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Troubleshooting odd shape cube

Posted by Turtle_Cat 
Troubleshooting odd shape cube
June 09, 2018 12:25PM

Just built a new delta printer and I'm putting her through her paces, noticed this issue.

Ignoring the other coast/wipe/pressure issues on the corners, I've never seen this error before. The bottom corner of the print is sort of curved, always in the same direction, toward the Y tower. The error evens out over time, so it's only the first dozen or so layers that follow this pattern. It happens regardless of orientation. At first, I thought it was nozzle tilt because my effector had an issue, but even after fixing that the error remains exactly the same.

I'm using a duet and getting about .038 deviation after autocalibrating, so I would think that I'm close enough to be getting correctly shaped objects. If anyone can point me in the right direction it would be greatly appreciated.
Re: Troubleshooting odd shape cube
June 09, 2018 11:34PM
Sorry, I can 't help you directly. But maybe what you're seeing is a version of a problem I'm trying to fix on my delta. For me, the output is distorted... in the Y direction the dimension is perfect, but in the direction opposite the X tower (i.e. at 30 degrees to the X-axis) it only 95%. I'd thought I could correct this by scaling up by 5% in the X axis and rotating 30 degrees, which ought to get the dimensions accurate. But another consequence of the error is that there's 5% over-extrusion in that direction.

There also seem to be some Z-axis errors due to geometry, which seem to be in bands.

So I'm hoping, firstly, that the above gives you some insight that'll help you, and secondly that someone will give you an insight that helps both of us.

Re: Troubleshooting odd shape cube
June 10, 2018 02:16AM
The only other case I've seen of an issue varying with height like that on a delta printer was caused by using steel cored belts. After a while the cores fractured over a length of the belt, because the pulley radius was too small for the steel cores.

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Troubleshooting odd shape cube
June 10, 2018 09:05AM
I'm definitely just using regular fiberglass belt, but I did have some tracking issues early on where my motor mounts tilted and caused the belt to run hard up against the flange of the pulley and idler. I'll take another look at them, thanks.
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