text:
Filament lifts from the hot bed while printing
I have a Tevo Tarantula 3D printer.
I'm trying to print a calibration cube.
The slicer is Cura and is set for a 1.75 mm filament extruded by a nozzle of 0.4 mm, with a heat bed temperature of 60°C and extruder 200°C.
As seen in the image I stopped the printer after a minute, when I noticed that the filament wasn't sticking to the hotbed.

I've also made other tests, but the result is the same - the upper right part of the print lifts and touches the moving nozzle.
How could I resolve this? Any advice?

Is the print bed clean? Is the print bed actually reaching the correct temperature? Have you manually calibrated the printer (at both the center and the edges), such that you can just about get a sheet of paper between the print bed and the hotend nozzle, at z = 0? This last check ensures that the first printed layer of extruded filament is actually touching and "presses on" to the print bed. Maybe the filament, for the first few layers, should be heated at a high temperature, than the rest of the print, to ensure adhesion.

The bed should reach the correct temperature, that is measured by a thermo resistor and displayed on the printer LCD as 60°C.
Yes, I've manually calibrated the printer, maybe I should check again doing this trial with a paper sheet.
A thing that I didn't do was to clean the bed, maybe this should do the trick.

What kind of filament are you printing? What is your first layer hight? What is your layer pattern? Did you clean your print bed with something to remove fingerprints, dust and oil?

Check the following:

Is the print bed clean? On glass, you can use a few squirts of window cleaner.
Is the print bed actually reaching the correct temperature?
Have you manually calibrated the printer (at both the center and the edges), such that you can just about get a sheet of paper between the print bed and the hotend nozzle, at z = 0? This last check ensures that the first printed layer of extruded filament is actually touching and "presses on" to the print bed. See the video #18:Calibration for a great explanation on the use of the paper. Whilst this video is for a Delta printer, it clearly demonstrates the height that the zeroed print head should be at, and how to check using a sheet paper.
Maybe the filament, for the first few layers, should be heated at a high temperature, than the rest of the print, to ensure adhesion.

If all of the above are checked and OK, then (as electrophile points out in their answer) try making the print head more grippy. This can be achieved by simply adding a thin coating to the glass with one of the following:

Wiping the glass with a glue stick or wood glue
Using hairspray

Both use PVA as an adhesive/stiffener.
Or by adding an additional print surface, such as:

Using blue painters tape
Using PEI tape
Using Kapton tape
Using BuildTak

If adding tape, then the printer may require a small re-calibration, due to the thickness of the tape adding a few microns to the print bed height. This can be done in the firmware.

I don't have this specific printer but this used to happen to me as well on my D-Bot. The reason being bed not being leveled properly. Ensure that your bed is leveled such that the distance between the nozzle and bed is about 0.2mm after homing. Also coat your bed with something sticky like glue or hairspray. You won't need this if you are using a PEI sheet.

I've cleaned the heated bed as suggested using ethanol,
then I've tested the Z distance of the nozzle from the bed with a paper sheet and it was ok. Lastly, I tried to raise the temperature of the extruder for the first layer to 215°C. I think that this did the trick.

With PLA I normally run the bed at 70 and the extruder at 190. Make sure the bed gets to temperature before you start and use gluestick on the bed.

material sticking problem can be due to following reason:

bed level
bed temperature
z motion calibration (ex if not calibrated layer height is 0.2 and z move 0.4 then material cant stick on bed)
bed surface (for sticking first layer on bed what you use)

remove all above reason step by step

first confirm bed level
bed temperature according to material (pla - 70 , abs - 100 )

all above option are good but warpping chance are higher
for last bed surface you have following option to use

use paper tape
use Kapton tape
glue stick
use paste  (accetone + abs) abs melt into accetone and it become like cream and you can apply on bed after bed heating

if you are using last option then just confirm bed level again before start print


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Is there a G-code to get power supply state?
I'm using M80 and M81 G-codes to power on/off power supply.
Is there a G-code to know the actual state of the power supply?

While there is no dedicated command for this, there may be some options.  Can you describe your hardware?
Are you using a stock printer or a custom?
What are you turning off with the M81?
Are you just turning off the 12V and leaving 5V board supply on?
What boardset are you running?  RAMPS?

Thanks! I confirmed that there isn't such a G-code.
I sent a pull request to make this posible:
https://github.com/MarlinFirmware/Marlin/pull/6671
Now, "M80 S" reports the current state of the power supply.

I don't see one at http://reprap.org/wiki/G-code so it's probably safest to set the power supply to the state you want.

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How can I insulate my thermistor?
I have had many problems with my heat shrink for the thermostat on my Anet A8 melting from the heat block.
Is there a way I can insulate my wires from heat but still have enough room to put the thermistor into the block?

I've added another photo to my answer, that you may find very useful.

For an illustration of how to employ the Kapton tape, that is mentioned in the answers from Harvey Lim  and Howler, watch How to build a RepRap Prusa i3 (Assembly 7) at 21:30:

From 15:10 the heater and thermistor is connected up, you may find this also useful. Note that, at 20:45, the heatshrink is only used over the soldered connection, and not all the way up to the heatblock:

Also, more pertinent to your printer, from Anet A8 Review – Best cheap 3D Printer?, see that the thermistor wires are also wrapped in Kapton tape in this photo:

Note that the Kapton tape is wrapped around the wires, almost right up to the thermistor, and will be touching the heating block, when the thermistor is inserted into the hole - there is no problem of it melting, due to its high melting point.

You can use kapton tape, small PTFE tube, or silicone tape. I use PTFE on my delta printer (I do have a silicone tape wrapped around my heat block, but that's to help with keeping the heat in the block, not for eletrical insulation (although it would work for that)). These will all handle the temperatures of your heat block fairly well.

I was thinking about getting a custom fibre glass part made. Do you think this is worth it? Many thanks, Thomas

I was going to go with PTFE but it only goes up to 204C so I'm not sure now... Thanks for all the help though

You could use Kapton tape to tape the thermistor. It is usually the best option for sticking something onto the hotend or on the heat block. You will also have less trouble since it is very thin.
Note that if you use Kapton tape, you should use several layers of it for added insulation.

So it will not melt on the heat block?

Kapton should be good to 400 °C but your mileage may vary depending on where you bought it.  The Ebay special Kapton may just be orange tape, who knows...

Well it can melt...its just no hotend on this planet could get hot enough to melt it. As @tjb1 said, it melts at 400 °C.

Ok, so I think I have found the answer. You can get cotton wraps for print heads with some Kapton tape on them, see 10Pcs 3mm Thickness 3D Printer Heating Cotton Hotend Nozzle Heat Insulation. I think this will work best as long as it doesn't catch on fire.
Please let me know if there is a better alternative but for now I will use these.

authors: เอ็ม เอ็ม เอ็ม

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Would using a leadscrew with 1 or 2 mm lead, en lieu of 8 mm, result in a better printer?
By "better" I mean "more precise"...
With respect to a RepRap P3Steel or Wilson II, I am getting some 330 mm T8 leadscrews for the Z-axis movement.
There seems to be a choice between a lead of 1, 2 or 8 mm - the pitch is 1 mm in the first case and 2 mm in the last two cases1. However, there is precious little information about the advantages and disadvantages of each lead size in RepRapWiki - Threaded Rod - Leadscrew.
It seems to me that using a leadscrew with a 1 or 2 mm lead could result in a more precise Z-axis movement, as one rotation of the stepper results in a smaller increment in height. Therefore the layer thicknesses could be smaller.
However, is the minimum layer thickness not, also, dictated by the thickness of the filament, horizontal speed of the print head, nozzle size, etc.? Thus, at some point there would be no need for a super fine vertical resolution from the leadscrew, as it may be constrained by other limiting factors.
Of course, conversely, the use of a 2 mm lead would mean that the stepper would need to "work" four times as hard, than when using 8 mm, in order to raise the print head the same distance, as well as making the movement, during a "home", take four times as long (or, if you will, four times slower). In the case of a 1 mm lead that would become eight times...

TL;DR
Is it worth getting a leadscrew with a 2 mm lead, or is 8 mm sufficient?
By extension, would a 1 mm lead be even better, or just overkill?

Footnote
1 Nomenclature:

Pitch is the distance between the adjacent threads;
Lead is the distance that a nut will turn with one rotation, and;
Start is how many starting (or thread entry) points at either end.

So, for a leadscrew, with a pitch of 2 mm, if there is only one start to the screw then the lead is the same as the pitch. However, if there are four starts to the screw, then the lead will be 8 mm. If there are two starts to the screw, then the lead will be 4 mm. And so on.
For more information, see Wikipedia - Lead, pitch and starts.

Based on what I've learned over 8 months of printing:
What matters the most is getting a very accurate zero relative to the bed surface.  An offset of 30 or 40 microns can strongly affect first-layer adhesion.  Now, unless you put in some of the advanced auto-levelling sensors, the repeatability of the Z-axis limit switch may outweigh the precision of the lead screw itself.  But if you've got a good limit sensor, then the more precision in the lead screw, the better you can set (and repeat) the position of the first layer.
I don't see a significant difference in strain on the drive motors if they have to run longer per mm of z-drive - just make sure the lead screws are clean :-)

W.R.T. the strain on the stepper, it appears that the 8 mm lead will require more torque than the 2 mm lead. So, the lower the lead, the less torque is required. From Accuracy vs Precision and Threaded Rod vs Leadscrews in 3D Printers.

From Accuracy vs Precision and Threaded Rod vs Leadscrews in 3D Printers. I have highlighted the relevant parts:

In general, FFF/FDM printers use relatively infrequent, small, precise
movements on the z-axis and consistent, fast movements on the x and y
axes. A single start leadscrew with the tightest pitch possible
(highest thread density, smallest pitch) is generally going to be your
best bet for the z-axis, while you may or may not need something a
little steeper to get the speeds you'd like from your x and y axes.
While this may seem somewhat arbitrary given the precision of movement
you can get from a stepper motor, an important factor to remember here
is torque.
A more aggressive leadscrew will require more torque to drive. We have
one kit printer we bought a couple years ago that has an overly
aggressive multi-start leadscrew for the z-axis. The small motors
included in the kit do not have the torque required to reliably start
upward movement of the carriage, leaving it sitting there skipping
steps until the carriage is given a little upward nudge to get it
going (no, it's not a lubrication issue or a driver that needs turning
up).

