text:
Slic3er throws "AMF parsing requires XML::SAX"
When I try to open prepared .amf plate with some items to print, Prusa's Slic3er release throw's this error:

The slicer version is 1.30 distributed for Prusa's i3 MK2 1.75 printer.

Did you end up finding a solution on this? I assume you've tried reinstalling and/or updating Slic3r already, right? +1 for having to mention XML onto this list, which I never expected....

The slic3r software is written in Perl, a programming language that can be expanded with local libraries.  XML::SAX is one such library.  CPAN is a tool which can be used to retrieve libraries from the CPAN repository (Comprehensive Perl Archive Network, I believe).
I use CPAN is something I do infrequently, so I would be doing a disservice by trying to list the steps here.  Better answers are, no doubt, on stackexchange.  Nevertheless, these may help:
From your command line, start Perl running the CPAN module, and invoke the CPAN shell (your input in bold):
> perl -MCPAN -e shell
cpan> install XML::SAX
cpan> ... several lines of output ...
Done!
XML::SAX is up to date (0.99).
cpan> quit
>
With that done, try using slic3r again.


text:
What causes gaps in small region fills and how to prevent them?
I saw this cool Nuka-Cola bottle opener. I made it:

As you can see, nasty gaps have appeared in the text. What could've caused them? I am sure I set the filament diameter correctly. So why did the Slic3er not generate enough paths here to fill the letters properly?
I used Slic3er and Repetier Host. My printer is Prusa i3 MK2 1.75mm. The material I used was PLA.

I had a similar issue as described in this question. Curiously, yours is almost opposite as my raised lettering was OK, but the surrounding areas were poorly filled.
I came to the conclusion that Slic3r was simply not able to properly handle the geometry in my part. I tried with Cura and had great results!

I will sure try it with other slicers. But I was wondering if the Slic3er has a setting that influences this.

If you look closely at the slicer output, you will probably see that these regions just have outer shells, and no infill. What is happening here is that the part thickness is between 2 and 3 nozzle widths (or possibly between 4 and 5). If you ask for a 1 mm thickness, but only have a 0.4 mm nozzle, it is not easy for the slicer to split this into 2.5 passes.
One thing I found would sometimes help is to change the nozzle width setting in the slicer (to maybe 0.39 mm) and this sometimes helps (at the expense of needing to offset the extrusion rate to compensate).
Here are some rectangles of width 0.3 mm to 1.2 mm (increments of 0.1 mm) sliced in Cura 2.31. The first is 'normal', with wall count set to 2. Next is an inaccurate (small) nozzle setting of 0.38 mm, and finally the correct 0.4 mm nozzle, wall thickness of 1. The last setting shows infill (in yellow) rather than an inner wall (green).

Normal has a gap in anything over 0.8 mm wide.

If I reduce the nozzle width, I do get some inner walls, but only where there was already space for 2 walls.

When I only request one wall, the rest infill, (even though I have 20% infill), then the result is as expected. This seems to be a bug in Cura (or at least something which is improved in the version currently in beta).
There is a bit more detail in this question Missing top layers in Cura

The proper term here is Under Extrusion.
There are a lot of reasons this can happen. For my Ultimaker, over time it developed very bad underextrusion due to the build up of carbon. I had to do atomic pulls / increase the extrusion multiplier.
I would ...

verify that you move exactly the amount of plastic you think you are. Mark 200mm of material. Extrude 100. Fix the firmware steps per mm for Extruder if incorrect.
triple check the filament measurements. Try all along the length. See if the plastic has bad variance.
Verify that it is not printing as expected. Is your slicer generating the gaps? Letters are hard for slicing programs. If it cannot print a full line, it often will print a gap. You can adjust this by allowing greater line overlaps. This is probably what is happening.

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text:
Turning off heatbed for the last few layers. Good idea or not?
My heatbed won't let go off the prints until it considerably cools down. The cooling process takes decent amount of time.
I was considering putting the M140 S0 (sets heatbed temp to 0) somewhere near the end of the printing process, so that when the printing is done the cooling is already in process.
Is that a bad idea? I am asking because if it was 100% perfect idea, slicer would probably do it already.

About: "if it was 100% perfect idea, slicer would probably do it already". No; this is a bad assumption! Today's slicers are great, but they are very far from perfect or feature complete. Please keep having clever ideas and don't let current slicer capabilities limit your thinking. =)

Some months later, did you experiment with this? I have the same problem, to much work so no time enough to let the prints cool.

It's not a bad idea, and you should try it. But only on prints with some height, because:
The goal of the heated bed is to ensure adhesion for the first few layers. Without the heat on the bottom side of the layer, the layers above will pull those layers with it as they cool, causing the warp that you see. When your bed is warmer than the layers above, those first layers stay with the warmth. This continues as the layers above are pulled into adhering to the bottom layer instead of going rogue.
Print some objects that are taller than 10 layers, and see. When you succeed, get scientific and dial down the amount of layers until you see warp. Then you'll know which object height you can employ this.

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text:
PLA bubbling in the first layer of a print
I am using a Prusa i3 printer and just recently I have been having problems with the first layer. Here is a picture of what it looks like.

I have tried levelling the bed and it seems to be level. I was using a glue stick before but it started bubbling on that, so I switched to tape and that worked once but it is not working now. I wiped the tape with rubbing alcohol and it happened again.
What else can I do to get the first layer right?

Could you provide the following values of your print: nozzle temperature, bed temperature, nozzle diameter, first layer height

Oh wow. You are way over cooking your PLA. It is bubbling because it is BOILING. I can tell you have it too hot because the lines are all blurred as if they are liquid and pooled together.
That said I can't give you details because you didn't post settings. I would start by turning the temps to 170 °C for hotend and 60 °C for plate. Also the gluestick it self should never bubble. It is unclear if that is an issue..

Either you are extruding way too hot, or your filament has absorbed too much moisture and the water absorbed inside the filament boils instantly in the extruder, resulting in a gap or "bubble" in the filament, leading to bad extrusion. What temperature are you extruding at with your PLA? Hope this helped!

If it is a water issue then their print will make crackling snap noises.

I had this problem and I had to adjust the nozzle temperature 10 °C below the minimum temperature of 190 °C!

Hi and welcome to 3D Printing.SE! Your answer is marked as a low quality answer by the community, as it is now it is more a comment on the question. Please expand the answer, e.g. explain what is the minimum temperature? Is this the minimum value that is recommended by the manufacturer?


text:
Easy way to create honey comb filling for a generic printer/onshape
This is my second 3D model, be forgiving... ;)
I have constructed a 3D model with some bigger solid parts with FreeCAD. After uploading it to shapeways, it turned out to be too expensive to be printed like that.
Googling around, gave me the solution to make it hollow and use a support structure. If you know which exact printer model is doing the print, Slic3r can do the job. But as I want to print with shapeways, I just know the material, and they are doing the slicing. Obviously without creating support structures in solid parts. Hence, this way does not work in my situation.
Searching for an other solution, I found this article, FreeCAD: Perforated Sheets and HoneyComb, describing how to create a honeycomb structure by a little piece of code. I would have to make my part hollow by subtracting a shrunk version of the model and fill it with the honeycomb structure. This sounds feasible to me, but is quiet a certain effort.
Is there an smarter solution to achieve a hollow piece with support structure?

If they do the slicing then they will sure generate honeycomb (or other) filling anyway. I actually believe generating your own filling like this could mess up the print. Don't they have a setting or option for fillings in the order form?

@TomášZato I don't think, they do a filling optimization. Otherwise, I could not believe the high price for the small model. It is about 6x6x2,5 cm, has to big cutouts and should cost nearly 50€.

If you want to have a specific infill density, you can design the infill yourself as part of the solid model. (Note I use these two methods to design parts for strength, but it's basically the same thing that you're looking at doing)
I have two methods for doing this as follows (I use Solidworks, but the features exist with most CAD software)
Method 1
Step 1
Design the part for the geometry that you'd like as you usually would. (check the volume of the part)
Step 2
Hollow out your part and set your wall thickness to the desired dimension. In solidworks, you can use the shell command for this. (check the new volume of your part)
Step 3
Create a pattern for the print orientation  you want and make the thickness of the pattern set to a variable you can easily change. For example if you want a hex pattern, then create a hex pattern that covers the footprint of your part.
Step 4
Extrude your pattern from the bottom surface to the upper surface.
(depending on how complex your part is you may have to iterate between steps 3 and 4 to fill the part completely, but that's half the fun).
Step 5
Close the part off. The Shell feature hollows out a part, and removes most of one flat surface. You just need to go back in and close this surface off again once you're done, generally with a single extrude.(check the volume of your part again)
Step 6
Now you can compare the volumes of your part, this may require you to change the thickness of the hex pattern, and may require several iterations to get an exact density that you want.
This process wont necessarily work for every part you come up with but it's a good start for fairly blocky parts. It's also relatively quick and easy to do.
The second way is as follows
Method 2
Step 1:
Create your part as usual and save as a unique file (lets call it "Solid file")
Step 2:
Create hollow the part out and save as a unique file (lets call it "shell file")
Step 3:
Create a new part that is your hex pattern, but instead of modelling the walls that will be in your final part, create the hex voids as a solid. Save this as a separate unique file ( lets call it "Void profile")
Step 4:
Create a new part and import both the "Void Profile" and the "Solid File".
Step 5
Subtract the "Void Profile" from the "Solid File"
Step 6
Import the "Shell file" and merge it with the result of step 5
This process I like a bit more, but it takes longer, creates more files and is a bit messier I think. However it gives you a lot more control over how your voids will work and you can delete sections of the voids if you want different parts to be more solid that others.
If you're using solidworks shell model and you have very tight features sometimes it gives you errors, and you may need to suppress small features and then add them back in after all of this. Just a heads up, it can be a bit of a flaky feature to use sometimes.
Now that you have your 'designed' internal structure don't forget to print at 100% infill, otherwise a slicer program may hollow out your designed infill pattern.


text:
What kind of colors should I use to paint my PLA prints?
I'd like to paint my prints, which I printed using white PLA, with some colors. I have no idea what type of paint should stick to PLA well. I need paint that will not be soluble in water and will stick good enough.
What kinds of paints do people use to paint PLA prints?

Fortunately, PLA accepts many types of paints, most common of them is acrylic paint.
Acrylic is water-soluble until it dries, then it becomes water-resistant.
Depending on the goal you plan to achieve, different types of paints can be used - oil paint, already mentioned acrylic, enamels or lacquers.
Keeping in mind that manufacturers may present different types of plastic under the same 'PLA' brand, it is always good idea to try selected type of paint on a print sample to ensure that it sticks well enough and not melts the print too much at the same time.

