The parts in the pictures were both sliced in Cura 3.4.1, one was printed on an Ender 3 and one on an Alfawise U20. Yesterday I had a friend print one on his CR10 that I sliced in Cura and all 3 have almost identical gaps in pretty close to the same places. He also sliced the part for me in S3D and the top surface came out perfect (but the side walls of the holes weren't any where near as good as Cura). I sliced another one in Ideamaker and while it had problems elsewhere, the top layer was fine.
With the above in mind it seems unlikely that it's a backlash/play issue, but I will check to make sure.
I really want to use Cura, with the exception of the top layer it's producing the best parts and in the fastest times. It's ability to hide the Z axis hop makes me very happy. I also find it very easy to work with. But the top layer issue is killing it for me. It doesn't do it on everything I design, but where I have holes near straight walls it does it most of the time.
I will try your suggestions, I've increased flow to 105% (110 was way too much) and I've increased the skin overlap, that produced the parts in the pictures, by far the best I've gotten. And no, it's really not that bad, but I don't want it there at all if possible. Tomorrow I'll try your suggestions about line and wall widths and see if that helps.
Thanks very much for responding!
Edited by 3rdpig
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gr5 2,224
Well the fact that it is not symmetrical means that part of the problem is backlash/play. Most likely only in one axis (X or Y but probably not both). With power off try pushing the nozzle around and see if it moves before the stepper moves. Usually play is caused because the belts are loose or the friction is very high. On an Ultimaker style gantry, put the print head in a corner and pluck the belts and they should be around 100Hz.
But that is not the primary problem. The primary problem is probably underextrusion although it doesn't look that bad. Are you using Cura? Make sure you explicitly set all the line widths the same and to a value equal or only a little smaller than the nozzle width and make sure the wall width is an integer of the line widths. For example if the shell width is 0.35mm the wall width could be 0.7mm but not 0.8 or 0.6mm (which could cause this issue seen here).
As a quick fix also try increasing the skin overlap. But if the inner most shell is messed up (say it's set to 0.1mm) then you reall need to fix that instead.
Another quick fix is to drop the speed by 25% and increase the flow by 25%. But this is not a great idea.
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