Blobs of plastic while printing

[tom10122]

I get blobs of plastic when printing , it happens after The filament retracts and it starts to put more out.

[Polygonhell]

It can happen if you're printing too slow, but it's more likely that you are trying to retract too fast and losing steps. Mark the gear with a black pen and watch when it retracts to verify it is returning to the same location.

[tom10122]

John thought I was printing slow , 1500mm/m ? It may be retracting and skipping steps is retracts at 3000mm/m

[Polygonhell]

3000mm/minute is 50mm/s IME that's way to fast for a retract, and it's probably stalling, but verify by marking the gear and watching it.
I'd start with retracts at about 15mm/s (900mm/m) and work up from there.

1500mm/m is about 25mm/s that's actually not miles off where most people run for perimeters, I run between 10mm/s and 50mm/s for perimeters, depending on how accurate I want the part and how impatient I am, you can run sparse infill a lot faster, and rapid speeds can be in the 100mm/s+ (6000mm/m+) range.

IME speeds above a certain point don't make very much difference to run time, it get's dominated by cooling for small layers and acceleration at some point.

[tom10122]

Okay thanks I'll try it, Is it just me or does PLA stop sticking the kapton after a few prints? Doesn't seem to stick easy anymore. I ussually use 3m blue painters tape but i dont know where my role went

[tom10122]

didn't seem to work but I got almost all of it to go away by using 0 lift so no blob could possibly form

[Polygonhell]

Can you post some images of the blobs, it might be easier to see what's forming them.
If you think it's the retract, you can disable it and see if it goes away.

[johnoly99]

Hey Polygon, I run 55mm/sec retract speeds. Our extruder has that massive gear ratio on it, so we have to retract fast to get any sort of speed on the filament to combat oozeage. You're right though, if it was a direct drive or wades style extruder, 30 is a more safe speed. We don't have near the torque needed with that gearing, so we can run that fast without skipping no probs.

[tom10122]

no blobs with 0 height on retraction, just found out that my z axis was off so I need to calibrate it again

[Polygonhell]

Hey Polygon, I run 55mm/sec retract speeds. Our extruder has that massive gear ratio on it, so we have to retract fast to get any sort of speed on the filament to combat oozeage. You're right though, if it was a direct drive or wades style extruder, 30 is a more safe speed. We don't have near the torque needed with that gearing, so we can run that fast without skipping no probs.

I can't run near that retract speed on my original H1.
Some of that is because there is almost no "hobbing" on the feed roller and to get a consistent feed it needs to be excessively tight, so when it retracts it stalls. This might have changed with later kits, I keep meaning to take mine apart and actually score the roller, but I never seem to get to it.
If as he says he gets no blob when retraction is disabled, then then the likely cause is stalling on retract.
He can confirm that by marking one of the faster moving gears and watching it to see if it does indeed return to the same spot after a retract.
Without a mark on the roller or a gear it can be really hard to see and the extruder can appear to be functioning correctly.

Since he's using Mach he could also just have the acceleration for the extruder set too high causing the stall on the fast reverse.