Agreed those should all be fine for PLA. However, some other plastics (like polycarbonate) don't play well with some solvent-based paints (like enamels). It never hurts try a sample with a new plastic+paint combination.

authors: გოგა გიორგი ღლონტი


text:
Where to find Z coordinate in G-code for Delta printer
I´m currently writing my own firmware for a custom Delta printer. Therefore I also need to read G-code from programs like Slic3r. Even with a small example like a cube, I´m struggling to find out where the Z-coordinate is hidden in the code. Here is a small example of the code.
; generated by Slic3r 1.2.9 on 2017-02-13 at 15:08:01

; external perimeters extrusion width = 0.50mm
; perimeters extrusion width = 0.58mm
; infill extrusion width = 0.58mm
; solid infill extrusion width = 0.58mm
; top infill extrusion width = 0.58mm

M107
M104 S205 ; set temperature
G28 ; home all axes
G1 Z5 F5000 ; lift nozzle

M109 S205 ; wait for temperature to be reached
G21 ; set units to millimeters
G90 ; use absolute coordinates
M82 ; use absolute distances for extrusion
G92 E0
G1 Z0.500 F7800.000
G1 E-2.00000 F2400.00000
G92 E0
G1 X-31.893 Y0.000 F7800.000
G1 E2.00000 F2400.00000
G1 X-31.893 Y-25.001 E3.57871 F1800.000
G1 X-31.496 Y-27.307 E3.72646
G1 X-30.350 Y-29.347 E3.87420
G1 X-28.588 Y-30.886 E4.02194
G1 X-26.413 Y-31.748 E4.16968
G1 X-25.000 Y-31.894 E4.25936
G1 X25.000 Y-31.894 E7.41663
G1 X27.306 Y-31.497 E7.56437
G1 X29.346 Y-30.351 E7.71211 F1800.000
G1 X30.885 Y-28.589 E7.85985
G1 X31.746 Y-26.414 E8.00759
G1 X31.893 Y-25.001 E8.09727
G1 X31.893 Y25.001 E11.25470
G1 X31.496 Y27.307 E11.40244
G1 X30.350 Y29.347 E11.55019
G1 X28.588 Y30.886 E11.69793
G1 X26.413 Y31.748 E11.84567
G1 X25.000 Y31.894 E11.93535
G1 X-25.000 Y31.894 E15.09262
G1 X-27.306 Y31.497 E15.24036
G1 X-29.346 Y30.351 E15.38810
G1 X-30.885 Y28.589 E15.53584
G1 X-31.746 Y26.414 E15.68358
G1 X-31.893 Y25.001 E15.77326
G1 X-31.893 Y0.075 E17.34724
G1 E15.34724 F2400.00000
G92 E0
G1 X-22.715 Y-22.716 F7800.000
G1 E2.00000 F2400.00000
G1 X22.715 Y-22.716 E4.86865 F1800.000
G1 X22.715 Y22.716 E7.73745
G1 X-22.715 Y22.716 E10.60609
G1 X-22.715 Y-22.641 E13.47016
G1 X-23.607 Y-23.609 F7800.000
G1 X23.607 Y-23.609 E16.45155 F1800.000
G1 X23.607 Y23.608 E19.43309
G1 X-23.607 Y23.608 E22.41447
G1 X-23.607 Y-23.534 E25.39128
G1 X-24.500 Y-24.501 F7800.000
G1 X24.500 Y-24.501 E28.48541 F1800.000
G1 X24.500 Y24.501 E31.57969
G1 X-24.500 Y24.501 E34.67382
G1 X-24.500 Y-24.426 E37.76336

Here are some configuration details:

G-code flavor: RepRap

Nozzle diameter: 0,5 mm

Filament diameter: 3 mm

Layer height: 0,4 mm

Perimeters: 3

Solid layers top: 3

Solid layers bottom: 3

I will also provide the full G-code.

It isn't hidden at all. It's just that the Z-axis position only changes with each layer change, so the Z coordinate is only passed at layer change. On line 19 of your example G-code, it starts the first layer at Z=0.5mm:
G1 Z0.500 F7800.000

The next time you should expect Z to appear is on the next layer.

Your included code has a line which reads:
G1 Z0.500

I checked a couple of my G-code files for some of the past prints and I was able to identify the bed movement relative to the layer being printed. My slicer (Simplify3D) provides for the bed to drop during certain movements. I found G1 Z0.600 followed by G1 Z0.850 for one of the layers. When that layer was finished the 0.600 changed to 0.900 and the 0.850 changed to 1.150.
This fit in with the model's layer height of 0.300 mm for that job.
I did not find more G1 Zx.xxx codes in your sample, but a larger file would contain those lines.

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text:
Marlin: possible to set ZMin limit when ZProbing?
Question: Can a "ZMin-while-probing" be set?
Meaning a minimum Z height the printer bed can move to, while Z Probing.
Purpose: For safety reasons should the probe switch not fire for some reason.
--
in Marlin Configuration.h, I see you can set the height of the Z Axis before deploying the ZProbe:
#define Z_PROBE_DEPLOY_HEIGHT 35
In the context of this question, this is effectively a "ZMax-while-probing", i.e the lowest possible the print bed will be before Z Probing commences.
I am looking for a "ZMin-while-probing" equivalent.  The reason for this is just an added safety check - I know that if the probe switch doesn't fire by Z<=25, then it is not going to, and with this particular printer configuration, that would result in the Z Probe being driven into the printer bed.
Does a setting already exist to create a sanity-check here?

You have not stated the version of Marlin you are using. I will assume we are discussing the latest Marlin 1.1 RC8.
There is no longer any Z_PROBE_DEPLOY_HEIGHT but in earlier Marlin versions it did not function as you think; it was used to signify the amount of Z travel to execute prior to Z probe deployement. This is to ensure available space for servo-mounted, sled, or other types of "stowed" probes.  This was not a limit to the Z travel, but the amount of Z travel to always execute before begining homing.  If a printer without Z_MAX_ENDSTOP is left at maximum travel position, using non-zero Z_PROBE_DEPLOY_HEIGHT could crash a bot into the Z maximum end position.
In these previous versions of Marlin, the homing height was computed by a combination of the above constant adding and subtracting to/from some others, which has since been replaced by the simpler and singular Z_HOMEING_HEIGHT (which works indpendant from the new Z_CLEARANCE_DEPLOY_PROBE):
//#define Z_HOMING_HEIGHT 4  // (in mm) Minimal z height before homing
(G28) for Z clearance above the bed, clamps, ...

#define Z_CLEARANCE_DEPLOY_PROBE   10 // Z Clearance for Deploy/Stow

The absolute value of the maximum bed positions are used in Marlin as sanity check to ensure no axis moves greater than this amount in one movement in either positive or negative direction:
#define Z_MAX_POS 200

If your probe does not function correctly, no ficticious Z_MIN_WHILE_PROBING will prevent a faulty probe from causing a head crash into the bed, so it is not implemented, allowing the Z_MAX_POS sanity check to prevent the Z axis stepper from continuing to run indefinitely during a fauly probe condition.
If your Z_MIN_WHILE_PROBING were implemented, if the printer were powered off (or Marlin crashed, etc) with the head at any Z distance greater than Z_MIN_WHILE_PROBING there would be no mechanism to begin a print on the next poweron, since Marlin will never move in the negative Z axis except during G28 probing and after probing completes successfully.  The only way to recover in this case would be for someone to continually attempt to both home the printer then power-cycle, moving the head Z_MIN_WHILE_PROBING closer to the bed each iteration. This would be an unacceptable user exerience.
Further, if Z_MIN_WHILE_PROBING were implemented, the only percieved safety measure it would add is that during probe failure, the Z stepper would crash into the bed and continue to run for only Z_MIN_WHILE_PROBING stepper rotations instead of Z_MAX_POS rotations.  Regardless, the bed would be impacted so there is hardly any additonal safety added and a stepper driver should not overheat or cause any more damage (other than what was already done to the bed) in a single Z_MAX_POS length of rotations.
For more piece of mind during homing, you may use the Z_MIN_PROBE_ENDSTOP feature with a normally-closed limit switch wired to an available pin on your control board:
// Enable Z_MIN_PROBE_ENDSTOP to use _both_ a Z Probe and a Z-min-endstop on the same machine.
// With this option the Z_MIN_PROBE_PIN will only be used for probing, never for homing.
//
//#define Z_MIN_PROBE_ENDSTOP

Then use the Z_MIN_WHILE_PROBING feature to move the head above the Z_MIN_PROBE_ENDSTOP home position to perform probing.  This will ensure that the printer will crash for only Z_PROBE_OFFSET_FROM_EXTRUDER Z stepper rotations if the probe malfunctions:
#define Z_PROBE_OFFSET_FROM_EXTRUDER 0   // Z offset: -below +above  [the nozzle]

In summary, to prevent the head from crashing into the bed, you must ensure your Z probe is functioning correctly :)


text:
Adding custom M Codes to Marlin
If I wanted to add my own custom M Codes in Marlin - in which source code file would I do that?

This answer is relevant for Marlin 1.x, but not for Marlin 2.x

In the file Marlin_main.cpp on line 7131 there is a switch case:
(To turn on line numbers go to File>Preferences and click Display line numbers.)
case 'M': switch (codenum) {
  #if ENABLED(ULTIPANEL)
    case 0: // M0 - Unconditional stop - Wait for user button press on LCD
    case 1: // M1 - Conditional stop - Wait for user button press on LCD
      gcode_M0_M1();
      break;
  #endif // ULTIPANEL

  case 17:
    gcode_M17();
    break;
  etc.....

Adding another case with an unused number such as 5 and then the code you want followed by a break should do the trick. Ex:
case 5:
   doABunchofCoolStuff();
   myservo.write(thebestposition);
   break;

-AC


text:
Is Tetrahydrofuran viable for dissolving PLA and sticking PLA objects together?
According to Wikipedia, Tetrahydrofuran dissolves PLA. It also apparently dissolves PET.

THF is considered a relatively nontoxic solvent, with the median lethal dose (LD50) comparable to that for acetone.

Wikipedia further states that it's not particularly dangerous provided you keep it away from air circulation, so that it does not form peroxides.

One danger posed by THF follows from its tendency to form highly explosive peroxides on storage in air.

So well, this seems acceptable compared to other possible solvents which are all ridiculously dangerous. The question at hand is now of practical nature:

Is Tetrahudrofuran actually viable replacement for acetone, which only works with ABS?

I am asking because the fact that it does dissolve PLA does not really at all mean that it will work well. It could damage PLA structure, be more toxic than wikipedia says or not dry well.

