Travel - Retract at layer change.

[j_keiter 0]

When I look at gcode it appears the layer change(move in Z) occurs before the retraction.  FYI Z moves are relative mode.
G0 F600 X143.508 Y149.923 Z0.8
;TIME_ELAPSED:18.152899
;LAYER:1
G1 F4800 E-6
;TYPE:WALL-INNER
G1 F4800 E6

Since my printer has a very slow Z move, I'm getting a blob as Z moves to next layer.  I want retraction to occur before Z move not after.  

 

Thx Jason

[burtoogle 516]

No, that's not how current Cura is coded. It does the retraction before the z change.

 

What version of Cura are you using?

 

Could you please provide a complete gcode file rather than just a snipped. Thanks.

[j_keiter 0]

Complete Gcode file attached.  LAYER:5 LAYER:9 LAYER:19 and possibly more do retraction after z move.  Other layers are correct.

;FLAVOR:RepRap
;Generated with Cura_SteamEngine 4.6.1

Arm.gcode

[burtoogle 516]

Thanks a lot for the the gcode file, I can see where it's not retracting and that doesn't look right. Could you also please provide a project file for that print? Do File->Save and attach the .3mf file to this thread. Thanks.

[burtoogle 516]

Ah, I think I know what the problem could be, looking at the gcode for the missing retraction just before LAYER:5, the distance travelled is less than the value of retraction minimum travel so the retraction doesn't occur. A workaround would be to reduce the value of that setting.

Could you still please provide the project file, thanks.

[burtoogle 516]

The UM devs changed the behaviour fairly recently so that Cura never generates a retraction when the travel distance is less than the minimum travel distance setting. This is true even when retract on layer change is set. Maybe there is a case for allowing the retraction in that situation to help with the slow z change.

[j_keiter 0]

Burtoogle, you are correct.  The 'Retraction Minimum Travel setting at 6mm was preventing the retraction from occurring prior to z move.  I reduced to 2mm and Layer 5 was now correct but Layer 9 was still wrong since it had an even smaller travel move than 2mm.  "Maybe there is a case for allowing the retraction in that situation to help with the slow z change."   You nailed it.  Wish I knew how to do this.  .3mf file attached.  

arm.3mf

[burtoogle 516]

I don't think there's anything you can do to alter the behaviour. I have modified the slicer so that it will force the retraction to

occur on that last travel move and sliced your project, I attach the gcode, could you please print it and let me know if it is good. If so, I will submit my changes for the UM devs to include in a future release (if they approve).

 

CFFFP_arm.gcode

[j_keiter 0]

I'm still getting a big blob as shown in pics attached.  I still think you should ask developers to make change to allow retraction before z move.  Sadly I must have some other issues that prevent me from giving you proof of fix.  Sorry!

[gr5 2,270]

Lowering the print speed will help a bit with those bumps in the photo.  Also make all the print speeds the same speed (I think there are 7 printing speeds) but keep the travel speed fast.

 

More important than the printer's Z speed is the Z acceleration.  I read a good article about increasing Z accel for my old printer and it really helped a lot.  I kept increasing accel until it would skip and then I backed off by about 50%.  now Z changes are so fast it's like a "click".

 

 

[j_keiter 0]

My print speed was too high based on www.printitindustries.com/pages/print-speed-calculator.  Travel is 120mm/s.  I already had increased Z acceleration and increased Z jerk to just tolerable.  Retraction was and is scary fast.   Still not printing very well but it appears the blob on sidewall is gone.  It appears the retraction after z move was not an issue after all.  I still think cura should fix though.  

[burtoogle 516]

6 hours ago, j_keiter said:

I still think cura should fix though.  

 

 

I have submitted a fix to the Cura devs and they will decide whether to incorporate it or not.