So, a 2 mm lead is preferable to a 8 mm lead, as not only is less torque required, but also more precise movements are obtainable.

With respect to the layer heights, I found this nugget of information, from Ditch the threaded rod in your RepRap 3D printer and upgrade to a lead screw z-axis

It's always better to use layer heights that are a multiple of your
full step. If you trust in your micro-stepping you will get poor
results because torque is very poor and the motor won't stop very
precisely. Best approach is to use a lead screw (whose longer step
allows the gravity to work for you and eliminate backlash) and a
stepper driver configured to 1/4 micro-step for low noise, but not for
micro-layering. I always use multiples of my full step and have
printed 0.040 (1 step), 0.080 (2 steps), 0.120 (3 steps and so on), 0.200,
0.600 and 0.800 mm (of course using 2 different nozzles). Do you need
more than that?

See also Reddit - Lead screw opinions

the general consensus is that a 2 mm lead is preferable to a 8 mm lead:

Lower the lead the better for an Z-Axis screw to allow for more precision.
No need for anti-backlash nuts for a Z-Axis if it has a decent amount of mass/weight to it.

1 mm will slow the printer down, but provide 0.005 mm (5μm) vertical movement:

That's going to be awfully slow when homing. While you really don't
need speed for the z-axis, there's not much point in going with such a
low pitch... you won't be printing anywhere near the layer heights
that can achieve. In the end I guess it's not a big deal, but I don't
see any reason to go below about a 4 mm pitch. A 1 mm pitch with a 1.8°
stepper gives you 0.005 mm increments. Anything under 0.02 mm (which is
sort of ridiculous anyways) is just unnecessary. Just my thoughts.

(As Tom points out) An 8 mm lead can result in the weight of the X-axis gantry (especially in a P3Steel) overcoming the idle torque of the stepper. As a result of this, the X-axis gantry can end up sliding down the leadscrew, in particular at power down:

I have lead screws on my Z and it readily falls down if you kill the power. Regular threaded rod is much better at keeping it in place without power.

and

That's one of the problems with 8mm lead ;) With 2mm lead it will hold itself. The stepper motor provides a fair amount of resistance even when powered down.

TL;DR
Be wary of leadscrews with a lead, as opposed to a pitch, of 8 mm, as there are disadvantages, when compared to a lesser lead of, say, 4 mm, or 2 mm (or 1 mm for leadscrew with a pitch of 1 mm):

Higher torque may be required
Less accuracy
Possibility of slippage, of the X-axis, once power is removed, or stepper is disabled1
Anti backlash nuts required

However, their major (if you can call it that) advantage is a higher maximum movement speed.

With regards to the "less torque" part: with an 8mm leadscrew, the weight of the printbed or carriage can overcome the (idle) torque of the stepper, causing the bed or carriage to drop like a rock when the stepper is disabled. This can be rather annoying.

@TomvanderZanden - Yes, that is a very good point. Some users in the Reddit thread have made mention of that... especially at power down. I have updated my answer.

Longer lead
Pros:

Faster movement (mostly benefits homing)
More standard
Weak motor friendly
Might be slightly more stable (sideways) than shorter leads because of more starts creating more contact with nut (?)

Cons

Backlash
Less resolution (unless using 0.9 degree motor but see note1) although this is ignorable since it's still very high. It's already around 5x higher than xy axes using the longest leads2.

Shorter leads
Pros

More accuracy if you turn off microstepping. it can give you more resolution, but it's useless resolution unless you print with < 0.01 mm layer heights3. Turning off microstepping trades away this useless resolution for increased accuracy. But this comes at the cost of (much) louder drivers.
Less backlash

Cons

Stronger motors maybe needed
Slower homing

The reason why companies prefer longer leads is because shorter leads simply add useless resolution and slows down movement.
Footnotes
1 It makes more sense to use higher degree motors to drive shorter leads than vice versa because of higher torque.
2  0.0025 mm vs 0.0125 mm
3 or using a probe to autolevel, which causes the z axis to go up and down in very small increments

Wouldn't a shorter lead, meaning more steps per z distance, equate to less load on the motor and allow a smaller motor? Basic gear ratio stuff says that would be the case. I'd like to hear the rationale behind the contrary. An 8 mm lead would be equivalent to being in 1/4 final gear ratio compared to a 2 mm lead - equivalent to driving in a higher gear (4th for example, instead of 1st). So a shorter lead is slower, transfers more torque, and the motor is spinning faster for a given movement. To further explain, basic mechanics dictates that the motor have to

work harder to lift the x axis by 0.04 mm per step, than 0.01 mm per step

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Continuing a failed print when you have Auto Mesh Bed Leveling
When you have Auto Mesh Bed Leveling enabled on your printer, it's not possible to continue a failed print, is it?

Continuing a failed print has nothing to do with automatic bed leveling. It has everything to do with knowing which line failed, repositioning to resume from that point, and resuming from that line of code.

but you won't be able to do a g29 because your half printed part will be in the way. Will it not be slightly off the z axis?

You may be able to G29 the surface of the print; my printers don't do G29; we set the Z manually. I would make a copy of the file, strip out the moves already executed, insert a G92 Z## where ## is the present Z position, and restart the print from there, with this edited file.

I'm not sure this answer is right. The printer will no longer compensate in the same way, so if your bed was really tilted, the newly printed layers won't be in the same plane as the original layers.

@Ageis The compensation of the shape of the bed when using ABL is only active for a few mm's of your print if it has #define ENABLE_LEVELING_FADE_HEIGHT enabled. The height can be set with M420 Z<height>

So like resuming any print, if you've already done the work to find the layer you failed at, edited the G-code to start from that layer. But now you feel stuck because to start a print you need to home your printer right? And homing with a BLTouch makes it probe the center of your bed... which happens to be where your print is at. IF you're on Klipper, you can put something like this here:
[homing_override]
set_position_z:0
gcode:
 G90
 G1 Z10 F600
 G28 X Y
 #G1 X161 Y125 F6000 ;old bed center
 G1 X245 Y215 F6000 ;far right corner of the bed. You may have to adjust your X and Y for your BLTouch location as mine is on a Hero Me hotend
 G28 Z
 G1 Z100 F24000 ; move Z-axis up so hotend doesn't hit the print when zeroing. Adjust this as needed to clear your print from where it failed
 G1 X0 Y0 F24000

And from there, the printer should Home and you can start your partial G-code from here. IF YOU HAVE KLIPPER. Make sure to remove any purge lines or stuff like that from your Start Print code.


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Choosing the most high quality, reliable 3D printer
I work in a biological laboratory where we have been using the FABtotum personal fabricator for several months now. The machine is good, however not flawless, and has set us back from doing experiments.
I have overcome many common 3D printing issues, which I find necessary to do when becoming proficient in this technique. However the printer has also had its own personal mechanical and software issues.
Our lab is seeking a printer that is more reliable, can produce parts relatively quick, good resolution, and it is nice if it has multiple modes (i.e FDM, SLA, and even 3D scanning is nice). This is what we figured we were getting with the FABtotum, but as I mentioned it has produced setbacks.
Now I would love to tinker with the printer and modify it to my needs, but unfortunately our lab is strapped for time, however we have funding for a higher quality printer if there is one.
Can you anyone recommend a printer fitting these needs in these budget categories?:

3000 USD
5000 USD
8000 USD or more

I know price doesn't equate quality, but I am saying that we are willing to pay more if that is where the quality lies.
For example, I have come across the Form 2, Ultimaker, and BCN3D sigma printers which seem quite nice. Any opinions are very appreciated.

This question is asking for people's opinion which is great and believe there are many people here that have them (opinions).  Stack Exchange has however, chosen that it doesn't want to be the place to ask those types of questions.  Maybe is it because it is intended to be a resources for answers and when a question is opinion-based, there can really be no right answer.  For more info on this, look at https://meta.stackexchange.com/questions/201994/is-there-a-place-to-ask-opinion-based-questions

Well thanks for that. In my case it is a matter of setting back biological science or the forum could help accelerate it. This is why it is a shame that I cannot get this sort of opinion from an experienced base of people on stack exchange.

In that case, where should I ask this type of question?

I hear your frustration, and your are not the first.  It seems this exchange seems a bit more lenient on those rules; so, maybe you will get the info you are looking for.  For me personally, I have a kit printer - the opposite of what your are looking for.  At work we have a Stratasys Polyjet.

You could specify your requirements in a post at http://3dprintboard.com They are always quick with advice.

@theguy0 The primary reasons that StackExchange limits the "suggest me a shopping list based on my criteria" questions are: 1) generally, they are not useful to others who do not have the same constraints or needs as you do, and 2) they quickly become stale and there's no built-in mechanism to keep them up to date.

At work we have a Stratasys Polyjet.  It prints using UV cured gel; so, it is kind of a cross between FDM and SLA.  I have not used it personally, it is mostly used byt the ME group.  The parts I have seen that it produces are VERY good and it support different materials and even multiple materials.  They have a lot of different product levels so they can support different price points.  The only complaint I have heard is the material cost.
It can print some amazing stuff
Here is a nice video https://www.youtube.com/watch?v=HMMJnn_gHWw

I have only tried 2 different printers. I started with an Up plus printer and it was good to get started. After a few years you really want more control. I did a lot of research and ended up buying the Extrabot. It is based on the ultimaker however the guy that puts them together upgrades the motors and a few other parts to really make them work with multiple filament.
You have control over all the settings so using exotic filaments is a viable option.

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authors: هلال العتيبي


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Bed Adhesion materials
There are all sorts of stories of what to put on your printer bed to make your part not come loose when it is printing but can be removed after it is done without requiring a hammer and chisel.
Is there anything out there that shows an analytical comparison?
My biggest interest is PLA on a heated glass base.

You are printing with Medium Density Fiberboard?