Personally I'd either use epoxy (since there are plenty of microvoids in the PLA) or a "3D pen" to extrude a little fluid PLA and bond the parts, sort of like a hot-glue gun.

I curious how well it works as well, but it was rather expensive at the couple places I was able to find it for sale at. The prices ranged from 70 to well over 100  USD for 100ml (the cheapest I was able to find any quantity), though the price didn't increase nearly as fast as the quantity went up. The price depended on how carefully it was processed to dry it and what preservative treatments it had. And last, just because the lethal dose is comparable to acetone, it doesn't mean its overall as benign as acetone.

I don't think I'd call THF "not particularly dangerous".  From the "storage" section of an MSDS: "Under normal storage conditions, peroxidizable compounds can form and accumulate peroxides which may explode when subjected to heat or shock. This material is most hazardous when peroxide levels are concentrated by distillation or evaporation. THF should never be distilled to dryness.
Conditions to Avoid: Light, ignition sources, moisture, excess heat, evaporating to near dryness, confined spaces."

According to Shuichi Sato, Daiki Gondo, Takayuki Wada, Shinji Kanehashi & Kazukiyo Nagai: Effects of various liquid organic solvents on solvent‐induced crystallization of amorphous poly(lactic acid) film in Journal of Applied Polymer Science, Volume 129 Issue 3 (2013), p1607-1617source, Tetrahydrofuran is classified as a solvent for PLA. The specific entry on page 1608:
Group  Solvent          Solvent type    dd   dp   dh   dt   Result
Ether  Tetrahydrofuran  Polar aprotic  16.8  5.7  8   19.4  soluble

The values dd dp dh and dt are explained on page 1607:

The effects of 60 liquid organic solvents on PLA are systematically
investigated using the Hansen solubility parameter (HSP). The HSP
is one of the digitizing methods for analyzing the interaction
between polymer materials and organic solvents. In HSP analysis,
all solvents have three parameters: energy from dispersion bonds
between molecules (dd), dipolar intermolecular force between molecules
(dp), and the hydrogen bonds between molecules (dh). All solvents
were characterized by a point in a three-dimensional structure
at which dd, dp, and dh are plotted on three mutually perpendicular
axes. Generally, if the HSP values of the various organic solvents
are near that of the given polymer, the solvent is considered compatible
with the polymer material.

The factor dt is the total Hansen solubility parameter - the bigger this is, the better it is a solvent.
19.4 is a rather good solvent but extremely explosive: in air 20000 ppm (2%) are explosive and thus the allowable concentration in an area is 2000 ppmsource
Alternatives
A similar potent solvent would be Benzene (dt = 18.6) which more easily available and less explosive, but more deadly (10000-20000 ppm fumes) and has an allowable concentration of 500 ppmsource
Ethyl-acetate is also a solvent (dt = 18.2) and more available. It is explosive at an equal concentration as Tetrahydrofuransource, but it has just about half of its vapor pressure (73 mmHgsource  vs. 132 mmHgsource), so can be stored more safely, and is less aggressive on the body. It is sometimes used to Smooth PLA via vapor chambersource, and only comes at a price tag of ca. 90 €/l for the pure stuff and also is used in some nail polish removers, put into a safe mix.
Acetone is classified as a better solvent (dt = 20.1), and it is known to act as a glue and to soften PLA with some exposure time, but from experience, it can't smooth it. It is available most easy (nail polish remover and in the home depot), and is the least deadly option.
Propylene-1,2-carbonate is classed as solvent and a far better at it with dt = 27.2. It has been used as an alternative to Ethyl-Acetatesource and its MSDS is rather gentlesource. It comes at a price tag of 130 €/l for the chemical-grade liquid.
Conclusion
Tetrahydrofuran is not a viable replacement due to its explosive properties. It is not an improvement above Benzene, which at least can be stored safely.
Using Acetone as a benchmark, Tetrahydrofuran should not smooth the surface in a vapor chamber, as it is a worse solvent than Acetone. It should also take longer to soften and dissolve objects than Acetone, but a heated bath or coating the surface with it could help to generate the needed exposure times.
However, its comparable ethyl-acetate has been claimed to be used as a cleaning, vapor smoothing, and brush on surface smoothing agent successfully and can be used better by helping the solubility via heating, which can be done much safer with ethyl-acetate than THF. In a proper chemical mix, its storage problem can be solved too.
A better alternative is propylene-1,2-carbonate, which is a better solvent, and much less dangerous.
tl;dr: No, Tetrahydrofuran is not able to dissolve PLA in a reasonable time1 without heat activation and it has worse characteristics than Acetone. It could arguably be used to weld parts, but Dichloromethane would be more effective.

1 - Sato, Gondo et al. in the aforementioned paper: Solubility tests were performed for 24 h at 35+-1 °C. which means we have a prolonged exposure of a thin film to a huge amount of solvent. how thin a film? Very thin: The PLA films
were prepared by casting 2 wt % dichloromethane solution onto a
flat-bottomed glass Petri dish in a glass bell-type vessel and by drying
under atmospheric pressure at room temperature. Each solvent
was allowed to evaporate for 48 h. The dried PLA films were then
thermally treated under a vacuum for 48 h at 70 °C to eliminate
the residual solvent and to obtain amorphous PLA films. Afterwards,
the thermally treated PLA films were cooled at room temperature
under atmospheric pressure.

The first MSDS I looked at listed a toxicity-based maximum permissible exposure level of 200 ppm, less than 1% of the minimum explosive level.  If you're using THF safely from a toxicity standpoint, it's not going to blow up.  (Storage, on the other hand, is still a problem.)

@Mark Being more than the toxic dose doesn't help as much as you suggest. If you put some in a bottle, nobody cares if the air gap above the solvent contains a toxic level of THF vapour, because you don't stick your head in the bottle. But if the air gap contains an explosive level of THF vapour, you have a big problem. It's not just storage: most prints are porous and will absorb the vapour of whatever you use to finish them. What concentration of THF would end up inside the part?

Acetone does not dissolve PLA at all. The explosion risk is  complicated issue. Generally the inside of the flask does not contain an explosive mix of gas because the oxygen molecules end up in the peroxide compound that naturally forms from THF. However, that compound is quite explosive on it's own.

@TomášZato I have read the paper. Acetone is able to dissolve the film they tested with within the setup, as did THF. from the paper: Solubility tests were performed for 24 h at 35+-1 °C., which means both are a solvent, but neither is a good one. You could use either of the mentioned solvents to weaken the surface layer and allow cross bonding - read the word reasonable time, which refers to the rather slow process.

@DanHulme, referring to the MSDS again, the air space at the top of the bottle won't have an explosive level either: the vapor pressure of THF is rather high, and a rough estimate is that it'll be about 15% THF.  The upper explosive limit is 11.9%, so there's too much THF to explode.  Similarly, that high vapor pressure means the finished part won't have enough trapped THF to be a problem: it will quickly escape into the larger atmosphere and be diluted below the lower explosive limit.  THF is dangerous, but not for the reasons you're focusing on.

Having overlooked propylene-1,2-carbonate, added for that dt=27.2 and relativized some.

Is that benzene the known carcinogen or benzine as in petroleum ether?

@AndrewMorton Benzene as in the non-polar aromatic hydrocarbon related to toluol. Yes, the nasty, carcinogenic stuff. It is also in fuel

From what I have read, THF is not super effective, it seems that Dichloromethane or DCM is actually a better solvent.  Unfortunately I have no personal experience with either.
It is rather nasty though, as the LD50 is just 0.5 to 5 g/kg[1][2].

I'm going to do more research, but so far I can tell for sure that THF disolves PLA much better than how acetone dissolves ABS. So it's super-effective compared to what I've ever seen. However, it's also kinda nasty. Just few minutes of worh with it resulted in nausea and headache. Precautions are advised!


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Is there a way to print on a 3D printed surface?
I have a 3D printed object that I'd like to print on. Adhesive stickers are an option, but as the surface is rounded it's difficult to get a good film to stick well.
Is there any system to print on a 3D object (e.g. ink jet). I need at least 300dpi. Black in the first instance, but color would be nice for future projects.

Also you may try to use a heat shrinkable film instead of adhesive sticker.
There are industrial technologies to print on curved objects, but they are not available for home use.

Have you any experience of letting professional printers print on homemade objects?

Rather than post a series of links for various services and vendors, consider to use as a search term "hydrographic film at home" to find results to suit your purpose. The first search results I found excluded "at home" and indicated it was not suited for home/hobbyist use, but the modification resulted in vendors supportive of home users.
In advanced circumstances, the image printed on the film is topographically matched to the model to which it is to be applied. For home users, I suspect that is somewhat out of reach. Most of the products aimed at the home user are patterns or solid colors, although with care, one could combine films in sequential applications.
Effectively, the process involves a colored film floating on a water filled container. Certain products are applied to the film and to the prepared model to ensure bonding. Additional processes are required to protect the graphic-coated model after removal from the bath/container.
As with the other responses, it's not likely one will achieve 300 dpi resolution without resorting to the topographically matched commercial methods.

There are printer types that can print images into the material as it's being printed. SLA and SLS type printers are capable of this but I believe Polyjet printers are the best suited.
At 300 dpi though you might be pushing the edge of what is capable. to get that fine of detail your best option may be to look into getting a vinyl wrap for your part that is applied after it's printed. If you've seen cars with really high detail images on them, a vinyl wrap is typically how they're done.
Note
I should state that the SLA and SLS embedded images are still in the R&D phases and being experimented with. Possible now, but not in production phase. The SLS version essentially ran another print head over that worked similar to an ink jet before sintering the layers. The SLA version I saw worked somewhat similarly, but had some 'unique' clearing processes.

This answer seems incorrect. I do not think there are SLA or SLS printers capable of printing images.

I should have stated probably that the SLA and SLS embedded images are still in the R&D phases and being experimented with. Possible now, but not in production phase.  The SLS version essentially ran another print head over that worked similar to an ink jet before sintering the layers.  The SLA version I saw worked somewhat similarly, but had some 'unique' clearing processes.

I've undeleted this answer as it is rather interesting. If you feel that I have done so in error, please feel free to re-delete.

@Diesel, could you add some details, as to where you saw these printers demonstrated? Was it at a fair/demostration/early prototype? Why did you delete it? See the chat

There were a couple of people working on the sls printer at UofManitoba in 2012?? (Not sure on the year) as well as a couple of universities in Southern Ontario (Waterloo and whatever the one is just east of Markham, they were playing with SLA). As for why it was deleted, I don't remember deleting this so I can't comment on why I did anymore. What I saw and the people I talked to about it, made it fairly clear the development wasn't near ready for production, just a possible solution. I haven't been active in 3D printing tech for almost 2 year now so its hard to say where that research is now

A possible alternative, depending on the resolution limit of your 3Dprinter, is to embed the text into your design so the final result has the text raised a mm or so above the surface.  You can then easily (!!) paint just the raised surface to highlight the lettering.
This is not going to work for 300dpi, though.

