Calibration Cube Issue - S3D

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atomic_peach
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Location: Philadelphia, PA

Re: Calibration Cube Issue - S3D

Post by atomic_peach » Sat Jan 14, 2017 4:43 am

I was going to create a new thread but I am having the exact same issue as Rara. Both the black PLA from MakerGear and the red PLA PRO (PLA+) from eSun have these gaps in the top and the bottom of the print.
IMG_20170113_210419.jpg
My cubes are measuring ~19.97 on one side and ~20.03 on the other, with height measuring just above or at 20. I printed one block at 0.2mm layer height and one at 0.1mm layer height in each color, but added more top and bottom layers with the red. The smaller squares in the back were testing extrusion multipliers (0.91 and 0.95). The 0.95 was puffier around the overlap but still has the same gap.

I am mostly perplexed by the gap only, but consistently, showing up every two threads. This, mixed with the varying (and also consistent) measurements on X and Y, make me think it is belt tension or firmware based. Could belt tension cause this (i.e. is it backlash error)? Could factory high acceleration settings be amplifying or causing the issue? Any incite is greatly appreciated.

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zemlin
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Re: Calibration Cube Issue - S3D

Post by zemlin » Sat Jan 14, 2017 5:12 am

My theory on different X and Y dimensions is nominal diameter differences of the timing belt sprockets on the stepper motors. I haven't done the math, but I believe minuscule diameter differences would easily manifest as scaling errors.

I've found my parts clean up a lot when I reduce perimeter and solid infill speeds. I run those 1000-1500mm/min, so if my default speed is 4800, I'll run those at 25%.

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Rara
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Re: Calibration Cube Issue - S3D

Post by Rara » Sun Jan 15, 2017 11:57 pm

I'm still not sure what is going on here, which you can translate to "I never solved the problem but just learned to accept it." Two brands of regular PLA, another 'enhanced' PLA, and then an old and a new roll of PET-G I tried all do it. Fussing with things seems to affect X/Y/Z dimensions but I can't get a good infill - I needed a solid part recently and all the little voids meant I couldn't get the strength out of it that I needed..grumble grumble..
2012 M2 V4-PTFE

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atomic_peach
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Re: Calibration Cube Issue - S3D

Post by atomic_peach » Mon Jan 16, 2017 2:49 am

Well I can confirm that slowing to 50% on perimeters and top/bottom infill did help, but 25% had issues with the perimeter/infill overlap and lost quality with no gain in top/bottom infill closing. It is still very apparent that two rows of filament are close followed by a gap. I swapped back to MG Black and saw the same problem again, so it is definitely not filament or speed based.

I will check belt tensions in the next few days. Is there any specific print I can run that helps check this?

ksevcik
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Re: Calibration Cube Issue - S3D

Post by ksevcik » Mon Jan 16, 2017 4:17 am

I think you have a backlash problem. The biggest symptom would be not round cylinders as seen here.. If you can make a model with a cylinder that's a little more than two extrusion widths in wall thickness, s3d will print it with two circles in opposite directions, like in that thread. If there isn't a consistent gap between them, you've got backlash. The problem axis is always perpendicular to the flat part of the circle.

Backlash can be from a loose belt, loose pulley on a stepper, loose hardware holding the belt clamp to the axis, or in that case, a belt that's loose in the belt clamp and needs to be shimmed.

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