so it would confirm the issue.
In Slic3r you could go to
Printer Settings > Advanced > Extrusion width
and experiment with it (especially with Default extrusion width)
Both (Slic3r and MC) could answer your question if it's extrusion ratio issue. If you confirm that - you can proceed with calibration. Here is method to calibrate extruder flow and general calibration article here.

I forgot to mention that I did calibration with the new hotend, where I also have changed the motor to lighter 1.8° version instead of original 0.9°. To be sure I didn't forget anything I will recheck the calibration.

Before considering any calibration you should compute the exact ideal steps per mm from the mechanical properties.

After I print first object and start next one, then the first layer has serious issue.

Are you leaving the hotend on between prints? If you leave an E3D hotend heated up while it's not printing, heat will slowly migrate up the heatbreak and start softening the filament there, which will subsequently become stuck. You should turn off the heat immediately after finishing your print (or, ideally, just have your end G-code contain a command to turn the hotend off).

Yes I am leaving hotend on. But the first object is pretty small, so I would expect to print first layer without problem. I will test this behavior.


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Should I consider health impact of ABS or PLA when printing cookie cutter?
Should I consider health impact of ABS or PLA when printing cookie cutter similar to image below?
How safe it is to use ABS or PLA for kitchenware in general?

If it's one-time-use, both ABS and PLA are perfectly safe for use as a cookie cutter.
The "food safety" of 3D printed parts is fairly controversial. In fact, whether any particular material is approved by regulators (such as the US FDA) for food contact is much more complex than most people realize. Materials can be accepted for some uses and not others. But there are two major considerations:

Does the material leach into the food, or does the food leach into the material?
Can the material be adequately cleaned and sterilized between repeated food exposures?

Whether leaching is a concern will depend on the kind of contact. For example, nylon will absorb acids but is often used for potable water service. ABS is fine for cold foods but not hot foods. PLA (injection grade) is often used for disposable plastic forks and cold beverage cups, but rarely reusable containers.
There is some anecdotal evidence that lots of 3D printing filaments, particularly cheap Asian filaments, contain toxic chemicals in the pigments and additives. Heavy metals like lead, cadmium, strontium, and all sorts of nasty organic chemicals have been found. You probably WON'T get any meaningful leaching of these chemicals in the brief exposure with cookie dough, but to be safe I would only use reputable US and EU filament manufacturers for food contact. I would also stick to filament colors that use non-toxic pigments (eg plain white is almost always safe titanium dioxide) or no pigments at all ("natural" color).
When it comes to cleaning a cookie cutter for multiple uses, ABS is probably a much better choice than PLA, because ABS can withstand fairly hot water without losing shape. PLA probably won't survive a cycle through the dishwasher. PETG is perhaps a better choice than ABS for longer contact with wet foods, but may or may not survive the dishwasher.
However, the porous structure of 3D printed parts is a serious problem for cleanliness. The tiny grain structure and voids between extruded strands can act as a safe haven for bacteria between uses. This is particularly an issue with cookie dough containing raw egg. A porous surface for raw-food handling would not be acceptable in a commercial kitchen.
Now, the odds of actually transmitting salmonella via poorly-cleaned cookie cutter may be fairly low. Lots of people cut meat at home on wooden cutting boards (which are also porous) and never get sick. Properly cooking the food immediately after handling will go a long way towards reducing the odds of harmful cross-contamination. You'll have to decide for yourself whether the risk profile is worth it. One-time use is the conservative choice.

Presumably another way to reduce the risks would be to use pasteurised powdered egg instead of raw egg.


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Raft hard to remove?
I've been having a hard time lately getting the raft off of my ABS prints.
Is that a symptom of either a nozzle or bed that are too hot? Or is there some other factor I should be looking in to?
I have an UP mini that I've modified both the nozzle and bed to customize the temperatures on.
Bed gets heated to 100˚C and nozzle is either 266˚C for UP ABS filament or 236˚C for off-brand ABS filament.