One option is to hire a painter to paint the image onto the surface.
With a skilled painter, you could have a very photorealistic finish. Not sure if this would cost more or less than other routes.

authors: Серега Коваль


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Is this what a 0.1 layer height should look like?
I've done 0.1 before and I think I've gotten better and more smooth results than this:

I think that my printer is having some sort of problem, or the print bed it too low because this was printed at a 0.1 layer height. I think the print should look a lot more smooth than that. I'm using the Monoprice Select Mini.

That doesn't look quite right, looks like the Z-step is larger than 0.4mm. You may need to do some calibration if you haven't yet since you said the bed was low.

Could you perhaps include some textual description of what is in the image? The current title (and wording) of your question is not very friendly to search machines or visually impaired users. Also, it would be helpful to mention the scale of the object (since that would affect whether or not this is "normal").

Have you checked to see if your X-Y gantry system is properly tightened? This looks almost like your layers are shifting in Y while printing. Forward for one layer then slightly shifted back for the next layer.

This may be an effect of the not using a "Magic Number" for your layer height. The Monoprice Select Mini has a z-resolution of 0.04375mm, so layer heights should be multiples of that. (See What are the “magic numbers” on a Monoprice Select Mini?)
If you slice with a layer height of 0.1mm, each layer will be a little smaller (0.0875mm) or bigger (0.13125mm) to get close the the ideal height. The extrusion won't change, causing some layers to be thin and overextruded and others to be thick and underextruded.


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For a larger build volume, what lengths of 2020 aluminium do I need?
TL;DR
How do I upscale a Wilson II? What lengths of aluminium1 do I need in order to achieve a particular (increased/reduced) build volume?

The design of the Wilson II is scalable (source: RepRapWiki - Category:Wilson):

...the design has a parametric build area, meaning it is relatively easy to scale the X, Y, and Z axis within reason.

What does parametric mean exactly, in this scenario? How does one scale up from 200x300x2001? Also, how would that affect the Repetier/Marlin firmware?
Is it simply a matter of maintaining the ratios of the lengths of the X, Y and Z axes constant, or can the ratios be ignored? Is there a formula, or set of formulae, for this?
Has anyone gone beyond the 200x300x200 build volume? I have seen the Scalar M and XL series printers (with the XL having a print volume of 400x300x300) which, while they are not based on the Wilson, also boast of scalability:

Scalar Family 3D printers are "scalable" printers.
Reviewing the idea of a reprap printer, a printer that can auto replicate and scale, we wanted to propose a 3D printer with plastic parts for you to print, and with a way to "scale" easily.

Can one (within reason) arbitrarily section various (supersized) length for the three axes and then modify the firmware accordingly, or is there a set of rules which govern the relationship between the lengths of the three axes?

A simplistic view
As an example, the lengths (in mm) of the 2020 aluminium corresponding to the build volume of 200x300x200 are 330, 500, 400 for the X, Y, and Z axes, respectively.
Obviously, there are some constants to consider for the stepper housings, and idlers, for example. So, assuming that for X, Y and Z axes respectively, the constants are:

330 - 200 = 130 mm
500 - 300 = 200 mm
400 - 200 = 200 mm

If I wanted a build volume of, let's say, 400x500x300 (XYZ), would the new XYZ lengths of 2020 aluminium simply become (by adding the respective constants):

400 + 130 = 530 mm
500 + 200 = 700 mm
300 + 200 = 500 mm

or is there more to it than that?

1 I appreciate that 3030, en lieu of 2020, extruded aluminium may be required to maintain rigidity for larger print volumes

Long story short: ratios can be ignored. You only need to let your firmware know actual size, if it needs so. However, using golden ratio seems quite reasonable.
When talking about rigidity, keeping it will become a real issue at some point and may not be always effectively resolved by merely changing 2020 to 3030. Using 4020 or double 2020 could be better solution to compensate the most common forces during printing.


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What motherboard ID is appropriate for MKS BASE V1.5 in Marlin Firmware?
I'm struggling with my new printer, and I just want to make sure that I have the basic configured correctly.
What motherboard ID in configuration.h is appropriate for MKS BASE V1.5 in Marlin Firmware?

Marlin appears to support older versions of the board (and possibly this one) according to this line
#define BOARD_MKS_13            47   // MKS v1.3 or 1.4 (maybe higher)

in boards.h which can be found here.
The company also has a guide and looks to provide pre-configured (but not fully configured?) downloads of Marlin.  They have different links for different displays but then ask you to change lines manually but don't mention changing the board so I have no idea what they are doing or what is different between the downloads.
It appears either way you go (Marlin from Github or from Osoyoo) you will need to change some lines to get each axis to behave correctly.

A more recent version of Marlin Firmware (version 1.1.9 is the last release of this branch, new developments are done in the 2.x branch) nowadays has a separate board constant for the MKS BASE v1.5 board (BOARD_MKS_BASE_15) as can be found in boards.h.
The following line quotes the constant for this board from the file:

#define BOARD_MKS_BASE_15       405   // MKS v1.5 with Allegro A4982 stepper drivers


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ABS or PLA for structural printed parts?
TL;DR
Is ABS a better material to use for structural parts of a 3D printer, as opposed to PLA?

I have been looking at various suppliers of printed parts for a Wilson II, on eBay.
One supplier supplies all of the parts printed in ABS, whereas another supplier provides the structural parts, which form part of the frame, in PLA, and the remaining (non-structural) parts in ABS. The second supplier states the following:

This kit is printed in two materials, the structural parts are printed on high-quality PLA to provide the necessary rigidity, and the others in premium ABS.

MJRice, who developed the printer, also supplies the printed parts, which are made of PLA.
Is PLA really a better choice for structural components? A quick google lead me to ABS or PLA: Which 3D printing filament should you use?

ABS is going to give your projects better structural integrity and will be more suited to mechanical use given the material can better withstand the elements, but it will also require specific types of printers and printing surfaces. On the flip side, PLA will give you more precise prints and better aesthetic quality, as well as more flexibility with printing conditions if you can do without the strength and resilience of ABS.

Another link, What's stronger? PLA or ABS?, also implies that ABS is stronger than PLA:

The strongest ABS is stronger than the strongest PLA

and

ABS is much less brittle than PLA

although warpage could be an issue...

I choose ABS for it's strength over PLA.  I would love to avoid the warpage/shrinkage problems of ABS.

Heat seems to affect PLA more than ABS (obviously, due to the lower melting point),

FWIW, I know a guy who had a reprap using PLA-printed parts.  He was taking his machine around to do demos and he left it in the car mid-day once.  It melted the parts enough that prints were coming out very poorly even after his best effort at recalibrating the machine.

and as I am in Thailand, my room gets up to 50°C some days (it is unbearable), I wonder if that would be cause for concern?
So, from the above nuggets of information, wouldn't ABS be a better choice? I am surely missing something, as both the second supplier, and MJRice, use PLA.

You might also want to check out PETG as it has next to none warpage and handles applied forces as good or even better than ABS in my personal experience.

@Morothar - Thanks. If you would like to bulk out your comment, and post it as an answer, I'll upvote it. Thanks again.

Thanks, but I don't think my comment qualifies as a proper answer. (Question: A or B? Answer: check out C) :-)

@Morothar - Good point... :-) However, I am now looking to build the parts in nylon, due to the answers below... so whilst my question was directed. specifically, towards ABS and PLA, I guess that I was also open to other suggestions, without realising it. Maybe I should have worded it better.

To answer the main question "Is ABS better for structural parts of a 3D printer as opposed to PLA".
The answer, unfortunately is it depends.
ABS has lower yield and ultimate strengths compared to PLA. This means that at room temperatures, ABS is weaker than PLA. However the difference between yield and ultimate for ABS is much larger than PLA, meaning that ABS parts will deform, noticeably so before breaking. This can be a good thing. If your ABS part is highly loaded, you may want to be able to inspect it for overloading. The plastic deformation that occurs in ABS may be sufficient for you to identify, and modify your parts before a catastrophic failure. With PLA though since the two strengths are quite close, your part would more than likely fail completely without any warning or deformation before it. So in terms of strength, it's a design consideration. Would you rather have a slightly weaker part that shows signs of load failure, or is a catastrophic failure acceptable. There are use cases where either may be better.
As Ecnerwal pointed out, PLA has a lower Tg (glass transition temperature) compared to ABS. If your printed parts are going on a 3D printer and aren't sufficiently isolated from the hot parts (print bed or extruder) then you may end up having some localized deformation. That being said, the extruder is generally pretty localized and likely won't cause you too many issues assuming you're using any of the already available 3D printer designs out there, same for the print bed. However by the sounds of it your 'room' temperature is a fair bit higher than here in North America, by a factor of almost 2! This could cause you some issues if you're printing parts in the high heat with PLA. Your best option would be ABS, but even with it's higher Tg (roughly 90C if I remember correctly) you may still run into issues.
The warping and shrinkage issues mentioned in the question seem to be more about parts being built by a 3D printer. Once the parts are built warpage and shrinkage are essentially a non-issue unless you've heated parts back to within their melting temperatures.
Depending on where you're getting your plastic parts, there may be a third option. By the sounds of it you're looking at building your own printer. You may be able to get the STL files of the printed parts you need and then have someone print them for you in a stronger material such as Nylon.
Assuming alternative materials aren't an option I would personally suggest going with ABS for your use case. My reasoning is purely due to the potential operating temperatures. While 50C is below the Tg for PLA it's getting very close.

Nylon, I had not considered that.

To answer your question, ABS is better than PLA for parts however I wouldn't use ABS for that, I would use PETG for structural parts.
PETG is more durable than ABS or PLA. PETG is more flexible than PLA and it not brittle like ABS. What makes PETG so good is the G! G stands for Glycol, this is added to prevent the material from crystallizing when over heated. While some companies say it is "Food Grade" you really need to be careful as note every factory produce it the same.
When I started printing I only used ABS, I thought it was better because it was stronger than PLA, so I just put up with the smell of ABS.
It wasn't until I bought my second printer that I found out about PETG. They guy that makes my printer used to work in the plastics industry, so he gave me some info on the filaments on the market.
Now I use PLA and PETG. PLA for testing and playing with different models and PETG for anything I want to last or will be used in hot environments (like in the car).
Printing with PETG is very easy, a lot easier than ABS. It sticks to the bed very well (I still use Glue stick though) and no smell. Temp depends on your printer. I use an ExtraBot, I run the Extruder at 220°C and the glass bed at 80°C
There are a lot of write ups on PETG, many different settings/temps they recommend. Honestly, watch while you print. Start off at 220°C and if you see bubbles, drop the temp in increments, if you see it not sticking to the bed or the nozzle is clogging up, increase the temp.

