Thinning extrusion problem - cause?

[dorgeman]

thinning of walls extrusion over print

Can someone tell me what causes the problem shown in the picture? I have tried to print this object about 100 times now - all with approximately the same issue. The three perimeter walls become thinner and thinner as the object builds upwards, leading to either complete failure of the print, or an exceptionally weak object.

It does not appear to be a problem with the extrusion rate - although it looks like it. I can print a single wall cube of arbitrary size and the wall thickness will match the configured thickness. I can print a three perimeter, hollow cube (no top, bottom, or infill) and the three perimeters will print together like a single solid wall. I can do that with a larger cube so that the amount printed is closer to this model, and there is still no issue. If this is a problem with extrusions steps, I don't think any of those tests should have printed properly.

It does not appear to be a problem with retraction. I have tried many variations tweaking retract settings. My theory was that the biggest difference between this model and test cubes is the large amount of retract that takes place. After failing with many settings, I turned retract entirely off. The print was a wreck because of no retract - but it still showed the same thinning of the perimeter walls.

I have tried many different temperatures, all with the same results.

I am getting very frustrated with this, and have run out of ideas on what to try. Has anyone seen anything like this? Any ideas of what causes it and what the fix might be?


-David

[Tesse]

Hi dorgeman,

could you post the factory file or your settings?

Tesse

[dorgeman]

Robot_Maker_Faire_65pc-8.factory

(1.13 MiB) Downloaded 246 times

Here is a factory file for the most recent failed settings.

[Tesse]

try setting the extrusion width to auto or decrease it to about 1.2*nozzle dia (0.48mm for .4 nozzle) under the extruder tab.
ref:

• viewtopic.php?f=8&t=2232
• viewtopic.php?f=9&t=2292

Tesse

[dkightley]

I concur......and you're not extruding enough plastic. Increase the extrusion multiplier.

See also here: https://www.simplify3d.com/support/prin ... gh-plastic

[dorgeman]

I set the extrusion width to auto. That made no difference. It really shouldn't since the manual width was not much higher than the auto value, but figured it was worth a shot anyway.

I also thought maybe the cooling - as slight as it is - was causing a problem. I know that the upper parts of this model would fail without some cooling, but I turned it completely off to see if that was a contributing factor. Turning cooling off made no difference.

Increasing the extrusion factor isn't likely to be an answer. The current extrusion multiplier gives a correct (possibly even slightly on the high side) width and makes the walls correctly for parts with straight walls. Also, the solid layers on the bottom print without any gaps at all (for this model and for test cubes). If I do an object that has a solid top - like a test cube - the same thing - perfect solid top with no gaps. The multiplier used to be 1.0, and created an obvious overextrusion where the nozzle dragged through the already printed lines and had to push filament out of its way. All of that points to the multiplier being correct. I concede that it sure looks like simple underextrusion, but I think there is something more complicated happening here.

I had thought at one point that I must be losing steps in the extruder once it runs for a while - but again, it works perfectly for other objects. I cannot come up with an explanation for why the extruder would have issues with skipping steps for this model but not for others that are just as large. There is no debris in the MK8 extruder gear that indicates any stripping.

I had also thought at one point that maybe it was related to using custom supports, but I have done it with default support and also with no support and get the same result.

I had thought that maybe it was the temperature as well (I normally print a lot hotter for ABS). I thought that since this model has a lot of small segments and curves that XY never would get to full speed, and that maybe enough filament was oozing out during some of that slower motion to starve the nozzle, but lower temperatures didn't make any difference either.

[dkightley]

Compare your part with the pink coloured part in the photo in the quality guide I attached a link in my last post.

Do they look similar??? I think Yes! Therefore I suggest you take the advice of the professionals who wrote the guide....increase the value of the extrusion multiplier, as I assume you have the correct filament diameter set.

And increasing temperature will allow plastic to be extruded more easily......so raising the temperature may help.....but I have no idea of what to, as I print exclusively in PLA.

[Tesse]

i totally agree with dkightley!

I would measure the correct fillament diameter and set it under the other tab. Then i would get rid of the horizontal size compensation on the same tab: set it to 0. makes no sense on such a design object.

And level your bed. I see that you have set an offset. Maybe the first layers get squashed and therefore look good. The higher your print build up, the less this effect will help joining your perimeters.

Set the width to auto or 0.48mm at the moment and play with the extrusion multiplier. make sure that your extruder is calibrated.

I don't use a fan at ABS prints at all.

This are just some guesses. Maybe it helps.

Tesse