Nozzle still extruding PLA during cool head lift

[chenobble 1]

I've been getting problems with excess material on my UM2 prints recently so I paid extra attention during my latest run and noticed that during the 'Cool Head Lift' period the nozzle is continuing to extrude PLA at a steady rate.

When it goes back to the print this coil of half-cooled plastic is still hanging from the nozzle and either sticks to the side or, worse, is mushed into the next layer leaving huge lumps of unwanted plastic on the final print.

Is this something I can fix with the settings or is it a hardware issue?

[Running Ultimaker Silver PLA on my stock UM2]

[danilius 118]

I have had quite a few issues with the cool head lift, so instead I print a wipe tower or a few copies of the same thing. That way I usually get one decent print. I have found that cool head life always results in goo everywhere, even with longer retraction.

[Dim3nsioneer 557]

Increase retract distance and retract speed on the UM2. Make sure the filament is not broken inside the Bowden tube.

[chenobble 1]

danilius - the wipe tower is a good idea and making it something small but tall wouldn't eat into my print time too much. Will definitely do this next time.

dim3 - i'm not convinced retracting it further or faster will help as the material would still be there. I'll check the filament tonight. Cheers!

[IRobertI 520]

Is it actually retracting? Sounds like you're getting a lot of oozage here, more than I would expect. But that might just be me reading more into the text than I should.

Might also want to consider lowering temperature and increasing travel speed to help minimize the problem.

Personally I never use cool head lift.

[danilius 118]

 

@IRobertI, I get that oozing with the cool head lift. It's why I generally do not use it anymore, unless it's going to hand around for a second or so. Much longer than that the ooze becomes quite serious. Same if I place two parts really far apart on the bed, there will be some ooze deposited on the landing site, but it comes off easily after the print.

[IRobertI 520]

Ah, never mind me, for some reason I was thinking about the z-lift during retraction/moves, not cool head lift.

Yeah, cool head lift will cause quite a bit of ooze since it can be sitting around for a "long" time before starting to print again. You can't fully empty the nozzle as it's waiting, so it will ooze no matter what you do really. The purpose of the retraction is more about relieving pressure than emptying the nozzle so it works well for fast moves but when it's just sitting idle, well, it oozes.

Much better to print multiples or towers as already mentioned IMHO.

[gr5 2,172]

I've seen the same thing. It might be caused by the PLA slowly expanding as it heats up. Or it could be trapped air that heats up and pushes out a small amount. I found that these strings that are created from "cool head lift" are easier to remove than most. But having a second tower is my preferred method of dealing with this kind of thing.