Thanks for the heads up on PETG. Could you edit and expand your answer a little, to explain why PETG is better (properties, specifications, personal experience?)

Done, just updated it for you

Isn't flexibility something that you specifically want to avoid in structural parts for a 3D printer, where a very stiff structure improves accuracy? A lot of printers use aluminum extrusion exactly because it's so stiff.

50°C is hot for you. PLA's glass transition temperature is 65°C. A car in the mid-day sun can get very hot indeed.
As to the question of "stronger" - if the part is designed to be strong enough for its use in PLA, it will be no better in "stronger" ABS. If the PLA part will be "more precise" and "less warped" - that may well make it better for its use. Other than a widespread community dedication to self-replication, (or mostly self-replicating with some metal parts) there's plenty of arguments for making most printer parts out of machined metal, for that matter - much stronger than ABS or PLA.
Brittleness likewise might matter if you were planning to drop the printer; but should not matter in use if the part is designed for the forces it will see in the material it's designed for. Looking at older technology, many machine tools are made of cast iron, which is quite brittle, rather than steel, which can be less brittle depending on how it's processed. If the part is designed for the job and used/handled in a reasonable way, "brittle" is not an inherently bad thing, and a thin steel part that flexes is a worse thing than a thick cast iron part that flexes less.
As for

withstand the elements

that appears to be a reference to outdoor use where PLA will break down - but if you are not leaving your printer out in the rain (which will be bad for many other parts unless you do a lot of engineering to protect them) that should be of little concern.

Actually, Both PLA and ABS could use for structural parts. PLA has high strength and is brittleness. ABS has better thermal resistance and durable. PLA and ABS are the main types of 3D printing material, each has cons and pros.
If you want to choose which type, you need to know the detailed application.

Welcome to 3D Printing SE and thank you for your contribution. When you get a chance, please take the Tour to understand how the site works and how it is different than others.


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Bed won't switch off after Marlin firmware update
After I updated the firmware on my Prusa i3, the Bed won't switch off anymore. It worked perfectly before the update, but now, the moment I power up my printer, the LED on the bed turns on and it starts heating up. The manual control in Repetier Host doesn't turn if off or on and I even tried g-codes M140 S0 as well as M0, but it does not switch it off.
Edit:
I have an Arduino Mega2560 with a RAMPS shield. The Marlin firmware came pre-configured from the store I bought the kit from.

What electronics do you have, and is your configuration of Marlin appropriate to the electronics?

@TomvanderZanden I edited my question to include info on the electronics

This was actually a coincidental situation where I somehow damaged the RAMPS board around the same time I reloaded the firmware. Replaced the board and it works correctly now

It sounds like the pin configuration in the firmware you flashed doesn't match your hardware. Heaters should never be on by default and M140 S0 should always turn off current to the bed. What you describe sounds like the firmware is sending power to a pin that it believes is something other than what it is, either because the bed is on a fan pin (like D9) or because the firmware thinks D8 is something other than the heated bed.
If it worked before, your original firmware was configured to match how your board was wired, specifically which pins were mapped to what hardware. If you're confident that the new firmware pin configuration is correct, you can ignore this theory. Otherwise you should nail down which D8/D9/D10 pin maps to what hardware and resolve the mismatch.
On RAMPS, pins 8, 9 and 10 are typically used to control fans, hotends and heated beds and you define this behavior in configuration.h. If you flashed from source you should review configuration.h and ensure it matches your hardware. This likely means setting the MOTHERBOARD to the value that matches how pins 8/9/10 are wired. See this section (or something similar) in configuration.h to get started:
// The following define selects which electronics board you have.
// Please choose the name from boards.h that matches your setup
#ifndef MOTHERBOARD
  #define MOTHERBOARD BOARD_RAMPS_14_EFB
#endif

Thanks, but this isn't the problem. I actually loaded a blank sketch (the blink sketch actually) to the Arduino and that specific pin was still on, so it seems to me that I somehow shorted the RAMPS board at about the same time I loaded the new firmware. I spent some more time troubleshooting and because it would always switch on when I plug it in, I also now managed to short out the heated bed, so I'm replacing both the bed and the board this weekend. Hopefully there is not some still undiscovered root cause


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Pronterface won't connect to my Anycubic Kossel Linear Plus
For the Anycubic Kossel Linear Plus I have to upload data to the 3D printer from a software called Arduino and then close it. Then I open Pronterface and put in the right port and baud rate that is in the Arduino files and then click "connect". Afterwards it says
connecting...

and that is all it does and doesn't fully connect to the printer. I've tried changing the baud rate and port in Pronterface, Arduino and the bit rate in the Device Manager but nothing works.
Any suggestions on how to fix this?

What happens if you disconnect and then reconnect the USB cable? Does Pronterface connect then? Has it ever worked?

I know this is coming very late, but I'll post anyway in hopes that it may help somebody else experiencing the same frustration.
I received all of the same suggestions again and again on the forums -- about baud rate, COM ports, and a lot else which failed to get Pronterface to connect.
At last I posted to the Anycubic User Group on FB, and quickly received what was in my case the solution -- and so ridiculously simple.
I was told to hit RESET two or three times on Pronterface after hitting CONNECT.  Yup, that did it!
Good luck!!  :D

I know this may be a little late, but I bought the same printer and found that I had problems also. To fix this connection issue I first made sure I had no arduino programs open that were trying the connect to the printer. These would not allow Pronterface to connect to my printer. Then if I still had issues I opened up task manager on my computer just to make sure I had no other programs trying to communicate with the printer. Then if it still can't connect I closed Pronterface and reloaded it a couple of times.

Only one application can access the Arduino Mega board, via the COM port, at a time. Sometimes, the software can get confused, and keep hold of the COM port, although this is unusual.
For example, if you are connected to your board via Pronterface, and without clicking on Pronterface's Disconnect button first, you then try to upload some code to the Arduino via the Arduino IDE, the Arduino IDE will just sit there complaining that it can not connect - usually with an error, or a timeout message, like this:
avrdude: stk500v2_ReceiveMessage(): timeout

See the video tutorial, #18: Calibration, by BuildA3DPrinter. It is a long video, but extremely informative. At 2:20 he has this exact problem. In fact, throughout the video, the instructor constantly reminds the viewer to disconnect from Pronterface before attempting to upload new firmware via the Arduino IDE.
Now, I know that this is the opposite of your issue, as your can not connect using Pronterface, after using the Arduino IDE, as opposed to the other way around, as shown in the video. However, the solution is most probably the same... Momentarily, disconnect the Arduino board from the USB (i.e. unplug the USB cable for a few seconds and then reconnect it). Then, without using the Arduino IDE, now try to connect Pronterface. It should now work - assuming that you have selected the correct COM port, baud rate etc.

I recently purchased and assembled the Anycubic Kossel Delta printer and ran into the same issues.
I found that if I tried to connect with "COM 1" first, it would error out, then when I switched to "COM 4" (the correct port), it connected. Weird, I know, but it works.


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Settings for Taulman 618 Nylon
I would like to know what are the best settings for Taulman 618 Nylon filament? In particular, the print head and print bed temperatures.

Best for what? These things depend on a lot of variables (like your printer, print speed, layer height, etc...).

Hi Cynthia, and welcome to Stack Exchange - 3D Printing. Please could you expand your answer, with more detail, as Tom has requested in his comment. The more information that you provide the more likely it is that someone will be able to provide you with an accurate answer. Also, take a look at How do I ask a good question?.  Thanks.

240°C, lots of cooling.
See Material Specification Print Sheet - Taulmann 618 Nylon.

Note: sometimes, for Nylon, I tape some fine sandpaper, grit up, and print on that. This gives more texture for the Nylon to adhere to.


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Second layer of ASA print 'runs'
I am using a Prusa i3 MK2 to do a print in ASA, and I'm having a problem where on the second layer the plastic 'runs' into lines across the direction the head travels. It looks like the plastic is being repelled by the previous layer and running together due to surface tension, but I may be wrong about this.
I thought I had managed to solve this problem previously by reducing the temperature to 230 °C (1st layer) / 225 °C (other layers), but having changed some of the other settings this is no longer solving the problem. I have tried reducing the temperature as low as 215 °C / 210 °C, and this is still happening.
Here is a photograph of the first and second layers:

The direction of head travel for the first layer was bottom left <-> top right, and for the second layer top left <-> bottom right.
The settings were based on the standard Prusa i3 MK2 Slic3r settings bundle for ABS filament with a 0.05 mm layer height, modified as follows:

print temperature reduced to 230 °C / 225 °C
fan speed increased slightly to 15 % as on 10 % the fan doesn't start.
layer height for first 14 layers: 0.2 mm
extrusion widths set to Slic3r defaults
various print speeds reduced, mainly the travel speed.
number of top and bottom layers reduced because of the increased layer height.

The reason for increasing the layer height for the first 14 layers is that the print is a piece of mixed raised text and braille lettering intended to be inset into a larger sign. I want fine detail for the top layers with the lettering, but high speed for the lower layers that are more structural. I am inserting an M600 change filament manually into the G-Code file at the point where the lettering starts.  I have so far managed to produce one successful print - see the image below. The reason I am still playing with the settings is that the good print wasn't in high enough quality, and there was some slight stringing between letters.

The good print was based on a 0.1 mm layer height for the lettering, modified to 0.15 mm for the lower layers, with a temperature of 230 °C / 225 °C.

For the stringing issue, you may want to try increasing your retraction distance. From the looks of the image it only is off by a small amount maybe 0.1mm. Are your X-Y belts tight? It looks like you might have a bit of extra play on the printer axis that was parallel to the writing direction.

I've now worked out the reason for the plastic 'running' on the second layer. It is because of the way that I prepared the G-Code file, using the option in  Slic3r which lets you alter the layer height for certain layers in the print. The problem with this appears to be that there are other settings which are not altered at the same time for the thicker layers. So the first half of the file ends up printed using the settings that work for a 0.05 mm layer height, but with the layer height set to 0.2 mm.
I have prepared a new file by rendering two G-Code files, one using the Prusa settings for a 0.2 mm layer height, and the other using a 0.05 mm layer height. I then merged these manually by looking for the layer change at 2.8 mm in both files and appending the end of the 0.05 mm file to the start of the 0.2 mm file. (I found the layer changes by using Slic3r's custom G-Code option, and adding custom comments into the G-Code which included the layer number and height on every layer change). Then I inserted an M600 'Change filament' instruction at a height of 3.05 mm, where the writing begins.
When I print this file, the problem with the plastic running together on the second layer disappears.