Thanks, I was just answering a question on MDF and all the TLAs (three letter acronyms) must have gotten scrambled in my brain.

I don't have an answer to your question, which is a link to an analytical comparison. I suspect you'll get plenty of anecdotal suggestions similar to the first one posted. I'm all for 3M blue tape but it sticks harder when cool. I tend to dribble a bit of 50/50 mix of denatured alcohol and water around the part and it releases nicely when warm. Works even better on PEI film on a print bed.

There are certainly a lot of anecdotal suggestions out there and those are helpful; but it would be really helpful if there was something objection.  Anyway If I asked for suggestions, wouldn't that be an "opinion based" question?

A friend that does a LOT of 3D printing swears by glue stick.

I use a product called 3DLAC but I suppose it's regular hairspray. Makes my PLA stick to the heated bed like a charm. After cooling down the print can be removed from the bed with ease.
Only today, after a few thousand prints the glass bed of my printer broke. But I suppose this is because we didn't have enough patience to let the bed cool down to room temperature before removing the printed piece.

If you can upgrade your bed to a magnetic bed with spring steel top all the problems of breaking parts loose go away, the method is you take the spring steel plate off the magnets and twist it gently to allow your part to break loose.
There is a commercial product going under the name MagHold. I am not affiliated with them but really like the idea and have it on three of my printers, works great.
For best results overall I recommend PEI material on top of the spring steel plate. the PEI works great for PLA at 50°C and PETG at 80°C. And you can still break both materials loose easily by twisting the plate. No damage to the sides of your parts from prying.

I already spent time reading up on this and quickly worked out there is a lot of useless products out there. Sure they may work however it adds a massive cost to your print.
What I have found works best for heated glass beds is Glue stick, nice and cheap, lasts a long time and has never let me down. Bed temperature is also very important to get right however out of all the products I have tried, Glue Stick works the best.

And you can clean it off with ordinary isopropyl alcohol when it gets uneven and easily re-apply.


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Regarding the E-step in Cura
I'm using a Delta Wasp 2040 printer equipped with a clay extruder. I'm using Marlin firmware.
I'm trying to print food (vegetable creams) not PLA filament, but my question is about the setting of some of the parameters.
As reported in Marlin, the default values for X, Y, Z, E axes are:
* D e f a u l t A x i s S t e p s P e r U n i t ( s t e p s / m m ) * O v e r r i d e w i t h M 9 2 * X , Y , Z , E 0 [ , E 1 [ , E 2 [ , E 3 ] ] ] * /

#define DEFAULT_AXIS_STEPS_PER_UNIT { 80, 80, 4000, 500 }

My questions are below:

The value 500 is intended as mm/min. If so, the actual value should be 8.33 step/mm of filament in a time of 1 s. Is this correct?
It is not clear, in my mind, the E-step that I can change in Cura. This is what I believe:

If I leave in Cura, an E-step=0, then this means that I'm using the default value (500)?
What happens if I change the E-step value in Cura for instance at +0400? Is it changed from 500 to 400 mm/min, or the value on Cura is intended as a percentage of the default value?

Can you explain to me exactly how the E-step changes when modifying its value in Cura.

I can only weigh in on the Marlin side of your question - "The value 500 is intended as mm/min" - uh, no, AFAIK it's steps per mm, just like it says - i.e. with filament, 500 steps per mm of filament fed. Other than not allowing the feedrate parameter to go so high that steps are skipped (which is a different limit) it's time-independent. I suppose with an extruder it would be mm of piston movement, but I don't have an extruder.
In my case, an actual value is closer to 250, and I typically check the calibration with 50 or 100 mm of filament feed so I can make a decent measurement.
I also wonder if your firmware knows it's running on a delta, since mine reports "A, B, C" rather than XYZ and all three towers are the same steps/mm - the "default values" you are looking at might apply to a typical cartesian printer where the Z axis is threaded while the X & Y are toothed belts.
Assuming it runs correctly you might be seeing irrelevant "default values" and having correct values loaded from EEPROM when the system starts (look at the log window when the control system connects to the printer.)

authors: เณรแอร์ บางขัน


text:
Uses for PLA scraps
I recently got a 3D printer and have been experimenting with it a lot, resulting in a lot of failed prints (as well as successes, fortunately).
I'd like to, if possible, find a way to reuse the material from these failed prints.  I am thinking about two methods:

The obvious thing to do with the material is to chuck it in an old toaster oven and reuse it for injection molding.  Is this something that is reasonably easy to do? If so, what temperature would be reasonable to use? What materials would be good to use for the mold? (off the top of my head, silicone or printed ABS with some kind of sealant seem the most promising)
Are there other ways to easily reuse the material? I've noticed that when PLA is heated to somewhere around 50-60 degrees C (120-150 F) it becomes somewhat soft and malleable. Does anyone have experience molding hot PLA?

EDIT:
To be clear, I'm specifically asking about ways to reuse scrap PLA material, not just leftover filament, and not ways to turn it back into filament or to just recycle it. I'm particularly interested in the viability of the two methods I suggested, and if anyone has experience (positive or negative) with either I'd like to hear about it.

Possible duplicate: How to recycle filament material from printed parts? and What to do with failed/unwanted 3D prints?.

Possible duplicate of How to recycle filament material from printed parts?

Not a duplicate, though I might not have been getting it across well. My question is specifically about personal reuse, not recycling. Edited to try and add clarity.

Here is a great article on the subject, How to make your own filament by recycling old 3D prints | Part 1.
At $20/kg for new material, it is going to be hard for recycling to break even; but, if the cost is not your concern, there are some options.
Here is another creative option that I just saw... Cue amazing electric guitar riff:

Guitar Picks (and jewelry)

Here is the video: Failed Print Recycling Revisited // Guitar Picks, Earrings, and More.

A nice answer, but doesn't quite address what I'm looking for. I don't want to turn the waste PLA back into filament, I'm looking for other ways to reuse it. Thank you for the interesting links regardless!

I thought I covered both options - making filament and reusing scraps (be they filaments or parts scraps) by melting them into flat plates and them cutting them into jewelry or guitar picks.  IMHO, re-using PLA (unless you are talking LARGE quantities) will always require time and money (it will never be free).  Whatever solution will require a lot of passion regarding not throwing the scraps in the trash to justify the time and cost to re-use your PLA scraps.

That's part of what I wanted to address with my particular suggestions. While flat jewelry and guitar picks are easy to 3D print or make by other means, injection molding and hand sculpting can make things that are difficult or impossible to 3D print. I admit to not paying enough attention to the guitar picks link- it goes into more detail than I realized!

I ended up buying a little handheld 3D pen. It comes in handy when printing models that require assembly. You can use the leftover filament in the 3D pen. If you don't have a 3D pen, you can use a soldering iron (as long as you can control the temp) to weld items together. I works well for part repairs and assembly.
The 3D pens is also handy for quick simple prints, as mentioned above. A guitar pick is a good idea and very easy to make with the 3D pen.
As for making your own filament, there are a couple of machines I would recommend looking into.
First you will need something to prep the material.  This shredder will help.
To make your own filament, here are a couple of options

DIY
Off the shelf

Regarding Injection Molding, I have never done it, however found some good info on molding PLA.

A nice suggestion! Doesn't quite get at the heart of what I meant to ask, but a very good idea nonetheless. Regarding the soldering iron idea, what temperature would you recommend using? I do not have a decent soldering iron at the moment, but am in the market for one and this would be a good secondary use for it.

Your right, Sorry P. I updated my response for you.

Thank you very much for the updated response! The links were very interesting, and the last one in particular (while obviously more specialized than I may be able to use) is exactly the kind of thing I'd been trying and failing to find before asking this question. My Google-Fu is weak, I'm afraid...

hey P, I created a video here on getting the most out of Google. That should help you search Google a bit more.https://www.youtube.com/watch?v=Y1_ZbsMavE8&list=PL8BBKsD2COHs-qlBFK3w07zHs2oAav7AM

https://preciousplastic.com/ Is a fantastic project that promotes plastic recycling into useful objects. They offer free blueprints, videos on how to build the recycling equipment, and offer suggestions on what to make of your recycled goods.
Personally, I am looking into making garden bricks or paver stones. I have not found the ideal temperatures or heating methods just yet.


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Parts of my (apparently manifold) model aren't appearing in my Slic3r preview
I have an STL file that, when I load it in Slic3r, looks fine, but somewhere in the actual slicing process, something goes wrong and parts of the model disappear.

That's the render on the left, and the slicing preview on the right. That big hole is the most obvious fault, but there are more little notches elsewhere on the model; you can see a couple on the bottom edge there. It looks like the program is ignoring some of the model's faces entirely. What's all that about?
The model passes every manifoldiness test I've thrown at it: Slic3r's, Meshmixer's, Blender's, and a couple of online services I've forgotten.The walls that go missing are pretty thin, but they're at least a millimeter at their narrowest point, so I think it should be thick enough for the printer to handle.
Here's a link to the STL file in question, on FileHosting.org, FlashHovering.stl.

I fixed it!
I had my extruder diameter set to 0.5 mm, and the narrowest point of the model was just a hair under a full millimeter, so I guess the program took it to mean that it should only put down one line of material. I made the walls a little thicker and now it looks fine.

You should modify your original question or post your new question separately.

You should accept your own answer to the original question, in order to remove it from the Unanswered questions list - which, as we are a Beta site, we need to keep as small as possible if we are to graduate to being a full site. Also, your additional question, should be asked as a separate question. You can always link back to this question, in your new question, in order to provide more context.

Done. I got rid of the extra question - it seemed like it was a little too speculative to merit its own entry.


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Estimating printing time from Cura
I know that the actual printing time is longer than the time estimated by Cura, due to acceleration and jerk factor.
However, I have printed a small pyramid for which Cura estimates 4.0 minutes, while the measured printing time is 2 minutes and 40 seconds.
What reasons could produce this difference?
For clarity, I'm using a Delta Wasp 20 40 equipped with a clay extruder for which parameters such as E-step (for E axis) are unpredictable since I have no filament.

Related - this answer to Calculating the estimated print time of an already sliced file.

