Specific part printing error.

[qholmes 0]

I have a small part that is giving me errors on one corner. The other corners are fine. its an L shaped part. It seemed to start when i was refining the design to make it fit the proper print width and height. Also to reduce print time and materials and create a better fit with another part. I had reduced the top ridge to 1.2mm thick. 

No matter where i place the part it prints the same. If i rotate it then the problem goes away but the edge of the part has some abnormalities in it. So i printed some tube type shapes to try and replicate it. both with round and straight corners. all printed perfectly. I recently changed the top ridge to be 1.6mm thick and the problem vanished. 

In the slicer it looks fine when you go through the layers. I was using Cura version 3.5 but did just upgrade to 3.6. But i get the error in both versions. I did notice that 3.5 gave what seemed to be a better more continuous path for the printer in the upper edges of my part. 

 

I print a group of parts together and this one is the only one that does this. multiple copies in the same job all doing the exact same thing.

 

Thoughts?

 

Thanks

 

Q

[gr5 2,268]

My first thought is that if you turn off jerk and acceleration control and if you print slow (e.g. 25mm/sec) this will go away.

 

I believe people call this the "Z seam".  In the old days some slicers printed the outer layer last and at the end it changes layers and if your Z acceleration is low it would overextrude and make a bump there which would be a vertical seam/bump.

 

Cura changes Z on an internal layer to fix this but the outer shell has to start and end somewhere before moving to the interior of the part.  This is *still* called the "z seam".  There are z seam options in cura to move the location.  A well tuned printer shouldn't create a z seam - or certainly if you print slowly.

 

Basically you want to crank up the acceleration and jerk values on your printer and lower the print speeds such that the head never slows down.  Any time the head slows down and you still have pressure in the nozzle you get a little overextrusion which causes these bumps.

 

Printing the outer shell before inner shell may help also (that's not default so you have to change that in cura).

 

[gr5 2,268]

Another solution is to plan for the Z seam and change the part in CAD so that it is cut off on the corner.

[qholmes 0]

I am not sure this is a Z bump..i have that on other things where you get a bump out along the entire z edge.. its annoying but i try to compensate for it and now that i know what it is called maybe i can work on fixing it. 

 

This looks like layer shift or i dont know what.. 

 

But my test prints that are the exact same thickness do not do this and also adding 0.4mm to the width also takes it away. 

 

Q

Edited April 30, 2020 by qholmes

[qholmes 0]

So i fixed this by redesigning the part to allow for a different print path. I think it was an anomaly in how it was generating the g-code.  

Q