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Scaling/size issues in delta printers
So here How to achieve dimensional accuracy of printed parts the Cartesian printer approach to accurate sizing is covered. And deltas get a footnote of being a whole other ball of wax - so let's look at that wax ball.
I'm currently resurrecting, or erecting, depending how one looks at it, a poorly documented Chinese printer (purchased in China by a Chinese student and abandoned in the US after graduation) that appears to be based off a Rostock mini. Z 204mm, X Y 100mm radius or 200 mm diameter, Bowden tube.

It appears to be equipped with an absurdly small nozzle (lacking a good way to check that precisely yet, feeding suggests possibly 0.1mm, and no, the vertical resolution is not nearly enough to make that in any way reasonable), which is obviously fixable if the rest of it can be made to work.
Yesterday we got it to the point of (very tediously with tiny nozzle) spitting out a test cube, which was 17 by 17 by 20 mm - undersized in XY, accurate in Z. The last bit makes me pretty sure the steps/mm are right on the steppers, but obviously something is off in the geometry (measured, no documentation for this exact printer can be found, at least by non-Chinese-speaking/reading me - it being utterly un-branded does not help.)
A second test cube was produced with scaling set to 20/17 (1.176) in the XY directions, and that seems to be accurate at least to non-precision measurements. I'm now contemplating "what likely needs tweaked, and in what direction" for the delta geometry - I'd say the rod eye-to-eye measurement (85mm, IIRC) is fairly decent, the offset from rod mount at carriage to rod center is not too terrible, and I have low confidence in the rod mount at printhead to nozzle - so that's the one I suspect most.
tl, dr:But I lack an intuitive understanding of how each of those parameters (offset at carriage, offset at printhead, and arm length) would affect the printed size. I'll come back and edit in what we currently think each is. Rather than depending on scaling in the slicer I'd like to seek the "right numbers" but when at the limits of available measurement precision, having an idea how and in what direction incorrect offsets or arm length affect the print size would be good, rather than just blindly changing numbers and hoping.
I also have some other "print quality" issues and a bed leveling issue which will be other questions when I can sort that out.

This is a very detailed post, and interesting to read, but what is the actual question? Could you provide a TL;DR summary?

As requested - I'd like to know how and in what direction incorrect delta parameters will affect the as-printed size/geometry, so I can try to tweak mine to be correct, without a full fledged metrology lab to get more dependable measurements of things that are difficult to get accurately by eyeball and calipers.

Issues in X-Y size on a Delta are usually the result of an incorrect diagonal rod value in the firmware.  This should be easy to fix assuming the rods were built together.
The formula for this is (20 in this case is your test print X-Y):
New DELTA_DIAGONAL_ROD = 20 / measured_length * Original DELTA_DIAGONAL_ROD
I found this information (here), this site also has more information on setting the radius and other delta specific issues.
If you encounter issues with the size of the rods you should build new ones using a jig.  There are several (here's one) I found on Thingiverse but they require printed parts and they do all the rods horizontally which I think would be tough to keep equal. I would use something similar to this picture but with a longer rod/bolt so you can fit all rods on the same time.  When I did my Kossel Mini I used a piece of the extrusion with bolts coming off of it to keep the rods consistent.

For the other issues you mention you should open another question specific to each issue.

Thanks; I have been around stack exchange long enough to not only know that those issues  are separate questions, but to mention that they will be separate questions when I get to them; and not to ask them until I have done enough background to make them worth asking.


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How long is an extruder's/nozzle's life?
I've been using a printer for several years now and I've never replaced any of my extruder hardware (nozzles, steppers, gears etc.). I was wondering how long you should expect your extruder hardware to last? Is it indefinite, or are there normal life expectancies on them?
Also, what signs should you look for, in your prints, that would suggest that your nozzle is starting to wear out?
I'm more interested in the parts that contact your filament directly - I'm painfully familiar with replacing gantry parts (X-Y belts and pulleys).

This is highly dependent upon the type and quality of filament you use.
Exotic materials such as wood, metalic, or otherwise infused plastics can potentially wear out the inside of the nozzle and at the very least leave deposits of composite material in the nozzle. This can lead to more frequent or irreversible clogs. You may also notice your prints becoming "stringy-er" (sorry for lack of vocabulary at the moment) as the volume of your nozzle reduces with more deposits sitting in the basin of the nozzle, therefore leading to lighter extrusions against what your slicer is expecting.
Lower quality materials (common ABS/PLA) can also have an effect on your nozzles life span. So can good quality filament, don't get me wrong. However, lower quality materials have a tendency to go through much more drastic material changes during the printing process than better quality filaments. For instance, a lower quality PLA may not be 100% PLA. It could have 10% Nylon, 5% ABS, 0.1% operator's BandAid, and 83% PLA. Well, the 17% of the filament that isn't PLA has the potential to clog the nozzle just as easily as the exotic filaments. This is why it's so important to verify the quality of your source of filaments.
Some signs that your nozzle may be wearing:

It simply clogs more frequently
The printed part looks "stringy" or "bubbly". The "stringy" effect is that the extruder is not extruding at a fast enough rate for the speed of the motion, which is common if your extruder is about to clog, your filament is crappy quality, or your slicing settings are invalid for your machine. The "bubbly" effect can be from an overheated extruder or another sign that your nozzle is about clogged.
Your filament begins curling around the nozzle as it initially comes out. Typically there is a burr or something that catches the filament on its way out that you can simply take a small file to grind it off, but sometimes it may be because there is the build-up of deposits towards one side of the basin.


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P3Steel v4 w/ 20x30 cm bed, or 2.5.1 w/ 20x20
I'm building a new printer after having an Anet A8 for about two months and getting a feel for what I want. I'm planning to buy a P3Steel frame; but can't decide which version to get.
There are one or two prints I would like to make that are larger than 20 cm in length; but I could always do these in multiple pieces.
What I'm wondering is how serious are the trade-offs I would be making for a larger bed? I would think I would need thicker linear rods for the 510 mm length y-axis; and the bed would also have a large amount of inertia so that could slow down printing. Does anyone have any experience with this size bed in a moving y-carriage scenario? Also how thick of rods should I get? Orballo printing is saying 8 mm is fine but the research I've done implies that you shouldn't really go over 200-250 mm unsupported for that width.

Go for the P3Steel v4 (20x30). The extra print area is worth it. There is a Polish supplier, Printo3D, on eBay that has the cheapest frame, and parts - cheaper than the Spanish supplier. That is where I got mine from. See Frame Prusa I3 P3Steel v 4.0, 300mm x 200 mm, which costs around £80.
This kit uses 10 mm smooth rods for the Y axis:

Smooth stainless steel rods:

2x Ø8x385 mm for X-Axis
2x Ø8x320 mm for Z-Axis
2x Ø10x520 mm for Y-Axis

Threaded stainless steel rods:

2x M5x300 mm

With respect to the Y-axis carriage, the steel carriage does add a lot of weight/inertia, you are correct. This may or may not be an issue, depending on your steppers motors that you choose1, and their torque. That said, the 3 mm steel print bed/Y-axis carriage, is ridiculously heavy, and it would be most wise to substitute it for an aluminium, plywood, or some other lightweight solution.
Apart from that the 3 mm steel frame is fine and as solid as a rock. There are a number of aluminium 20x30 print beds/Y-axis carriages available on eBay and Amazon. A thorough search should reveal a few. There are also composite Y-axis carriages, I found a supplier in the Ukraine, tehnologika_net, who, last year, had a number of different types at a reasonable cost - in fact they were the cheapest that I found.
As an aside, I built mine sourcing all of the parts separately. It was a bit of a task, but an educative one. The process certainly made me understand the ins and outs a lot better than purchasing a ready built, or complete kit, 3D printer.
I have written up some blogs regarding the kit that I purchased, see P3Steel from Poland – A tale of despair, dismay and woe. Ignore the depressing title, it really isn't that bad.
See also Heatbeds. At the bottom there are some links to various alternative Y-axis carriages. However, some of the links/items may no longer be available.
You may also find this question of mine useful, Z axis top brackets, of P3Steel, differ between v1.x/2.x and v4.

There are a number of modifications to the standard P3Steel, that may well be worth considering. In particular, you should note the Toolsen Edition MK2, see P3steel toolson edition MK2 (in German), and P3steel - toolson edition. I have written about these, and more, see P3Steel version 4 modifications. In summary, these are:

Bowden extruders
Endstops
Endstops by Toolsen
Optical Endstops by Toolsen
Idlers by Toolsen
Extruder by NWRepRap
Lead screws
Aluminium/Composite Y-axis carriage

1 I got the Rattm 17HS8401 steppers. See RepRapWiki - Nema17. The recommended steppers are high torque:

Kysan 1124090/42BYGH4803;
Rattm 17HS8401, and;
Wantai 42BYGHW609

However, motors close to NEMA 17 size, with approximately the
following specifications, can also work:

1.5A to 1.8A current per phase
1-4 volts
3 to 8 mH inductance per phase
44 N·cm (62oz·in, 4.5kg·cm) or more holding torque
1.8 or 0.9 degrees per step (200/400 steps/rev respectively)

thank you, this is exactly what I was looking for. And I suspected that steel carriage would be overly heavy; thank you for confirming.

Do you know what specifications the stepper motor would need for the y-carriage? I bought a working but otherwise terrible https://www.3dprintersonlinestore.com/full-acrylic-reprap-prusa-i3-kit off a friend for 60$ with the idea of using the non-frame parts for my p3steel build. I'm not sure what the specifications on the motor are though; or for that matter what the desired specifications are.

@JonathanBayer - I got the Rattm 17HS8401 steppers. See Nema17. The recommended steppers are high torque (44 N·cm (62oz·in, 4.5kg·cm) or more holding torque): Kysan 1124090/42BYGH4803, Rattm 17HS8401, and Wantai 42BYGHW609. I have updated my answer with this information.


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Can you print at 0.3 mm with a 0.2 mm nozzle?
I recently ordered some spare E3D 0.4 mm nozzles. However, there was a mix up at the factory and they delivered 0.2 mm nozzles instead.
I usually print at 0.3 mm using a 0.4 mm nozzle. Can I still use the 0.2 mm nozzles to print at a resolution of 0.3 mm?