Have you found and fixed the problem? If so, have the answers below led you to the solution? Please vote to accept an answer (using the green tick button next to the question) so this question is not bumped up once in a while and can be removed from the unanswered question list. You may even add your own solution and accept that after 48 hours! If you have not been able to address the problem please update your question.

If you properly define your own machine with a delta_wasp.def.json file you can fill in the acceleration and jerk settings of your printer, so that Cura will use the correct values for print time estimation.
For example, take a look at how the Ultimaker 2 is defined.
Exposing these settings to the Custom FDM Printer wizard hasn't been implemented (yet).

Can you clarify which settings are used? If acceleration and jerk control are disabled in Cura (to leave machine defaults alone), what values are used for estimating? The machine limits? Or the set values of the disabled options?

The machine limits. Disabled settings are never used. It's these settings.

As you note, the estimates are usually optimistic because they're calculated without knowing the printer's actual acceleration as well as communication overhead time losses, etc.  However, many estimation algorithms put in a bit of a fudge factor to approximate a typical printer or to approximate startup time. I think in this case, you're just on the wrong side of the fudge factor.

Not true, Cura is just using the wrong acceleration and jerk settings. Cura doesn't use a fudge factor.

Estimating time for any CNC based machines are measured in this formula:
The length of pulses that machine travels x The feedrate of the pulse itself
It gives you the time for whole movements. If you're familiar with NC codes, information of any movement is listed in a single line, having its own feedrate, that's what we call pulses.
As machines are not ideal, some delay occurs between pulses, approximately 1 or 2 ms according to machine type. That's what is not measured in the formula.
If you were able to measure that delay time and multiply it in number of pulses, by adding it in the estimated time found by machine, you could find a much more definite estimated time, for your process.

authors: ธวัชชัย อัดแสง


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How to generate a STL from a rotational solid of two equations?
I have a solid of revolution defined by two equations, and I want to generate a STL file for printing from the difference of the two equations, revolved around x=0. I can get a good visualization when I query this on Wolfram Alpha, but I cannot figure out how to download an STL of this. I know there is a way to do this via Wolfram's Development Program but I'm not sure how or if that is the best way to do this. Solutions do not have to involve WA.

A programmatic CAD like OpenSCAD or implicitcad will do the job.

Yes, OpenSCAD is free; you should give it a try.

@Davo how can I enter equations into OpenSCAD

Well, I'm not an OpenSCAD guy, but I've seen people work wonders with it. The download includes practice formulas and tutorials, if memory serves.

The best free solution I could find was to graph this (in Desmos), screenshot it, and convert it into a SVG, convert that into an OpenSCAD file, and then use that to make the STL. A similar process is shown on someone's blog here.

The Wolfram Alpha "Data Download" feature supports STL format, but is only enabled with a Pro Account.
When I click your link to Wolfram, I see the visualization of your equations at the bottom of the page; when I hover over the image, several buttons show below it. One of them is "Data", with a download icon. This gives a number of download options. The File Format drop down includes "STL".

I don't have my printing software with me, so I haven't verified that the STL file will be usable...

Is there a way to get this without a pro account? (Or could you share the STL with me?)

I don't have an account at all. I'm not signed in, I just clicked your link. I'll see if I can add screenshots to my answer.

Ah - I see the actual download is disabled without having a Pro account. I will revise my answer.


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Best practices to fix a threaded nut inside a print
I'm trying to connect two 3D printed parts (ABS) together with a threaded connection. Thus, I need to fix a threaded metal nut (M4) inside a corresponding slot which I've implemented in the design.
Right now I apply a conventional super glue on the nut and press it inside the print, wait for a couple of hours and then use it.
Problem is that the nut keeps falling out of the print when I apply a more tension to the bolt. Can you please advise me on how to make this method work. Maybe some of you aware of special glue for that purposes?

One good option would be to - if possible - change the design, so the nut is inserted from the opposite side, so that the bolt just pulls it in tighter rather than pulling it out.
Another option would be to instead of using a nut, use a brass threaded insert. These are like nuts, except they have ridges that are specifically aimed at locking it inside the plastic.

huh! that's smart!! ))

There are a larger variety of threaded inserts - not just brass.  Just note that for maximum hold, make sure that you insert them from the opposite side from where you will insert the screw,  If you are going to press them in then I would recommend the ultrasonic ones.

Instead of super glue, you could try a two part epoxy resin (any brand should do, i.e. Bison Kombi Power or JB Weld). This may take longer to dry, than the super glue, but should be much stronger, and deal with torsion forces better1.
Or, you could try red (not blue) Loctite. However, the epoxy resin would probably be stronger.

1 This is admittedly an opinionated reference, but from Epoxy or super glue, which is stronger?

depending on the surface, [epoxy] can be superior. Epoxies are generally a must if the surfaces are porous

and

Epoxy is superior to CA. CA is nearly always misapplied. Epoxy has a higher tolerance to misapplication thus is much less likely to fail under such circumstances. I've used Belzona epoxies to repair parts on various aircraft and spacecraft where welding would be inappropriate! Belzona epoxy is without a doubt the best there is. Too bad you cannot purchase it in Home Depot.
The closest thing you can get though is PC-7.

Just heat the nut with a soldering iron to seat it into place (after the print). I've done this many times myself.
EDIT: Try a bit of acetone, to allow the ABS near the nut to reflow.

Yeah! I know that trick. I do it before I glue the nut inside. But it goes out anyway :/

Oh. Have you tried a little bit of acetone instead of glue? To melt the ABS?


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Does the Da Vinci line of 3D printers come with a heated bed?
I'm now currently looking at getting my next 3D printer, after my success with the Prusa i3 Reprap Build, and I have had my eyes on the Da Vinci line of printers for some time now.
What I want to know is, does this line of 3D printers include a heated bed? Or does it come with a stock aluminum bed?

Literally the very first google return for "Does the Da Vinci line of 3D Printers come with a heated bed?" is The Pro has adjustable heat settings for the nozzle and the aluminum print bed...

I did do a google search about the Da Vinci Printers and their heated beds. But I wasn't sure if an aluminium bed is the same as a heated bed

Are you sure you want a DaVinci?  They are the best seller on Amazon, but they have chipped filament which you either have to buy theirs or hack around.  Nothing wrong with a razor and blades business model if you like the blades and are willing to pay extra for them, but there are so many options out there that are more DIY friendly and isn't that the 3d printer ethos anyway?

I am sure I want a Da Vinci 3D Printer. I do understand that the DIY kits offer more freedom than pre-built kits. But due to time constraints and requirements, I need a 3D printer that is ready straight out of the box

You can flash several of the models with Repetier firmware allowing you to do whatever and use whatever filament, there are also several workarounds if you want to use your own filament without changing the firmware.  I have a DaVinci 2.0A with both hotends replaced with E3D versions.  I use Repetier on it and I send my prints to it using a wireless SD card.  Repetier firmware can be found here, read all the instructions before doing the flash - https://github.com/luc-github/Repetier-Firmware-0.92

@GipsyD While this is off topic, you may want to take a look at the selection of printers offered by Monoprice.  They offer a comparable level of "Out of the box" readiness at a similar price point, but without the long term commitment to DaVinci filament.  (I strongly considered buying a DaVinci printer before I discovered Monoprice)

Yes. The Da Vinci Duo 2 (most common one) has a heated bed.


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Is it a good idea to include thermal fuses in a DIY 3D printer design?
3D printing should be relatively safe, however, the inherent nature of 3D printers, with all of the heated parts, constitutes a fire risk. A well designed 3D printer should be designed to be as safe as possible, especially one used in the home... Yes, the recommendation is, when printing, to watch the 3D printer at all times and never leave a print unattended. However, with some print times lasting hours and days, this is not always feasible, nor practical. So, some inbuilt safety features should be included, to at least mitigate the risk of fire, to some extent.

Is the use of thermal fuses1,2 a good idea3?
Would you use more than one?
Where should one place a thermal fuse? Next to a particular component, or free standing, in the air, to get an average, rather than highly localised temperature?
Against which components should a thermal fuse be placed? There are a number of places to choose from, such as next to:

The hotend?
The heated bed?
The extruder?
Each of the stepper motors?
The power supply?
The RAMPS stepper motor drivers?

Of lesser import, which type should one use4, radial or axial?

Has anyone added thermal fuses to their 3D printers? Or has anyone examined where the thermal fuses are placed in commercial 3D printer designs, if used at all?

Background
I have recently found myself having to repair rice cookers and fans in Thailand. In those, it is very often the thermal fuse (axial thermal fuses for the rice cookers and the square "radial" types for fans) that requires replacing, as they have blown before the device got hot enough to start a fire. This got me thinking about their use in a 3D printer.

Footnotes
1 We are not talking about the standard, replaceable, thermo-fuse,or fuse, which blow upon a current surge, short-circuit, etc. These are thermal fuses that contain metal connector within them that melts (permanently) at a specific temperature (typically ~135°C), thereby breaking the circuit.
2 Nor am I referring to resettable fuses (AKA PPTC, multifuse, polyfuse or polyswitch)
3 Would a thermal fuse be preferable to thermal cut offs, in the case of fire?
4 The thermal fuses used in rice cookers are the axial type, and in the motors of fans are the radial type.

I've had a thermistor fail on a 24v printer that had a cartridge heater and it got hot enough to burn the kapton tape before I noticed it.  My point here is I don't think watching or working with the current is a good way to go.  Most heaters we use are capable of burning something by just leaving them on with the 5a they get.  Sure you can find the right heater that won't exceed your temperature with full amperage and unlimited time but then the initial heat up will be terrible.

Sorry, I read footnote 1 and missed the "not". Now that we are talking about those that melt I have other comments!  Last time I looked I believe it was hard to find one that could handle hotend temperatures so mounting near the heater is not going to be possible, maybe further up the heat break but then you need to experiment.  Most fires I believe come from the wiring, either at the bed or controller and that would be difficult to catch with a fuse unless it's already on fire. You would be better off using a smoke detector and shutting the power off and maybe a fuse near the hotend.