Hotter ABS is less viscous, so it can get into smaller microscopic cracks and holes in your bed and therefore be harder to remove later, as well as join the layers together more. This might be it. This is also the theory why ABS slurry (abs+acetone mixture) works so well for bed adhesion.

@LeoErvin I could be misinterpreting your comment, but I don't think an ABS slurry is meant to stick directly to the build plate. Usually the acetone in the slurry helps break down a bit of the Kapton tape (for ABS printing), allowing the slurry to bond easier to the surface of the tape (maybe the microcracks you mentioned?). Then, as the HBP heats up, it creates a more native surface for the ABS to bond to.

@tbm0115 I don't know what acetone does (or doesn't do) to kapton, but what I described is the reason abs slurry sticks to bare glass so well. The mixture is far less viscous so it can get into tiny cracks in the glass. However, once the acetone evaporates, the printed ABS sticks to the ABS left from the slurry which itself is stuck to the build plate much better, hence why ABS slurry helps so much with glass beds. This is the reason why ABS left from evaporated slurry is so much better stuck to the glass than an ordinary 1st layer which can easily lift.

Add your settings if you want a good answer.
Following. Increase raft seperation distance, and buy simplify 3d?

A couple things to consider:

Ensure that your build plate is flat and level. An un-parallel HBP could result in the object "welding" to the raft.
Turn down your nozzle temperature. It is likely that the material is hotter than it needs as it is extruding. This results in a slower "cool-down rate". So, if it takes longer for the filament to cool between the raft and the first layers of the object. Therefore, cooling together in a manner that somewhat binds them.
Personally, 266C seems VERY high to me. I've primarily only used ABS on my MakerBot and have successfully printed with 225C +-5C nozzle temperature and 110C +-2C HBP temperature.
Typically you want to extrude slightly above the melting point. You don't want to liquefy the material, but make it pliable enough to bond it to other layers of material (or a BP).

You could try reducing the temperature of the hotend. If you are using too high of a temperature, the ABS will "run" and over-adhere to the raft.
What slicer are you using? I have found that raft quality is drastically affected by the slicer I've used. In my experience, MakerBot and Simplify3D produce the nicest, easiest to remove rafts. I've also had success with Cura.
Barring changing the temperature of your hotend or switching to a new slicer, you could always try printing without the raft. From the sound of it, your bed is hot enough. Do you have Kapton on the bed? If so, give printing without a raft a shot. If sticking is an issue, try painting a slurry of ABS and Acetone onto the bed before starting.

Do you allow the filament to cool completely (5-10 minutes or longer after printing) before you begin to remove the rafter, or do you remove the printed piece immediately after finished printing and begin to remove the rafter?
In my experience, I have noticed that the rafter is easier to remove if the piece is still somewhat warm from the heated bed.

I haven't got a printer with a heated bed so have only tested this on PLA but I have found editing the G code so the printer cools the nozzle down and then heats it up again gives the raft enough time to cool down so that it peels off easier when the print is finished.


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Running 12 V on a 24 V heater cartridge?
Would I damage anything running 12 V on a 24 V cartridge heater? I know it wont reach a max temperature 300 °C? I am using the E3D hotend set up.

Applying 12 V to a 24 V heater cartridge won't damage anything, but you may have severe issues reaching and maintaining your target temp. A standard E3D heater cartridge is 40 W. When you run a 24 V cartridge on 12 V, you only get 10 W of heater power. Here are some rough estimates on where your hot block heat goes:

Uninsulated hot block air losses: ~20 W depending on airflow
Insulated hot block air losses: ~5w depending on airflow
Filament melt power at typical print speeds: 0.3-3 W depending on filament and print speed
Heat conducted up the heat break: 1-3 W maybe, hard to quantify

I've never heard of anyone using less than about 16 W to print. (Two 8 W power resistors.) 20 W is the lowest vaguely normal hot end power. I think you'll struggle to print.