To get the best results, the plastic coming out of the nozzle needs to be squished/ironed down by the nozzle. If you are using a higher layer height than nozzle size, this does not happen. Instead, you are taking a 0.2mm diameter string of plastic and folding it back onto itself to create a thicker 0.3mm bead.
Triffid_Hunter's calibration guide recommends using a layer height that is not higher than 80% of your nozzle size, so with a 0.4mm nozzle you should not print layers thicker than 0.32mm, and with a 0.2mm nozzle you should not print layers thicker than 0.16mm.
While it is not impossible to print thicker layers with a smaller nozzle, the results won't be as good. Moreover, if you are used to working with a 0.4mm nozzle then swapping to a 0.2mm nozzle may take some getting used to, as printing with smaller nozzles is more difficult (for example, the smaller the nozzle, the higher the likelihood of clogs).

And the print time will be much longer.... You only get a quarter the plastic at half the diameter, and you have to make many more passes. Your feeder may complain/skip/chew when trying to feed at 0.3 rates into a 0.2 nozzle, as well. That's 2.25 times as much plastic as the nozzle would be expected to feed.


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My Anet A8 prints have been looking squished
I have recently purchased an Anet A8 but have been wondering why the prints look squished and have tiny balls on them.
I am using 1.75 mm cheap PLA bought from eBay and have also had problems of filament oozing out of the print block.
]1

Also, I think that the head is not moving enough up each time.

It could be that cheap filament has inconsistent diameter, or your calibration is over extruding, or you have something loose that needs to be tight.  It's hard for me to tell precisely from just these images.  In your shoes, I would print 20mm x 20mm x 10mm, 100% infill boxes until I got it dialed in so that it is square, fully filled in, but nice and flat.
If they're coming out square and staying stuck to the build plate properly, but are bumpy and overfilled, then you're over extruding and you'll want to either recalibrate e-steps or if they're correct, adjust your flow rate in the slicer (down).
If they aren't square then you need to square up your frame and tighten it and the belts.
Etc.
But my first guess is that you're extruding too much plastic since I'll bet they were flatter when they were still on the build plate, yes?
On the question of ooze: you'll always get some ooze.  Molten plastic and gravity means some will ooze out pretty much no matter what.  What you need to worry about is when this results in stringing or unwanted lines on the surface of the print.  These things you address with retraction (which reduces the pressure on the nozzle during travel moves, but can't stop gravity) and for the surface problem various travel, z-hop and combing strategies depending on your slicer.

I turned down the flow and it did help but then the thermistor broke, shorted and destroyed the motherboard D: waiting on the new motherboard as I have no voltage coming trough Extruder thermistor.

You may be having an over-extrusion issue, you should check the flow rate in whatever slicer you use.
You should also check to make sure that the filament diameter you are using matches that of the diameter setting in your slicer.

So, I think iv diagnosed the problem with the help from you and some guys from Thingiverse https://www.thingiverse.com/groups/anet-a8-prusa-i3/topic:15005. I think it is a combination of over extrusion and the hotend. The Hotend was leaking so I have fitted a new one. Unfortunately, the thermostat has broken so I have bought a new one. I will keep you updated and thank you for all of the support, Thomas.  Hotend Leaking: https://i.stack.imgur.com/yYqd1.jpg

First, I would check for bed adhesion issues. I would then check the hot-end, when it is warmed up, for any loose parts. I have fixed such issues with a piece of PTFE tape.
I would also check the filament cooler parts, or proximity sensor (if you have one), for possible drag on the printed sections during printing.

I have always wondered if PTFE would work as it melts at 204 degrees C and I am printing at 200. Do you think it is a viable option?


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Delta printer not responding to changes in DELTA_RADIUS
As mentioned in my previous question, I have some bed-levelling issues with my printer. Following the link in @tjb1's answer I figured they were all about to be solved - just follow the steps and bim, bam, flat printing aligned with the plane of the bed. I was wrong. Firmware is Marlin 1.1.0-RC8
From minow.blogspot.com:

For Marlin in Marlin.ino.Marlin.pde
DELTA_RADIUS is DELTA_SMOOTH_ROD_OFFSET - DELTA_EFFECTOR_OFFSET
  -DELTA_CARRIAGE_OFFSET
              To correct the problem, the best course is to change one of the variables set earlier to force the value of DELTA_RADIUS to
  increase(to lower the extruder nozzle) or to decrease (to raise the
  nozzle).
To lower the extruder nozzle increase DELTA_RADIUS by increasing
  DELTA_SMOOTH_ROD_OFFSET(Marlin) or PRINTER_RADIUS(Repetier).
To raise the extruder nozzle,  decrease DELTA_RADIUS by decreasing
  DELTA_SMOOTH_ROD_OFFSET(Marlin) or PRINTER_RADIUS(Repetier). For your
  first cycle, if you are above the build surface, increase DELTA_RADIUS
  by (about) the same amount.  If the extruder nozzle hits the build
  surface, decrease DELTA_RADIUS.
Next, repeat the ABC tower calibration process.  Changing the
  DELTA_RADIUS changes the tower calibrations, so you must cycle through
  the process of adjusting the ABC buttons/scripts again.  And when the
  ABC towers are set, test the center D button/script.
You may have to repeat this a few times with smaller changes to
  DELTA_RADIUS, but eventually, the drag on a piece of paper should be
  the same at all four locations.  Now the printer knows how to print
  flat at a given Z height.

So I did that. It's about 5-6mm high in the center of the bed. On point in front of the 3 towers. And it stays pretty much there (less than one 'precision' business card movement, if any) when DELTA_SMOOTH_ROD_OFFSET is increased, increased more, or decreased, for that matter - we started wondering if there was a sign error issue and tried the other way.
There is mention on the page of "turning off EEPROM" lest values be over-ridden by those in EEPROM, but the text appears to suggest that it's a Repetier-firmware-specific problem. So I was not expecting to have it in Marlin. Does it also apply to Marlin, or:
TL;DR mode: why would changes that should affect the "DELTA_RADIUS" to get the printer on plane with the bed be ineffective?
]3

OK, so a little more poking around finds that it does seem to be loading values from EEPROM and ignoring the configuration files. So that's not Repetier-firmware-specific.
...and I found M665 in G-code which lets me just set a value for it, then M500 saves it to said EEPROM. And it's making a difference (so much of one that I may need to reset Zmax before I can actually adjust it all out as the endpoints on the bed are now off, but they are all 4 much closer to being off by the same amount!)

I used this post to help me with my own printer, and this is what I found:
Adjust the firmware to your needed values and hit M500 before you start moving around the bed. (M500 saves the firmware values to the EPPROM, so you always have the freshest values in there) it took me ~1 hour to calibrate my printer after discovering this.


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Nozzle moves very slowly from home to start position
I´m currently working on a custom delta printer running Marlin 1.0.2 firmware. To control it I´m using the Repetier Host software with the onboard Cura software to slice my objects. The printing works fine but it takes the nozzle nearly 5 minutes to move from the homing position at 250 mm to the starting position of the print near z=0.
I already tried to increase the travel speed but nothing changed. Can you guys please tell me how to increase the speed of my nozzle to move down to my starting point of the print?

Please share the exact G-code that causes this problem. Without it we just have to take guesses at what is wrong in your settings.

As @TomvanderZanden says, the problem and the fix are most likely in your "start gcode" setting.  You said "increase travel speed", but I think you meant you changed the travel speed setting in Cura, not in the specific line in the "start gcode" that actually does the travel from home to z=0.  The start gcode will have something like G28 X Y Z F{some number} maybe twice, once fast and once slow. And then it may have a move to some start position (G1 X0 Y0 Z5 F{some number}) and it is that feedrate that matters here. (Perhaps you're using a snippet of start.gcode meant for a cartesion printer.)

Is this during a G0, a G1, or a G28? Your max G0 speed may be set low; have you tried adding an F value on that homing move?

Without the G-code this is guessing, to follow up @MarkWalker, start G-code for CuraEngine from within Repetier-Host is found here.

I had the same problem, and I solved it by changing the Z-Axis Feed Rate to a much higher value (1000 mm/min.) in Repetier Host via Config -> Printer Settings -> Printer.

I think the travel speed and z axis feed rate are different things though; the travel speed is used during the print to move the print head without printing while the z axis feed rate is used before the print starts.
Either way, I've encountered the same problem as OP and my answer worked for me.

my bad, I stand corrected, +1! :)

I would guess (without G code) to change start G code. You should find it in Cura, the feed rate should be low there.
Try other slicer and print from SD card.
Try using other software. Try Cura it self if SD card printing is not available.

Picture is just an example what to look in Repertier or Cura.

Please answer this with the respective given stats in mind: OP already increased travel speed and uses Marlin 1.0.2 with control via Repetier Host (with Cura Engine). Your picture is not Repetier Host.

The problem OP has is to do with Starting G-code, nothing to do with software. Offered to OP solution, change slicer and check if it's the same, look for starting G-code and change it because that's where the problem lies.

Try changing the travel speed in you r slicer, if that doesn't work , try changing out the motors for newer ones.

As stated in the question, they already tried that. Since after the initial travel move everything apparently works flawlessly, changing the motors seems pointless.


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Can I repurpose the ISP pins in the lower right corner of the Melzi board?
Background: I have many years of experience with AVR and ARM Cortex PLCs and I feel very comfortable using them in projects but I am not an EE or SE. So, if I make a mistake or misunderstand something, keep that in mind. Thanks.
I cracked open the case on my Maker Select v2.1 and I noticed that I have a 2x3 header that is labeled ISP. This is fairly standard for the AVR PLCs and the Melzi board that I have uses the ATMEGA1284P.
I have asked at numerous forums and nobody seems to really know the answer (the downside to RepRap--people use but don't fully understand).
I'm wondering if I can tweak the Repetier firmware (I'm using the stock version 0.91) to use the ISP headers as a standard SPI bus. It has the SCK, MOSI, and MISO pins but it doesn't have the SS pin.
What I want to do is put a port expander on the SPI bus and break out additional usable GPIOs.
So, is there a hardware limitation or any other reason why I wouldn't be able to repurpose the ISP headers into an SPI bus?

In theory, you can; but, you may need those pins to attach an external programmer to bring your system back to life when playing around with the code.
Here are a couple of articles that could help if you still want to pursue that path:

Can SPI programmer interfere with other components on same pins?
Can I reuse ISP pins for other tasks?(Target: Atmega164p)

Another option (the one I chose) is to just buy a RAMPS board set.  I got one on ebay for $19 and it have lots of more options for IO.  That way you can play and still go back and plug in your stock Melzi and print whenever you need it.
I got all this for $40 - boards, display, cables, power supply, and even shipping

Here is a really nice detailed description of converting a Duplicator i3 from Melzi to RAMPS.  The process would likely be very similar for your printer.
The biggest challenge will likely be setting up the firmware
BTW, what printer did you get?