@tjb1 - Good points about the wiring, hotend and placement of the fuse above the heat-break. When you say shutting the power off, how do you mean to do that? Automatically, via a smoke detector connected to a power switch? Or manually, upon hearing the alarm? Also, I take it that you mean a thermal fuse near the hotend (in your final clause). Would you like to make an answer out of your comment? However, admittedly, Tom's answer seems to cover most of the points, already... although any additional points would be most welcome...

I never looked enough to see if you could get a smoke detector with a relay for power.  I'm sure you could tap into one and hook a relay to the buzzer but now you're relying on your work so that's up to you.  Yes at the end I mention the fuse on the hotend because I think that's the only place it may be useful and it will need to be placed far enough away from the heater that you don't exceed the fuse limit when taking the hotend to 200-300C. They usually have a holding temp much lower than the opening temp as well, one I seen has a holding of 200C but doesn't open until 240C.

Whether you should use a thermal fuse or not depends on what other safety measures you've taken. You can't look at the safety features of a printer in isolation, you need to look at what other measures are in place.
The main fire hazard in printers is unfortunately (still) the fact that some manufacturers use underrated connectors on their boards, and that some users put bare wires in screw terminals or use inadequate torque when tightening terminals. As the wire works itself loose, it starts arcing and burning the connector. A thermal fuse does not help in this situation (unless you place thermal fuses near all of the connectors, which is impractical). Instead:

Properly tighten screw terminals, check them, and consider using proper wire termination (crimp lugs).
Use strain relief on wires. Make sure wires don't rub against anything, and guide them so they do not bend in a tight radius. Since the extruder (or print bed) is constantly moving, those wires are subject to fatigue.
Make sure connectors (especially those for the heated bed) are rated for the current running through them, and solder wires directly to the board if necessary.

Using a regular fuse may protect against wires shorting against each other should their insulation be damaged. Fuses are usually already integrated into the main board.
Most firmwares include some variant of thermal runaway protection, a feature that monitors the heaters and shuts the printer down if it notices something gone wrong. This protects against:

The thermistor coming loose/reading incorrect values/etc...

but not against:

Bugs in the firmware itself
Failure of the MOSFET

Most printers use MOSFETs to switch power to the heating element. Unfortunately, when MOSFETs fail, they usually fail closed (i.e. conducting). This means that, even if the firmware detects something has gone wrong, it won't be able to do anything about it. Solid State Relays (TRIACs) can fail in the same way.
To protect against this, mounting a thermal fuse (or resettable bimetallic switch*) on the heated bed may be a good idea. However, thermal fuses with ratings up to the operating temperature of a hotend do not appear to be available so this is not an option.
Attaching the fuse physically to the part it is monitoring is the most reliable, but for instance with the hotend (if you wanted to protect it all) this might not be feasible to the high temperatures involved so you'd have to settle with monitoring the air temperature close by.
Also consider thermal balancing. A thermal fuse is unnecessary if the component can not overheat to begin with. For instance, most MK2 heated beds struggle getting up to even 100C, so even with a shorted MOSFET they present no danger. However, if you have a powerful high wattage (mains-powered) heated bed, you should definitely install thermal protection.
E3D supplies their hot ends with 25W, 30W and 40W heaters. The 25W heater is the safer choice, since it limits the maximum temperature the hot end can get to, while with the 40W heater you can reach higher temperatures (and reach them faster). Barring a very unlikely scenario in which simultaneously (1) the power supply fails and starts supplying excessive voltage and (2) the MOSFET and/or firmware fails, a heater that is sized appropriately to the load it is driving can never pose any danger.
I don't think it's common to install thermal fuses on steppers, stepper drives or the power supply (which should have its own protection). For every possible location to place a thermal fuse, you can probably think up a failure mode in which that fuse would save the day, but at a certain point it just becomes overkill. The stepper drivers would likely burn out well before the steppers would get hot enough to pose a threat, and overheating of the stepper driver would probably (violently) destroy it but afterwards it should not pose any threat.
Axial v.s. radial does not matter, just use whatever is convenient for your situation.
* Note that some bimetallic switches short one of the leads to the (metal)
 case when tripped, which poses a danger, especially with mains-powered heaters.

Yes, you should use a thermal fuse. But only to protect the board itself from an overheating condition. PTC fuses however; is a no.
The PTC resettable fuse after it trips the first time, doesn't return to it's former low impedence state for a long time. Sometimes hours, sometimes days, sometimes years. As it maintains its higher resistance even though the system is not in an over heated state, the fuse will trip faster the next time. This could lead to false positives during print or other operation.

The resetting will often not take place even if the fault alone has
  been removed with the power still flowing as the operating current may
  be above the holding current of the PPTC. The device may not return to
  its original resistance value; it will most likely stabilize at a
  significantly higher resistance (up to 4 times initial value). It
  could take hours, days, weeks or even years for the device to return
  to a resistance value similar to its original value, if at all.

https://en.wikipedia.org/wiki/Resettable_fuse
Currently, I am investigating the use of a hall effect current sensor and some circuitry. Based on the duration and magnitude of the current, a small capacitor is charged. When a threshold is reached (as determined by a voltage comparitor), the power is withdrawn to let the capacitor discharge (and the heating element cool). This should keep the heating element from reaching a temp above a configurable maximum.

A PPTC, or polyfuse, is not a thermal fuse, although (confusingly) they do operate due to temperature rise due to over current, whereas a thermal fuse operates due to external temperature rises. PPTC do indeed reset themselves (over time), albeit with a different impedance, but they reset themselves nevertheless. Thermal fuses are one-time use which break, open circuit, and need to be replaced. So the line No, you should not use a thermal fuse seems a bit misleading (and possibly dangerous advice). The rest is good though.

Yes, measures which decrease the chance of a fire are a good idea.
In a DIY project, such a fuse is indeed a good idea. I use a printer/software/firmware package which monitors the temperature and fails open (removing current) if readings are out of range; however, there is also hardware protection (a thermal snap switch) just in case the other precautions fail.

IMHO - if you seek hands-off unattended fire safety you'd be looking at something a bit more specific to that job than measuring or limiting the temperature of printer components. That's great, as far as it goes, when it works, but it's not anything like a complete solution. Cutting off the electrical supply won't put out a fire that has progressed to burning plastic, etc. Reasonable over-current protection for a start. Contain the printer inside a metal cabinet or cementboard-lined closet (a non-flammable enclosure), add a heat and/or smoke detector in the top of that enclosure, and rig that to not only cut off power to the printer, but (given things have gone far enough wrong to set that off) also set off an extinguishing means (the effectiveness of which will be enhanced by an enclosure.)
A little bit of looking finds (for predictably high prices, sorry) that there are, indeed, fire extinguishers with a "sprinker-head" valve attached for this type of "spot suppression" job that would cover the "set off an extinguisher" part of the job without need of any power. You'd still want a heat detector that would shut off the electrical supply to the printer in the event of abnormally high temperatures in the enclosure, and you might want a smoke detector doing the same.
This is probably representative of about 0% of actual installations at present, but it would be a good way to reduce the risk in the event of a serious malfunction. Presumably the current distribution of risk looks a lot like the maker stating:

"the recommendation is, when printing, to watch the 3D printer at all
  times and never leave a print unattended."

And then the user choosing not to do so, putting the responsibility for any bad result on the user as not following the maker's recommendation, however impractical.

I have a Thing-O-Matic which included a thermal fuse above the heat break.
For my home-brew printer (a large delta machine) I have a smoke alarm and a fire alarm mounted under the top of the print volume.  These are wired together and give me a NO and NC dry contact.  My plan is to connect this to a power kill circuit.  I haven't found a good way to flood the entire machine, including the electronics, with CO2 gas or another extinguisher when the alarm sounds.
I've added some additional information on parts purchasable on DigiKey:
The first is a 10 A, 152 C thermal fuse rated for line voltage.  This would be appropriate for bonding to a heated bed.
The second is rated to trip at 260 C.
Both of these are less than $1.50 each.

That second part does not trip at 260°C, that's the max reflow temp. It actually trips at 210°C, typ. It's nigh-on impossible to find TCO's from a reputable supplier (i.e. not eBay) with a high-enough trip-temperature for the hot-end.

@SiHa Thanks for double checking.  I'll take another look at the spec.  If there isn't a thermal fuse that can be directly used on the hot end, perhaps it would still be helpful to put a lower-temperature fuse on the cold side of the heat break?

I only checked because it excited me, having spent quite a few hours, a few months ago looking for just such an item :)

I haven't found a good way to flood the entire machine, including the electronics, with CO2 gas or another extinguisher when the alarm sounds.
A servo or some other actuator attached to a fire extinguisher, and then attach it to a thermocouple or some other sensor.  Maybe a knockoff Arduino, which the small ones are 2 bucks a pop.  Since Arduinos are open source, you aren't pirating anything, so clear conscience.

I've heard of folks placing self-activating fire extinguishing balls above their printers. Not sure if those things actually work or not but it would be worth investigating.

I'm going to set this up for my printer: 3D Printer Safety Shutdown - Smoke Detector

Looks like a great solution for preventing fires.

Welcome to 3D Printing SE.  We look forward to many contributions and questions from you.  This would be a better answer if it contained information about what you were linking to.  Links come and go, but we want answers to remain forever.

@cmm - I've updated the answer with some relevant info from link. It might need a bit more though..?


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Plastic most closely mimicking Ultem in Autodesk Inventor
I'm trying to run a stress analysis on an assembly of parts that will be printed in Ultem 9085 (on a Fortus 400MC). I am trying to find a plastic that most closely mimics the material properties of Ultem in the Inventor materials library. SOLIDWORKS had PEI which was near perfect, and I see that there's a thermoplastic resin in that library, but I can't seem to find PEI in Inventor. I was wondering if that thermoplastic resin is the best option, or if anyone knows another material in the Inventory library that would be more applicable. Thanks!

I'm not sure you'll find any. 3D printed parts are non-isotropic due to the layers. I'm pretty sure any simulation will assume the plastic is isotropic.


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My Prusa i3's Z-axis will only go up
If I send it commands to go up, the steppers rotate things up. If I tell the Z-axis to go down, nothing happens. I inverted the Z-axis in the firmware (by setting the value to true instead of false), and it did the same thing, but the other way around - it would only go down.