10W would work if you print a material that melts around 80-100°C, like... Hot glue


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Efficient and easy way to thermally insulate the heat block of the hotend?
Sparked by this question, I wanted to discuss the most efficient and also the easiest ways of thermally insulating the heat block of the hotend.
I have seen Kapton tape insulations as done here with a very conclusive resumee about its usefulness.
In the links of the named article, a method with insulating material from a heatbed is described, however without giving quantitative results.
Additionally, I know that in the guys over in the german reprap forum produce their own silicon covers for the heater block. As I understand there is a large spread between people's reports, from 'almost negligible' as insulator (but helpful for other things) to very useful. No quantification, though. Also, these seem to come with a certain amount of effort to produce.
Are there additional solutions and/or comparisons between solutions?

The "quick and dirty" approach is to just slap a bunch of Kapton tape on there. The more the better! (Until you need to dismantle for maintenance, anyway.)
I find pre-cut ceramic tape + kapton tape "blankets" to be easy and effective. E3Dv6 and Replicator 1/2 style hot blocks should be compatible. Or you can cut your own using a sharp hobby knife.

http://www.fargo3dprinting.com/products/makerbot-replicator-2-ceramic-insulation-tape/
The main downside is that they don't insulate two sides of the hot block. But covering the top and bottom provides much of the practical benefit, and you can always add a few more wraps of Kapton tape to cover up the rest of the surfaces.
Another good option that has recently started to become popular is fiberglass heat shield tape. It has a silicone adhesive, woven fiberglass mat, and shiny aluminum surface. (The reflective surface reduces heat radiation.) It's often used in automotive applications around mufflers and the like. You can cut it up into little rectangles for each side of the hot block, or wrap the block similar to Kapton.

https://shop.raffle.ch/shop/insulation_material/
Main issue is quality -- not all brands have adhesive that will hold up to high temp printing. It may smell when initially "burned in" due to the adhesive cooking a bit. I also find that you need a couple layers to get as much insulation as the ceramic+kapton blanket when there's a lot of airflow around the hot block.

I know it's a bit OT but i use this second material under my heatbed which increased a speed of heating up HB more than 2 times

Oh yeah, I do the same thing. Works great for heatbeds in unenclosed printers. (I WANT the heatbed in my enclosed printers to heat the air!)

These premade kapton insulators with fiber look good. Do you have any quantitative results like heat-up curves with and without such an insulation? This and also the fiber material given in you second solution are basically what is described in my second reference link, or do I miss something?

If I'm understanding his description correctly, he used Teflon sandwich toasting bag material under the Kapton. I haven't personally heard of that. More common to see either the white ceramic tape or just multiple kapton layers.

Did you ever make some quantitative measurements on your insulated heater block? Power consumption, pid temperature variation comparisons for example?

Watching trends and power levels and stuff... not much quantitative logging. I got a 4-channel thermocouple package recently and plan to do some benchmarking of different hot ends.

I ask myself why people hassle with kapton tape when it is so easy to use teflon sealing tape to isulate the hotend. This tape is slightly foamed to allow better sealing when used for sealing "tube threads". It can be purchased anywhere for very little money and can stand up to 260° Celsius constantly and 300 ° for a short time (according to its data sheet) This shoud be sufficient for most applications. Water installation PTFE tape is very easy to apply because its soft and can be stretched to the right form. And it sticks for its own without extra glue. No hassle like with the stiff kapton tape. And the isolation is much better because of the air bubbles inside the tape. I did that on my extruder and it works perfectly. My extruder heats now up about 20% faster. I applied this tape in installed position within 5 minutes - easy !

Welcome to the forum!  I like your idea to use plumbers tape, and I'm sure I will try it.  This answer doesn't directly address the OP's interest in comparisons, but it is on-topic.  Could you improve the answer by comparing it with your experience using other insulating methods?

Sounds like a great idea, but is there any issue with the toxicity of the fumes (even if no odor)?  Just curious.

