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Corners not square?

Posted by MarkM_NJ 
Corners not square?
March 02, 2017 10:06PM
Hi everyone!
I'm printing a 20mm x 20mm calibration cube. What would cause the corners to bulge out? Attached is a crude example. I'm using a e3d v6 clone, 1000 acceleration, 15 jerk (did try other settings). Using slicer via repetier host.

open | download - cube_corner.jpg (31.6 KB)
Re: Corners not square?
March 03, 2017 08:06AM
Can you get a closeup photo of the actual print? Bulging corners are fairly common, and it's usually just a result of having to slow down to change direction. The pressure in the nozzle lags behind the commanded change in speed, so as the head slows down for the corner you get an excess of plastic which causes a bulge. The most direct way to reducing the problem is to increase the XY acceleration and jerk settings, but doing so will likely increase other problems such as ringing and missed steps. It's always a tradeoff.

Edit: If you're making your own designs, this is why you use a fillet on corners whenever possible, so as to maintain constant head speed as much as possible.

Edited 1 time(s). Last edit at 03/03/2017 08:08AM by JamesK.
Re: Corners not square?
March 03, 2017 11:30AM
Thanks for the reply James,
Here's a photo..
open | download - IMG_5567.JPG (357.8 KB)
Re: Corners not square?
March 03, 2017 11:45AM
OK, yes, that looks very typical. Try working your way up the jerk and acceleration settings until you see an improvement or run into the other problems. You may need a more complex shape to be able to see the trade-off between corners and ringing - something with a hole in the side often works well to show ringing. Acceleration in the 6000 to 9000 region may be possible if the machine is rigid and the print head light. I'm not sure what a high value of jerk would be - I don't like the noise and vibration so I run my machine with low jerk and acceleration, and design with a lot of fillets.
Re: Corners not square?
March 03, 2017 01:36PM
Thanks James, I'll try that.
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