If the solution provided fixed your problem, then please mark the answer as accepted, otherwise it will remain in the Unanswered Question list and as we are a beta site, in it important to keep this list as small as possible. If it did not then, please, provide more information. Thank you.

It sounds like your Z limit switch is stuck.
The firmware will prevent the motor going further down past the limit to prevent damage.   Be careful going up because if the firmware doesn't know where the bottom is, it doesn't know where the top is.
I checked my printer (an i3 clone) and the limit switches are wired as NC (normally closed).  That means that the circuit opens when the switch is activated.  So, if the wire (or switch) is broken, or if it is unplugged, it will behave as if the switch is activated (the behavior you are seeing).
An easy test would be to switch the x-limit and z-limit cables at the controller board.  If the problem moves to the x-axis, you have found your problem.  BE CAREFUL not to run the motor into the end stop and damage something since there is no limit switch to protect it.


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How to build Cura on Windows?
I am interested in doing development on Cura.  Initially I want to start with the UI rather than the Engine.  I have found the repository and have cloned it to my PC.  I have also looked over the Wiki and searched the web.  For such a popular open-source product, I was surprised I couldn't find a build guide.
Can someone direct me on how to get started.  I have a LOT of experience in Software Development (more years and languages than I want to admit to); but, I have never used Python.  Consider that in your instructions.

This is related, but for Ubuntu How to build CuraEngine?

For a similar saga see https://www.bountysource.com/issues/28750036-can-t-build-32-bit-cura-windows-10-32-bit.

I would LOVE to hear from someone that has actually gotten this to work!  In nearly 50 years of programming, I have never seen such a tangled mess (though I have seen some close).

I found the source code to Slic3r.  The build process appears to be MUCH better documented.  https://github.com/alexrj/Slic3r

The repository's README.md includes a section titled "Build Scripts", with a link to another repository: https://github.com/Ultimaker/cura-build
This includes dependencies and instructions for building Cura on Windows.

WOW, that is a LOT of stuff to install !!!

OK, instructions get a bit dicy when you get to numpi and scipy plugins.  I installed 64-bit Python 3.5 and I have an Intel processor,  I cannot find a match for that for numpy.  Best I could find in cp35m-win32.  When I try that I get unsupported wheel.  Only 64bit they have is amd.  What do I do?  Anyone done this?

Note: The cp35-win_amd64 versions install ... whether they will actually work or not is still a mystery.  Well, the 64-bit version of Cura up on the Ultimaker website had to have been built somehow....

Continuing down the path ...

OK, so it seems that the "cura-build" is intended to do everything in the README.md; but, there are no instructions on how to run it either.  Cura may be a nice application; but, their build instructions and environment is HIDEOUS.  Maybe that is why 8 contributors are responsible for 93% of the commits.  Seems more open source in concept than in reality.

To be honest, I have not even attempted building or contributing to Cura. (I have an interest in OSS, but don't have the time to keep up...) I skimmed the cura-build info, and thought it was complex and unclear as well.

As you are an experienced developer, these links should help:
This is a related question, but for Ubuntu How to build CuraEngine?
Wikipedia has an informative page on Cura, which lists the Github development pages:

Cura Github development page
Cura Github legacy (pre-Ultimaker) development page
Cura slicing engine Github development page

Reading the development pages is a good place to start. The Cura Github development page does contain resources for Windows.
The top level Ultimaker Github page contains links to all of the relevant repositories, amongst other useful resources, including:

CuraEngine - CuraEngine is a powerful, fast and robust engine for processing 3D models into 3D printing instruction for Ultimaker
  and other GCode based 3D printers. It is part of the larger open
  source project called "Cura".
Cura - 3D printer / slicing GUI built on top of the Uranium framework
cura-build - Build scripts for Cura

With respect to Python, I, myself, am slowly making my way through this Python tutorial, Python Code Academy. However, there are a many other good Python tutorials out there, the best resource is probably Python.org.
One thing to note is that Python 2.x and 3.x are markedly different (see Should I use Python 2 or Python 3 for my development activity?). What should I learn as a beginner: Python 2 OR Python 3? is also an interesting read.

Regarding the Python version, the Cura buid ReadMe says Python v3.5

I have been writing computer programs since 1971 and their build environment seems near impossible to figure out.

@markshancock - I feel your pain. With certain projects, I find that instead of trying to fix an issue yourself and submitting the change, in fact, it can be a lot more efficient to just report the bug that you wish to be fixed and just let the developers get around to it, rather than having to wade through the output of someone else's (badly commented) mind. Obviously, if you are looking to fix more that just a few bugs, and make a wholesale change/contribution then that approach is no longer valid... Good luck :-)

Interesting quote from one for the Cura developers discussing building Cura.  "I "jerry-rigged" a setup that lets me run Cura from source, on windows.".  Not very inspiring.  Another quote in the same discussion mentioned that all or the developers at Ultimaker have their own buid environment.  Reminds me of another product where the developer's version control approach was to keep a separate laptop with the last stable build on it.  My goal is to be in a position to be one of the developers (if I chose to be).

Hey,  I know!  Let's get  Linus to take over the project!  :-)


text:
Anet A8 beginning layers not printing correctly
I have had an Anet A8 printer for about two months now and still have not gotten it to print good prints.
At first, it would only print completely solid parts and every time I would try infill from 10-90% the first layer would not stick or it would print really filmy like. As of now, it won't print the first layers for anything well but once it gets up about 10-ish layers it prints perfectly. I have tried a lot of stuff but it seems to be making it worse.
The pictures show my recent attempt at these settings below (Cura's default for normal quality), the print is supposed to be a 10 mm square. I have gone back to the default settings because nothing else was working.

Using blue painter's tape
Layer Height       0.1 mm
In. Layer Height   0.3 mm
WallThicken        0.8 mm
Top/Bottom Thick   0.8 mm
Infill Density     20%
Grid Pattern
Print Temp         210°C
Bed Temp           65°C
Dia                1.75 mm
Flow               100%
Brim (raft is a little better)

Any suggestions?

In the top picture you can also how the top layer has two bubble effects.

With respect to the filament lifting off, and/or not adhering correctly, on the first layer, see Filament lifts from the hot bed while printing... you may need to clean the bed, calibrate the leveling and the nozzle height (see my answer)

My Anet A8 has a concave bed, which is a defect. Check if yours has the same defect by putting a long ruler on its edge on the bed and look for a gap between it and the bed in the middle. If you find a gap then it is concave. The best solution is to put a piece of glass on the bed instead of blue tape, because glass is very flat. It will also help a lot with bed adhesion. I highly recommend this mod.

With respect to the filament lifting off, and/or not adhering correctly, on the first layer, see Filament lifts from the hot bed while printing... in particular, you may need to clean the bed, calibrate the leveling and the nozzle height (see my answer).
The fact that the prints are fine, after 10 or so layers, could be to do with the heat - at the higher layers the print is warm and no warping occurs, but below that, maybe the print bed is acting as a heat sink and making the filament cool too quickly - hence the distortion. Are you using a heated bed? If not, then maybe consider installing one.
Not sure about the bubbles: how do your store your filament? The bubbles could be due to water, which expands as it gets hot, thereby causing the filament to bubble. It is best to store your filament in an air tight container, to prevent it collecting moisture and dust from the air.

Try lowering your Z height a bit more for the first layer if you find yourself having bed adhesion problems. What brand of filament are you using? Did you try using some other brands?

When I first started printing with the anet A8, I also had trash first layers.
I tried (almost) everything:

Leveling the bed maniacally several times (all the screws in the
frame need to be very tight)
Varying bed temperature and nozzle
temperature at all possible combinations.
Adding blue masking tape

Nothing would significantly improve my first layer, except for HAIRSPRAY.
After discovering this secret, I went back and un-varied everything. I tried with and without tape, at high and low temperatures. With-out the hairspray it never stuck well. With the hairspray it stuck perfectly every time. A small spray is sufficient.
After you are done making a mess, use nail polish remover ( acetone ) to properly clean everything.
If you are doubting your G-code, get a pre-generated one for the A8. The ones that came on the SD card should print very well, nothing like the image you showed of the 1st layer.


text:
How do I give 3D-printed parts in ABS a shiny smooth finish?
The surfaces of my printed parts using ABS plastic look rough and uneven.
What methods can I use to achieve a smoother finish for my for 3D-printed objects?

I realise this is something almost everyone is familiar with, but it still needs to be asked.

It is a good question, and one I would like to know the answer to (I am certainly not familiar with it).

Care with acetone. It is toxic.

For PLA, see How do I give 3D-printed parts in PLA a shiny smooth finish?

Acetone can be used to smooth ABS.

The left has been smoothed by an acetone bath and the right is the original model. (Image credit: Andrew Sink)
Take note: acetone is dangerous to breathe in, so work in a well ventilated area. It is also flammable.
Warm acetone vapour bath using stove
This method involves suspending the model in a glass jar of boiling acetone that is heated up by a pot of boiling water.

Attach the model to the lid of the jar with some string, keep the string short, so the model is close to the lid.
Put a few centimetres of water in a pot
Place a rag at the bottom of the pot (to keep the jar stable).
Place the glass jar in the pot, on top of the rag.
Place the pot on the stove and heat to 110°C.
When the acetone is boiling place the dangling model into the jar.
After a few seconds, remove the model.

See here for a step-by-step guide with pictures.
Warm acetone vapour bath using printer bed
This method elevating the model in a glass jar of acetone that is heated up by the printer's heatbed.

Find a non-soluble object that the 3D model can stand on.
Put a teaspoon of acetone in jar.
Place the jar on the heatbed and heat to 110°C.
Place the stand into the jar.
Place the model on the stand, the stand should not let the acetone touch the model.
After a few minutes, remove the model.

See here for an example.

+1 - However... Even though the model on the left looks "nicer" and "more shiny", it should be noted that some of the original detail appears to be lost, (obviously) due to the dissolving process.

