G4 (dwell) causing stuttering motion on delta printer

screwtop

Hi, I'm trying to improve my printer's behaviour when restarting after retractions. It's a delta with Bowden and the filament takes a bit of time to start flowing properly again after a retraction. I'm using Slic3r and have tried to fix this using the "Extra length on restart" retraction setting, but with limited success. It seems that part of the problem is the delay time, not just the backlash in the Bowden setup. So, I'm trying post-processing the G-code to add a short dwell (e.g. G4 P100) after each forward feed of the extruder axis alone.

It's helping, but the printer seems to be doing several stops and starts when these dwells occur, rather than a single pause, resulting in a stuttering motion. It seems to do this even within a linear move, which makes me think it's something to do with the delta motion processing. With a long dwell time (say 1 s), the stuttering motion does not occur.

Here's a G-code fragment of the retraction, both before:

G1 X-71.531 Y-12.073 F2880.000 E81.43661

G1 F3600.000 E81.34661

G92 E0

G1 X-55.787 Y-16.250 F3600.000

G1 E1.80000 F3600.000

G1 X-39.750 Y-16.250 E2.82098 F1080.000

...and after:

G1 X-71.531 Y-12.073 F2880.000 E81.43661

G1 F3600.000 E81.34661

G92 E0

G1 X-55.787 Y-16.250 F3600.000

G1 E1.80000 F3600.000

G4 P100

G1 X-39.750 Y-16.250 E2.82098 F1080.000

Thanks for any help or suggestions!

Repetier

G4 is bad for deltas. It waits for all moves to finish and then does the wait. This means the move buffer is empty and we start with empty buffer. You might have noticed that a longer move from idle state also has this stopping in between. Same reason and that goes away when buffer is full. So not use G4 if you do not want this extra interruption. Also we have a wait move available it is not controllable by gcode. That would have allowed adding a wait in the move without loosing the buffer. But with available tools I see no good way. You would need to add slow moves but since you do not know where you are and what follows that is also bad. Maybe undoing retraction a bit slower would help to gain the time.

screwtop

Ah, I see - that's useful info about the planning. Slowing the retraction undo is an excellent idea - I've tested that and it is looking promising, and I think should give smoother restarting than my original dwell approach. Thanks for your help!