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Strange distortion when printing an arch

Posted by jamesd256 
Strange distortion when printing an arch
August 07, 2016 06:14AM

I have a Sumpod Basic, which is based on ramps 1.4. I am using Marlin currently.

My calibration cube comes out nearly perfect, but when I try to print a linear bearing mount I designed in Sketchup, I am seeing weirdness printing the arch shape. It seems that one axis is getting stretched. I tried rotating the z-axis 90 degrees, which reversed the problem. Switching the x and y stepper drivers does not influence the issue.

On one side, the straight side of the arch is too narrow (2.7 instead of 3mm) and on the other side it is too wide at 3.3mm, and actually splitting vertically.

The problem has only shown up on this part, as I have designed and printed a few other parts which came out perfectly.

Has anyone come across this one.

Re: Strange distortion when printing an arch
August 07, 2016 07:42AM
Have you checked the gcode before printing? What program did you use to slice- it should show a preview of the gcode, or you can type gcode.ws into your browser's URL locator, and load the gcode file. If it looks normal you have a printer problem. If not, it is probably a Sketchup problem.

From the looks of the print, the extruder is grossly over extruding. Have you calibrated the printer? If the acceleration and/or jerk are set too high it can cause layer shifting.

Sketchup is poor software to design objects for 3D printing. There is another freebie CAD program with a similar user interface to Sketchup that works much better and does much more- Designspark Mechanical. You won't have to repair the STL files it produces before you can print them.

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Strange distortion when printing an arch
August 08, 2016 07:35AM
Possibly play in one of the drive mechanisms. This would happen if it always printed in the same path direction (clockwise for instance). So when it moves left it doesn't go far enough left and when it goes right it doesn't go far enough right. If you print fast so there is inertia it can tend to be too far instead of too little.
Re: Strange distortion when printing an arch
August 15, 2016 07:54AM
Thanks for the replies.

It definitely wasn't layer shift - had my fair share of that, but gone after scrapping the cheap stepper motor drivers the printer came with.

It was due to some play in the rack gear. I should have remembered from last time this happened (haven't touched the printer for a couple of years).

I have to say in defense of sketchup, I used to get into trouble with it a lot, and spent a fair while trying to fix models, but now know how to take my time and when to scrap a model that's gone wrong, and as a result don't really have problems with getting good STL out of it.

The link for checking the STL is very useful, but perhaps duplicates some of the problem detection in Repetier host?

I am grateful for the heads up about Designspark Mechanical - a wonderful tool I didn't know about, which also brought me to finding FreeCad and learning more about OpenScad.

After spending a fair while learning the pros and cons of each of the above, I have concluded that there are jobs that each tool is best for, including Sketchup.
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