This has not worked for me, neither has the rotary rock tumbler


text:
Does anyone know what kind of algorithm Slic3r uses to generate its toolpath?
Is there an algorithm that Slic3r uses to generate the infill? I'm doing a research on toolpath algorithms and improving my prints by the way or controlling the path it takes.
I wasn't too good in searching the right keywords within the source, so it will probably be good if someone could point me to the source code where it works too!

What exactly do you mean by "print its toolpath"? Please be specific about what you want to know, because a description of the entire workings of slic3r would be far too broad for a stackexchange question/answer.


text:
Does anyone know how Slic3r determines its infill adjacent strand spacing, instead of using fill density?
I'm doing research on changing the fill density into the air gap width, adjacent strand spacing, or whatever, instead of using the fill density, as it will give me more precise controls.
Question 1:
All I can work out is from Slic3r's the source code in ~/Slic3r/xs/src/libslic3r/Flow.cpp,
Link to Flow.cpp source code
/* This method returns the centerline spacing between an extrusion using this
   flow and another one using another flow.
   this->spacing(other) shall return the same value as other.spacing(*this) */

float Flow::spacing(const Flow &other) const {
   assert(this->height == other.height);
   assert(this->bridge == other.bridge);

   if (this->bridge) {
      return this->width/2 + other.width/2 + BRIDGE_EXTRA_SPACING; //Line A
   }
   return this->spacing()/2 + other.spacing()/2;                   //Line B
}

If I am right, will changing Line A or Line B, be the right way to change its infill adjacent strand spacing?
Question 2:
And since we're on this topic, what does the bridge variable represent?

This answer should have been a comment, except I have included the relevant code.
To answer question 2, at a guess, bridge is simply a boolean (bool) that specifies whether there is a bridge or not.
From Flow.hpp line 32
/// Represents material flow; provides methods to predict material spacing.
class Flow
{
    public:
    float width, height, nozzle_diameter;
    bool bridge;

    Flow(float _w, float _h, float _nd, bool _bridge = false)
        : width(_w), height(_h), nozzle_diameter(_nd), bridge(_bridge) {};

Additionally lines 68-73, may also be of interest:
    private:
    static float _bridge_width(float nozzle_diameter, float bridge_flow_ratio);
    /// Calculate a relatively sane extrusion width, based on height and nozzle diameter.
    /// Algorithm used does not play nice with layer heights < 0.1mm.
    static float _auto_width(FlowRole role, float nozzle_diameter, float height);
    static float _width_from_spacing(float spacing, float nozzle_diameter, float height, bool bridge);

However, your best bet, to get an accurate answer to both of your questions, is to contact Alessandro Ranellucci - alexrj, and ask him - as he is is the designer of the Slic3r code. When you get a reply, maybe you would like to post the answer here... it may be useful for someone else.


text:
I need an acetone substitute
Acetone is banned in my country, and I cannot get it.
What substitute could I use?

To do what with? It depends what you needed the acetone for? To dissolve ABS? Google lists a number of alternatives.

The answer really depends on what you are using it for. Is it for dissolving ABS? A quick google search should show you what you want.
The thread, Could you recommend me a suitable alternative to acetone as solvent?, has a good many points that are worth considering:
For example, you may need to consider the Polarity Index

Burdick & Jackson solvents are arranged in order of increasing
  polarity index, a relative measure of the degree of interaction of the
  solvent with various polar test solutes.

If you are using it to dissolve a polymer other than ABS, then the family/class of polymer may need to be considered:

Apart from your desired solvent qualities (non-flammability and low boiling point), the choice will be totally dependent on the family/ class which the polymer  belongs. Based on the principal that 'like dissolves like, the attached document will provide you with good ideas on which solvent to use when a particular repeating unit of the polymer is involved.

Butanone is a possibility:

One alternative is butanone (button-2-one) - this is similar to acetone, but has a much higher boiling point. It is often used for alkylations etc. It has a boiling point of 79-80°C compared to 56°C of acetone.

or NMP:

N-methyl-2-pyrrolidone (NMP) can be used. It is a polar aprotic solvent and dissolves many polymers. It has high boiling point ( >200 degree centigrade)  It is soluble in water and easy to dispose which is a great advantage during work up of reactions.

However, some other alternative chemicals are listed here (from Any good alternative to Acetone?:

Butyl alcohol
methyl isobutyl keytone (MIBK)
denatured alcohol
MEK (methyl,ethyl,ketone), i.e. Kleen-Strip MEK Alternative
Ethyl Acetate

Some branded items, from Alternatives to Acetone:

Surfasolve

Surfasolve is a 100 percent biodegradable acetone replacement that removes adhesives, degreases tools and works as a resin solvent.
    Surfasolve is a non-regulated product.

Bio-Solv

Bio-Solv is an acetone replacement that is 100 percent biodegradable. It is not deemed a hazmat, so shipping will not cost
    you more. This acetone alternative is not listed on California
    Proposition 65, a law passed in 1986 to keep substances that cause
    cancer and birth defects out of drinking water. Nevertheless, you want
    to use Bio-Solv in a well-ventilated area because of an unpleasant
    odor. It is not, however, a hazardous air pollutant. Bio-Solv is not
    petroleum based.

Replacetone

Replacetone is another acetone alternative. It is nonflammable and nonvolatile. It can be used as an acetone or MEK (methyl ethyl ketone,
    an industrial solvent) replacement that is biodegradable. Both
    Replacetone and Bio-Solv are referred to as green acetone.

Methyl Acetate

Methyl acetate is offered as an acetone replacement. Manufactured by the Eastman Chemical Company, it is utilized in industrial
    applications. It is biodegradable, volatile organic compound exempt
    and non-HAP (hazardous air pollutant)

Important note
However, some of these items may also be banned in your country, so check first. As you do not say which country that you are from, it is not possible to qualify this statement.
It is worth remembering that some of these substances are not as safe as acetone, and the fumes may be more toxic, so they should always be used in well ventilated spaces.

Just an aside, butane and methylethylketone (MEK) are the same molecule. If acetone (dimethylketone) is outlawed, then I would guess that MEK is also illegal.

I have used DCM (dichloromethane, or ethylene dichloride) to dissolve ABS (or cold-weld/glue parts together).
From ABS wikipedia page:

ABS polymers are resistant to aqueous acids, alkalis, concentrated
  hydrochloric and phosphoric acids, alcohols and animal, vegetable and
  mineral oils, but they are swollen by glacial acetic acid, carbon
  tetrachloride and aromatic hydrocarbons and are attacked by
  concentrated sulfuric and nitric acids. They are soluble in esters,
  ketones, ethylene dichloride and acetone.


text:
Best method to make dissolvable supports?
Sometimes supports are very difficult to remove (physically) when I print with ABS. The image below, from Thingiverse - MOF-5 unit cell, is after significant effort to remove the yellow ABS supports from a black ABS model.

I've learned about polyvinylalcohol (PVA) as a 3D-printing filament which is soluble in water. It seems like a great option for dual-extruder printers, where you can print the model with ABS or PLA and the supports with PVA, then throw the whole thing in water and let the supports dissolve.
I've considered other options since PVA is ~4x more expensive than ABS.
Doing a PLA print with ABS supports, followed by dissolution of ABS with acetone, is my best idea currently.
Has anyone found success with another option?

PLA is not completely immune to acetone. It's unlikely you'll have any success trying to dissolve ABS supports away from a PLA model.

PLA supports come off a lot easier than ABS supports.    Have you tried printing the object with just PLA?

Don't bother with ABS supports for PLA models… the two don't adhere well, and the acetone bath will bleach the PLA as well as staining it with whatever pigment is in your ABS support. I tried a few times and it never ended satisfactorily. See my answer below for a recommendation/alternative to PVA.

@khaverim Have you fixed this issue? i'm seeing that your supports are too heavy, try to use a less population like 50% or 40% of the infill support, also separation will help to avoid to get adhesio to the walls.

I've had great success printing with HIPS (high-impact polystyrene) as a support for both PLA and ABS. Most sites recommend it for use with ABS because the materials melt at similar temperatures and work best with heated beds, but I've had good luck using it as a support material with PLA on a bed at 60°C. It doesn't stick as well to PLA as it does to ABS, so supports tend to peel away very readily. The downside is that, if you need the support to anchor your print at all, it doesn’t really stick well enough to accomplish this task. For that, you must pair HIPS with ABS.
When you print with ABS or have complicated interwoven support structures, HIPS can be dissolved with D-limonene, a citrus based cleaner sold under various names like Citrisolv (others exist), or with dipentene (a mixture of L and D-limonene that doesn't smell as pleasant).
Regarding cost: I've found HIPS to be slightly more expensive than PLA/ABS, but only 1.5x the cost, not 4x like PVA. Additionally, it isn't hydroscopic in the same way as PVA so it lasts longer out of the package. Since you're using it as support, you also tend to use far less filament than you do for the main print (sparse support structures as opposed to solid print structures).
Water-soluble alternatives: There are a few proprietary blends of polymers sold by the big commercial printer manufacturers (3DSystems, Stratasys) that only work in their machines… these are generally soluble in basic solutions (water + sodium hydroxide or sodium carbonate). These are usually very expensive and you'd have to rewind the filament on a spool, as they come in cartridges made for specific printers. You'd also have to experiment with the right build conditions and solution blends to remove the material afterward. Airwolf has a support material called Hydrofill that purports to be soluble in plain water… I'm not sure how this is different from standard PVA, though I assume it is different. Hopefully more companies will work on developing water-soluble options to help us keep the 3D printing world full of renewable, less-environmentally-harmful options for filaments (both print and support).
Update:
Ultimaker now has a material called Ultimaker Breakaway. After using it for a few models, it works remarkably well, allowing me, for the first time, to print nice rounded surfaces on the bases of my prints. It really does just break away from the surface, much like HIPS but without the lack of adhesion problems between HIPS and PLA.

I haven't tried this myself, but the recommended way I've seen for dealing with the high cost of PVA is to print the support structure in ABS, PLA, or something else cheap, and print only the interface area (the top of the support where it meets the model) in PVA.