@Questor , this is indeed an issue with PTFE tape: https://en.wikipedia.org/wiki/Polytetrafluoroethylene#Safety It starts releasing some non-great stuff at 200C, and increases with temperature. In the study cited by Wikipedia, the amount isn't worrisome until 250C, but this isn't a frying pan...we run these things at temperature in enclosed spaces for hours/days at a time. So I avoid PTFE in contact with the heater block, but it's in an abundance of caution.

I am using high temperature RTV. I just load it up and smooth it out like frosting a very small cake. I leave the top of the heater block clean and cover it with a piece of cotton insulation. I don't care about power consumption, I just want it to stay hot when the workpiece cooling fan comes on.

I've had good results with "high temperature gasket maker", which is quite similar.(for example https://www.permatex.com/products/gasketing/gasket-makers/permatex-high-temp-red-rtv-silicone-gasket, good up to ~315C). Since you just squeeze it on and let it solidify, you can cover any shape, as thick or thin as you want. You can trim it or peel it all off if you need to later.

I just came up with my own solution before I read this discussion. (Monoprice Select v2.1 - Wanhao i3 Clone).
I ~think~ I have a Mk8 hotend.
I had some silicon rubber sheet (about 1.4mm thick) which started life as a cookie sheet, but I gave it a new purpose in life, LOL.
I cut two pieces to length to wrap around the hotend, and made a double thick sandwich.
I then used adhesive backed aluminum ducting tape* (SEE EDIT BELOW!!) (NOT duct tape, ALUMINIUM tape) and wrapped the sheets in it, then used needle nose pliers to shape it to fit the heater block. The aluminium tape helps it hold shape.
I used 3M 468MP to tape it to the hotend, as I currently have no kapton tape.
Just did this today, if I have adhesion issues I'll TRY to remember to report back here. :) If it does pops loose, I'll use a bit of stiff wire twisted around to support it.
EDIT: Welllll ... sometimes one gets too clever for their own good!
USING THE ALUMINIUM TAPE IS NOT A GOOD SOLUTION, DON'T DO IT!!! It seems the adhesive on that tape emits noxious, and perhaps POISONOUS fumes when heated! I had to vent the room to the outside for a couple hours with dual fans and the hotend at temp to clear the air! Ooops. LOL
It's good now, it baked off.
The idea DID work, and I'm sure would be fine if you use regular heavy duty aluminium foil. Be sure to mount it with the seam on the INSIDE and the 3M tape should hold it closed just fine.

You can quantify the improvement by timing how long it takes to heat from cold to 90 degrees (with a target of 100, so there is no control loop input).

@SeanHoulihane - Yeah, that makes sense, thanks.  I noticed a huge improvement on the BED when I installed two cork sheets (with a notch cut to clear the wires) under it, again using the 3M 468MP tape. Heatup time dropped considerably and it's much more stable. Of course it also cuts cycling so saves energy, reducing load on the power supply.

Heating up aluminum is might not a great idea (even if it is tin foil) due to the extreme temperatures...Aluminum fumes are linked to Altzhiemers(sp?) disease (though I cannot say where the safe vs. unsafe temperature range is since it must be okay to some temp since it is widely used in cooking).   Not really sure how much of an issue it is but just tossing it out there as something to consider.

@Questor: Heating aluminum does not produce fumes. Just cooking things in aluminum is a problem. (Note that the whole heated block of most hotends is made of aluminum).

Perhaps fumes was a bad choice of words, but heating aluminum increases aluminum oxidation, which is bad.  Of course the thickness of the aluminum and the temperature also come into play, but there is no doubt that there is an increased oxidizing effect of heating aluminum, and bad side effects such as Metal Fume Fever (amoung many others):  https://en.m.wikipedia.org/wiki/Metal_fume_fever

After having seen this answer to this question, How can I insulate my thermistor?, I ordered these, from eBay, 5PCS 3mm Thick 3D Printer Heating Block Cotton Hotend Nozzle Heat Insulation EW, for around £0.40

Blurb from the item's description

Thickness: 3mm
Dimension : 75mm*21*3mm +/-0.2mm
The heat insulation cotton is used for 3D printer nozzle keeping warm;
The heating insulation cotton is made from heat-resistant ceramic fiber;
The product sizes can be customized according to customer needs;
The benefit for keeping the key parts of the 3D printer heating aluminum block warm;
Is making the internal temperature flat, saving power,and energy;
This High temperature resistant cotton can work for a long time in high temperature of 900 degree.