Fantastic answer! I ended up getting the Monoprice Maker Select v2.1 back in November. Couldn't beat the price and I saw it had a very large community of support. Made me really happy to see it's all parts that I've worked with and used before (Arduino and components).

I have a Tronxy X3.  My printer has Repetier Firmware.  I have found it on GitHub; but, that code base seems dormant.  Marlin Firmware has a very active Open Source development (https://github.com/MarlinFirmware).  I look forward to playing with the code and it looks like Marlin would be a better place to do that.  It appears that either firmware will run the printer well.

I like the simplicity of that design. No frills, no additional things to get in the way, just all that is needed to make it work. It looks like it has a rather large build space, too. I haven't seen too many people with a Tronxy--what do you think of it?

@Rincewind I like the X3; but, it is my first printer so I don't have much to compare it to.  The one thing I can say for sure is that it would likely not be a good option for someone that doesn't like fiddling with things.  It does have a few issues; but, there is a strong maker community around it so there are are fixes for all the issues.  The reason I wanted is because I wanted to fiddle and the open design makes that easy to do.  I am very happy with the printer and have not had a print fail yet.

@markshancock, Repetier is the firmware shipped with the Maker Select (Wanhao rebranded). Repetier is FAR from dormant, and, frankly, has better bed-leveling.

@MarkWard Comparing the two firmwares on GitHub Repetier has 39 contributors and 999 commits (10 in the last 6mo) where Marlin has 415 contributors and 10,196 commits (437 in the last 6mo)

authors: 강남오피JJhaha닷ga강남안마


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How long are the carbon fibre rods for a Travelling Kossel?
TL;DR - For a given Kossel frame size (w.r.t. the vertical and horizontal frame lengths of the aluminium extrusion), what would the length of the carbon fibre rods be?

A case in point, from RepRapWiki - Kossel, there is an intriguing note about a scaled down Kossel:

Optionally scale down to a Traveling RepRap that fits within IATA hand
  luggage size limit (see transportation):

Frame height: 550 mm.
Footprint: triangle, 270 mm width, 250 mm across (210 mm 15 x 15 mm aluminium extrusion like OpenBeam + printed corners).

However, there is no mention of the length of the carbon fibre rods (carbon tubes).
Now, as per my previous question, For a larger build volume, what lengths of 2020 aluminium do I need?, is there a formula or ratio by which one needs to abide? Whereas in my previous question, the answer was along the lines of: Not really, you can use any lengths, within reason, and account for it later in the firmware, I would imagine that the Delta aspect of the printer is somewhat more exacting.
I have tried googling for further information on this Travelling Kossel, but found nothing, except for the information of RepRapWiki.
Looking at the corresponding lengths (vertical/horizontal) of the aluminium versus those of the carbon fibre rods for the Mini and XL:

600/240 mm versus 180 mm
750/360 mm versus 300 mm

I really can not see what the (trigonometric) relationship is, and therefore can not deduce the lengths of the carbon rods for the Travelling Kossel.
Unless it is simply that the carbon rods are 60 mm shorter than the aluminium horizontals? Is it really as simple as that, or is this just a coincidence? In which case, would the carbon rods be (210 - 60 =) 150 mm?
By extension, imagine if you wanted to build a Kossel XXXL, with a horizontal aluminium extrusion length of, let's say, 1000 mm, would the length of the carbon rods be 940 mm?
Any ideas?

Most information I was able to find was the arms are 80% the length of the horizontal structure.  I did find a copy of the original Google Sheets that everyone used a few years ago here.  The source of that link did mention that there may have been some issues with it but all of those links were dead ends.
Some things to note:
The height doesn't matter, it has no relationship with the arms other than you are losing approximately the arm length from the height when figuring print area as some arms will approach vertical when reaching the outsides of your print area.
The arm length isn't terribly important from what I could find.  Longer arms = less travel of the carriages and possibly lower resolution.  Shorter arms = more travel of the carriages and possibly lower print speed due to required movement.

The link seems to go to a spreadsheet that doesn't have any formulae in it. However, I managed to find a copy, from Google groups: How to calculate Delta Dimensions for new build

Do you happen to have the source of your link? I would be interested to read it.

To compliment tjb1's answer, The link seems to go to a spreadsheet that doesn't have any formulae in it. However, I managed to find a copy, from Google groups: How to calculate Delta Dimensions for new build.
However, another source of the Document is Kossel frame calculator (delt...@googlegroups.com). Right at the top is a posting of Johan's (who is the designer of the Kossel) spreadsheet, which is essentially the same as before, but it is contained within an interesting message thread.
There are a few more calculators, that a quick google search will throw up, which I have listed in a short blog, Kossel - The Ratio:

Delta Frame Calculator | OpenBuilds

KosselPrinter/Kossel frame calculator.xlsx at master · aleung … – GitHub

Kossel frame calculator – Google Groups

Calculations | Pearltrees

I have an enhanced version that allows additional parameters to be modified, see Github: Greenonline/Kossel/Spreadsheets.

Design Process by David Crocker
Apparently, the ratio is not particularly vital. I found a design process in the comments section of More upgrades to the large Delta 3D printer:

The design process goes something like this:

Estimate the size of effector you will need.
Given that effector size, work out how close to the towers the nozzle will be able to get. From that and the desired printing radius,
work out what radius the towers are on.
That fixes the lengths of the horizontal extrusions. Choose the diagonal rod length so that when at the edge of the bed opposite a
tower, the rods to that tower are at 20 degrees or a little more to
the horizontal.
Given that diagonal rod length, choose the rod separation. I suggest about 1/6 of the rod length (this is larger than on my delta).
If that rod separation means you need a larger effector, repeat from step 1.
Choose the tower height to give the required print height at the edges of the bed, when one pair of rods may be more or less vertical.

When I queried David about his use of the 0.8 ratio, again in the comments section, on Building a large delta 3D printer, this was his reply:

The notion that there is a single ratio of diagonal rod to horizontal
extrusion length that is right for all delta printers is misguided. It
depends on the geometry of the corners that join the horizontals to
the towers, the size of the effector, and the carriage design. What
matters is that the rods are at no less than 20 degrees (preferably 25
or more) to the horizontal when the nozzle is at the edge of the bed
opposite a tower.


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What does Marlin's G30 code do?
I'm using Marlin 1.1.0RC8 to control an MPCNC, using a RAMPS1.4. We've just added a touch-plate to do Z-probing, which works nicely for a single probe (I just want calibrated height for variant bit-lengths, not bed-leveling, but I think it amounts to the same thing). I've set it up in Marlin as FIX_MOUNTED_PROBE, which seems closest.
I can make it do a G38.2 Z-50, G92 Z12.6 (which sets Z to the height of the touch-plate, 12.6mm), which is ok to be going on with, but it seems I'm having to hard-code the Z offset, which I'm sure should really be set by eg Z_PROBE_OFFSET_FROM_EXTRUDER or M851.
My feeling was that I should be able to invoke a G-code G30, and it would do a nice fast-slow double tap, do the equivalent of a G92 Z+zzz to set that height and then withdraw to a safe height. And after a bit of config, it does exactly that...
... except it doesn't do anything with the height that it measured! Seems odd. The G30 code seems to be an elaborate way to move the head up by the clearance amount, via a touch-plate (with the added excitement of being able to crash the bed if anything goes wrong)! What's the point?
Have I misunderstood what G30 is meant to do? I've read the docs here, and traced through Marlin_main.cpp and there really is no "outcome". Unless I've missed something?

I note that I don't have end-stops on Z, so I can't home/G28 that axis. I can't see that it makes any difference, but I'll go through the code later and see if that's what's wrong.

I believe G30 is a carry-over from CNC (G-code originated for CNC not printers)
I believe it is for going to a secondary reference (home) position and includes an optional by-way-of address that can be included in the command.
Looking at Marlin 1.1.0-1 (latest release), it seems to do what you said:

Move to the requested position (if selected in command, else N/C)
Deploy probe
Go home
Stowe probe
Report the requested position and probed Z position
Report the current position (home?)

It appears that for Marlin, there is only one reference address (home); so, it would seem a G30 would be the same as a G28 (go to primary reference); but, not so.
It looks like G28 is a home of a different color.  It looks like it homes the axis one-at-a-time and does not support a by-way-of location.  Note that you can select which axis to home by adding the letters 'X' 'Y' and/or 'Z' to the command.
I am not sure what benefit this command has for a 3D Printer other than allowing you to alter the printer's path to home.
Note: Unfortunately I do not have Marlin code up and running on my printer now so I cannot confirm what I am seeing in the code.

Mark, I haven't forgotten you've written this! Your contrasting of G30 with G28 surprised me so much - I hadn't thought of G30 as a HOME variant - that it made me re-evaluate all my assumptions, and I'm waiting for a rainy weekend to sit down and properly update all my preconceptions! In particular, G30 does "report" the probe position (back to the monitoring app); I was expecting it to store it internally as a reference... will investigate further.

I’ve recently had a need to use Z-probe touch
plate on my MPCNC + Ramps 1.4 + Marlin 1.1.5 setup.
Thought I’d share what ended up working for me.
In Marlin Configuration.h, I made the changes to enable Z-probe:
#define USE_ZMIN_PLUG
#define Z_MIN_ENDSTOP_INVERTING     true
#define Z_MIN_PROBE_ENDSTOP_INVERTING   true
#define FIX_MOUNTED_PROBE
#define PROBE_DOUBLE_TOUCH
#define Z_MIN_POS -100

However, the following might be the key to your issue.
G30 did not do anything for me as well, until I changed
these values to 0.  The G30 now lowers Z until the Z probe
is triggered. I needed to send a G92 to set the new Z value.
Works like a champ!
#define X_PROBE_OFFSET_FROM_EXTRUDER 0
#define Y_PROBE_OFFSET_FROM_EXTRUDER 0

In case you’re interested, in ultralcd.cpp under
lcd_prepare_menu(), I added the a menu item to perform
the probe.  This way I don’t need a computer to setup
the machine and launch a gcode file from the sd card.
  #if HAS_BED_PROBE
        MENU_ITEM(gcode, MSG_PROBE_Z, PSTR("G30\nG92 Z19.05"));
  #endif

Hope this is helpful for you, even after a couple years late.

It is unclear which parameters are set to zero. If you mean the probe offset values, that is not a good idea. Note that this question deals with Marlin 1.1.0, in between 1.1.3 and 1.1.4, the G30 command has undergone a change.