I believe this is on-topic because it describes my experience using PVA in a Prusa i3m3-MMU2 machine.
My experience has not been good.  I started with a new spool, and dried it between attempts.
The problems may be specific to the Prusa MMU2 printing process, but some are intrinsic in PVA, or at least the PVA filament I've been trying, PrimaSelect PVA+ (link is for reference only.  I have no skin in this game.)  Aspects that may carry forward to non-MMU2 machines include:

filament is very stringy,
filament is friable, and crumbles into the drive gear,
filament does not adhere to a PEI bed.  I had to use Aqua Net hair spray.
filament does not stick well to itself.  Stacks of support will have internal defects, which may affect the desired print.
filament is very hygroscopic. With the MANY manual interventions needed with the MMU2, it may help to bake the filament in the middle of a multi-day print.

Perhaps unique to the Prusa i3m3-MMU2 machine, these lead to some specific problems:

the filament may be smaller diameter than 1.75, and it is sometimes
not detected by the filament-presence detectors.  This not only leads to failures, but it may also lead to large blobs of filament extruded into the purge towers, which leads to "crashes" and compounds the next problem.  This may also be because I have too much tension between the drive gears -- something to check.
the purge towers are weak where layers of the PVA overlay each other.  Purge towers may break during printing, which ruins the print.
the MMU2 filament drive gears are frequently fouled by PVA filament bits.  I haven't found, though, that cleaning them reduces feed problems.
the MMU2 system feeds filament through PTFE tubing.  Over time, perhaps with humidity, the friction of the filament passing through the tubes increases, which makes the feed problems worse.

This is not a negative review of the filament itself, or of the Prusa i3m3-MMU2.  I may be doing something wrong, and would love to know better.  I am quite happy with the MMU2, and have tuned it so that it works very well with PLA filament.  This is the result of launching into soluble support, which is a feature I strongly hope to use reliably.
I am still exploring alternatives.

I'm using 3DMaker PVA, and I am seeing some, not all, of the problems you have with PrimaSelect PVA+. The 3DMaker PVA is pretty stringy too, but it is also very sticky, adheres well to itself as well as the build surface (I have a powder-coated PEI steel sheet on my MK3S+MMU2S). It isn't too hydroscopic -- it takes about 8-12 hours to dissolve in still water. The filament is also flexible and doesn't get ground up by the Bondtech gears -- you may have too much idler screw tension. I have also replaced all my tubes with 3mm inner diameter to reduce friction and reduce the chance of grinding.

I will add that I don't see how PVA could be paired well with ABS, which is what the OP was writing about. My PVA has a max temperature of 230C, while ABS typically prints above 250C, I would think you'd get a lot of cooked PVA fouling the nozzle during filament switching. Has anyone tried this?

Not sure if frame challenge is on-topic here, but have you tried using different support options in your slicer? In Cura, I've found the experimental support tree mode both reduces the material usage a lot and gives supports that are easier to remove, at least for geometric (vs "organic", where it's sometimes good and sometimes bad) models. Turning off walls for normal (non-tree) support (infill and roofing only) and/or using a thinner line width than your nozzle can also help with removal but whether it provides sufficient support depends a lot on your model's geometry.

While I haven't used PVA yet, think of it this way, it may be 4x the cost but you use significantly less material for support structures even if you have a lot of support.

As this stands, it does not provide an answer to the question "How to make the supports best". Please extend on what you want to say. Mind, this is not a forum.

Hi Brian, and welcome to SE.3D Printing! :-) Thank you for editing and fixing the missing word in your answer. As Trish states, Stack Exchange is a quality Q&A site and not a forum. Please take a look at the tour and How to write a good answer. Good answers are based on sound experience and in-depth research. If you could expand upon your answer, with more details, examples, etc. then that would be great. Take a lot at other highly voted answers to get an idea of the usual standard. Thx :-)

@brianh Normally the infill support are 60% less than the infill part, however this percertage is strong, but an infill support of 40% or less can help a lot and easy removable, but only we will save the 60% of that 400%.


text:
Printer goes beyond the bed when auto leveling
I am trying to add auto bed leveling to my Prusa i3. When I run G28 my printer hits the X and Y end stops properly, then it assumes X=25, Y=99 position on the bed and performs Z homing, after which it stays there. The problem is when I run G29 then it starts following the grid points from this position and tries to go out of bed.
My settings for the grid are:
#define LEFT_PROBE_BED_POSITION 10
#define RIGHT_PROBE_BED_POSITION 140
#define BACK_PROBE_BED_POSITION 140
#define FRONT_PROBE_BED_POSITION 20

And travel limits are set to this:
#define X_MAX_POS 150
#define X_MIN_POS 0
#define Y_MAX_POS 150
#define Y_MIN_POS 0
#define Z_MAX_POS 220
#define Z_MIN_POS 0

I guess this might be relevant too:
#ifdef Z_SAFE_HOMING

  #define Z_SAFE_HOMING_X_POINT (X_MAX_LENGTH/2)
  #define Z_SAFE_HOMING_Y_POINT (Y_MAX_LENGTH/2)

#endif

What should be added to your question is the offset position of the sensor to determine the correct sensor bounds (see e.g. How to set Z-probe boundary limits in firmware when using automatic bed leveling?). Note that the presented code is somewhat dated w.r.t. current Marlin configuration, but, if correctly inserted, the printer homes in the middle of the bed dimensions.

I don't know how your firmware load handles G29 ,but here's a guess, based on information at the  reprap wiki .  Try using FBLR to force the travel limits.

Parameters
P Set the size of the grid that will be probed (P x P
  points). Not supported by non-linear delta printer bed leveling.
  Example: G29 P4 S Set the XY travel speed between probe points (in
  units/min)
  D Dry-Run mode. Just evaluate the bed Topology - Don't
  apply or clean the rotation Matrix. Useful to check the topology after
  a first run of G29.
  V Set the verbose level (0-4). Example: G29 V3
  T
  Generate a Bed Topology Report. Example: G29 P5 T for a detailed
  report. This is useful for manual bed leveling and finding flaws in
  the bed (to assist with part placement). Not supported by non-linear
  delta printer bed leveling.
  F Set the Front limit of the probing grid
  B Set the Back limit of the probing grid.
     L Set the Left limit of the
  probing grid
  R Set the Right limit of the probing grid


text:
BQ Ciclop or Horus bury the lower part of a model
After all calibrations the models are missing the lower about 10-15mm depending on their size and shape regardless of the value of Pattern Settings/Origin Distance in Horus which happens to be 21.5mm. Tried from 10 to 30mm with no changes in scanned point clouds. What am I doing wrong?
Here's the original:

And here's the scanned cloud:

Although the mission statement for this forum includes tools for 3d printing, this question appears to be quite some distance outside that scope, as it appears to be fully directed toward a scanning application and related problems.

@fred_dot_u - While I would agree, as there isn't currently a specific SE site for scanning, what other option does the OP have for posting their question, except here? Also, I guess, the scanning process does form part of the overall 3D printing process, even though it is more to do with preparation rather than printing per se. :-)

I agree that 3D scanning questions should be allowed.  Scanning is often associated with 3D printing and making this site narrower will make it even more difficult to exit Beta.


text:
Best practise of re-modeling a building
The organization I am working for plans to pull down and rebuild our office building. As some people are a bit sentimental about the old building, we think about making a 3D model of the old building.
The old house was built in the 60s or 70s, when everything was done by hand. So we have some really detailed hand-drawn plans of the building. We also have a nice and detailed (physical) 3D model of the house. However, what we don't have yet is any material that can be processed in modern 3D modeling software.
So this is what my question is about:
What is the best (easiest, with reasonable degree of details) way to make a 3D model of the old building?
At the moment I think of two different paths:

Transferring the hand drawn plans to a 3D modeling software. I think, Sketchup might be suitable, but I am open for suggestions. It should be something easy to start with as I would like to motivate some colleagues to join the project.
Using some kind of photogrammetry software to transfer the (hand crafted) 3D model of the building to an "electronic" 3D model. I have no experience with this method, however if it works it might be much easier to do.

Can you help me to decide which path to choose and give me some tips on how to do it exactly?

Is this question about 3D printing, or just 3D modelling software?  That is to say, do you want to, eventually, print the 3D model, or do you simply want an "electronic" model of your building and just leave it at that? If the latter, then SE Blender may be a better place for your question.

Thank you for your reply. As a matter of fact we do want to print the model once it is done. But also other use cases are possible (like a Bubblegram). I don't think that Blender is a suitable software solution for this problem. Do you?

That are certainly trade-offs between the two options.
I think main trade-off between the two options you described would be visual details vs. configurability.
With a scanned design you have the ability to capture all the visual details that are in your hand crafted model.  Those same details might require more effort than you are willing to put into a CAD design (like window and door detail and other architectural accents).
The big disadvantage of a scanned model it that it would not be parametric so you can't fiddle with design details - like adjusting the width or spacing of the windows, the position of a door or external approach (stairs, etc).  Also you could play with the external skins/finishes and play with how wood looked as compared to concrete of brick.
Another advantage of a CAD model would be that you would not be able to break out components and print them separately because of print volume issues or to be able to print in different colors.
My personal preference would be to create a 3D Model using a CAD package.  The limitation on this would be that it might not have the same level of detail; but it would be much more flexible.  You could probably create the base design pretty easily either from the architectural drawings or by deconstructing the hand crafted model.  The model was probably built from pieces much the same way a 3D CAD model is created.
Here is a good example of how to do that.  In the example, they create a pretty detailed house design in Sketchup in 35 min by starting with scans of the architectural drawings.

There are quite a few other similar videos so you should look for the one that fits you best.

That's a great answer! It astonishes me as I would have seen some characteristics exactly the other way around (I think I would be too lazy to put a skin on a CAD model at all). Still, your argumentation has no flaws. Only problem: Now I want to do both :)

Thanks @speendo, you could probably incorporate both into your design.  Another option I have done is to take photos of some features that would be difficult to create in CAD and then use those as a skin/texture for that piece very similar to how the above roof looks like it has shingles.  That obviously would not 3D print; but, it looks great on the render.

of course! I just wanted to encourage other people to post their opinion :)