Other images:

Granted, these look suspiciously like the strips in Ryan's answer, but use cotton, en lieu of ceramic tape.


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How to choose an extrusion temperature?
From what I've been able to find out, online sources recommend around 205ºC for PLA and around 240ºC for ABS. But these are only guidelines, of course. Optimal printing temperature can be different depending on the printer, the filament, the model and other slicer settings.
For example, I've had success printing black PLA at 190ºC, but silver PLA of the same brand is giving me trouble. I'm having a hard time figuring out the general rules. So I would like to see a general guide for this, based on (at least) the following questions:

Which known factors before a print can help determine the right extrusion temperature? Obvious example: ABS vs PLA
What can happen during or after a print when the temperature is too low?
What can happen during or after a print when the temperature is too high?

An answer to the first question could take the form of a lookup table, or similar. The second and third could help someone adjust their temperature based on the symptoms of a failed print.
I understand that the failure or success of a print can depend on many more factors than extrusion temperature, but I didn't want to make this question too general. I may later ask the same question for other settings (e.g., print speed). However, do let me know if this question should be expanded or improved to make it more useful.

Printing temperature basics
Manufacturers generally specify a somewhat wide range of printing temperatures, and what temperature you should actually need can only be determined by trial and error:

The thermistor in your hotend is not 100 % accurate and may have an offset of a few degrees compared to its actual temperature.

Your hotend has a small temperature gradient, the place where the plastic is melted may have a higher/lower temperature compared to the temperature of your thermistor.

2 is further exacerbated by

As you print faster, you need more heat. The cold filament rapidly moving through your hotend will cool it down locally, meaning that the temperature will be cooler than what the thermistor measures. Faster prints equal bumps in the temperature up to 10 °C, and for a really slow print you might turn it down 10 °C from where you normally are.

This is a minor issue, but different colors of the same brand and material might work better at different temperatures. The pigments used can affect the melting point somewhat. Different brands also might have different temperatures.

Some symptoms may give you a guide as to how to adjust your temperature:
Printing too hot

Small/slow prints may not solidify quickly enough, leaving you with an ugly blob.

Stringing/bad bridging.

Plastic in the heatbreak may soften, leading to clogging.

You might burn/degrade the material (but for this you would really need to go outside of the temperature range).

Printing too cool

Too much force required to extrude, leading so skipping/grinding of the filament drive.

Layer delamination: the plastic needs to be hot enough to partially melt the layer below it and stick to it. Objects printed at a colder temperature tend to be weaker at the layer boundaries.

Furthermore, hot prints can sometimes have a more glossy finish than colder prints.

Very useful, thanks! By any chance, are you aware of a specific 3D model that may help a person find their optimal temperature? Like, a model with certain characteristics that are particularly sensitive to temperature?

@mhelvens Given that the ideal temperature depends on the model you're printing, such a model does not exist.

Fair enough. ;-) But the reason a temperature may fail for a specific model probably depends on specific characteristics, like overhang, bridging, sharp corners and the like. I was imagining a model that has all of those characteristics, and could help you understand the 'temperature space'.

Some manufacturers give a recommended temperature which would be the best place to start at and adjust from there. Otherwise you could print calibration objects and find the best temp that way. Here is a temp tower for that purpose. Mostly it is a trial and error process with all the different printers out there. What might work on one printer may not work on another.
The object may come apart if the temperature is too low as the plastic won't bond well between layers. You may also get a rough surface on the object and the filament may also jam in the hotend as well.
Normally temperatures that are too high, your bridging wont be as good and you will get a lot of stringing. Stringing example, more filament will ooze out before retracting if your temperature is too high. Your overhangs may also curl at the edges as well.