[Feature Request] Improve wall start/stop pathing to prevent zits and blobs

[Eisenmeower 0]

I'm having issues with outer wall zits on my CR10 when printing at high speeds and I feel like I've tried everything resolve it. I believe that the problem lies in how Cura handles pathing at wall changes. Not every model has good corner to hide a wall seam.

 

I have no coding experience but I've attached an image to help illustrate my solution.
I've enabled "Optimize wall printing order" and "coasting" which makes things easier to see.

 

Fig 1. This is how Cura currently handles inner to outer wall moves. The nozzle moves to the end of the path and makes a hard 90 deg turn to reach the start of the next wall. I've also noticed that Cura treats this tiny move as a travel. In my case, travels are set to 160mm/s. I believe this fast sharp turn is what causes the zits and is exacerbated by higher travel, jerk, and acceleration speeds required to print quickly. It's further exacerbated with "optimize wall printing order" turned on because the zits stack up.

 

Fig 2. My proposed solution with coasting enabled: Instead of the sharp angle travel at the end of wall 1, run a coasting (NOT travel) path directly to the start of the next wall. This would greatly reduce the sharp angle and resulting vibrations at the start of the outer wall, especially with the currently available option to reduce the coasting speed. Finally, at the end of the outer wall path, follow a shallow angle back to the inner wall to prevent visible bulge at the end of the path before travel or retraction

 

Fig 3. An example of this method without coasting volume. Offset the start/stop points of the inner walls based on the desired placement of the outer wall seam (if using seam alignment that prefers corners). This still allows for a non-extrusion coasting move that takes a shallow angle path to the start of the next wall. End the outer wall path with a shallow angle coast back into the inner wall before traveling.

 

 

[gr5 2,170]

It's not the travel *speed*.  This travel distance is tiny - maybe 0.4mm, right?  It takes more like a cm to get up to 160mm/sec depending on your acceleration.  Acceleration for CR10 is incredibly slow because it moves the whole bed.  Probably around 500mm/sec/sec (versus ultimaker which is 5000 to 9000 mm/sec/sec).  So I'd be surprised if the speed gets up to 20mm/sec.  It could be the jerk speed.

 

Still this is a cool idea.  You could easily remove (by hand editing) that one point at the start of the travel and it would just skip that spot and move diagonally and you could see if that fixes it.

 

I recommend downloading and installing "repetier host".  It's free.  It has a tab on the right screen that lets you examine the gcode on the right side and see the part on the left side.  You can go to the layer you care about and click on the gcodes and it highlights the gcode moves in yellow on the left side.  You can click and drag a large selection of gcodes to "find your way".

 

Then you can see exactly which gcode is for which move and delete the one in question to see if it makes any difference.  You'd probably want to create a small custom part to show the problem and that can print in just 5 minutes so you can experiment to see if this makes things any better.

 

I think you will have better luck just slowing down the print.  On the CR10 I think there is a TUNE menu while printing - you could try printing at 1/3 speed to see if a few layers get better and then play with what speed is fastest but still hides the bumps.

 

[yellowshark 153]

Hi I had a similar problem last week. I was printing circular geometry, reasonably unusual for me. I fixed it by changing two settings - no stupidly I do not know whether they both contributed or just one of them! I will revisit that but I was in a rush at the time.

 

I changed z-alignment from random (which I always use) to user specified and changed print acceleration from 3000 (default) to 1500.