Nozzle scraping top of tall prints
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This has been bugging me for a while but I never did figure out why it is doing this.
I print with a 0.2mm layer height with a Juiblee printer and PrusaSlicer although this problem seems to be completely independent of the printer or the software used. The taller the print the more this seems to be an issue.
I am currently at 75mm height and it sounds like the nozzle will rip the print off the build plate any moment now. I am printing a pipe elbow with a 70 mm diameter.
Part of why it sounds so horrid is that the print has tall walls so if the nozzle touches the walls, the wall vibrates and amplifies the noise.
I have probably had this issue from day one but I am wondering if anyone has ever looked at exactly why this is happening. I am assuming that distortion of the print from cooling is the issue but don't understand how this is possible if the printer puts down a layer 0.2 mm above the existing wall. Sure, the wall could distort but wouldn't that distortion be compensated for by the mere fact that the nozzle is 0.2mm above the existing print? How can the nozzle touch the print itself? The only way I can see this happening is if the existing print distorts more than the 0.2mm of the layer height.
There is one other possible way one might be able to explain this phenomena and that would be if the layer being put down adheres to the print puts enough sideway load on the existing print that the wall vibrates.
The issue does seem more pronounced with travel moves that are crossing the object. I do not use z hop.If anyone can offer an explanation of the mechanics of this issue so I can understand it, I would appreciate hearing about it.
PS.:
yes I can turn on Z hop but I am at around 5 hours in a 7 hour print
'avoid crossing the print' is enabled in PrusaSlicer -
@jens55 several options here:
a) overextrusion but I'd assume you would have done flow calibration
b) bed pulsing when not PID tuned
c) die swell from printing too fast (with cold core extrusion as a side dish)
d) similar, filament expanded by trapped water escaping
e) material buildup on the nozzleand the favorite: any possible combination of the above.
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@oliof, thanks for your thoughts. They are all good points but considering that this happens on multiple printers makes it highly unlikely that the issue is with any/all printers.
It is interesting to note that my print that was sounding like it would be ripped off the build plate finished without issues. Also, once the print closed up on the top with the walls of the fitting coming together, there were no more scraping sounds.
I will try to remember to enable z hop on prints that have tall flat features without proper sideway support.Anyone else run into this?
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@jens55 My best guess is overextension caused by the slicer. Many years ago, when I first started with 3D printing, I had similar problems. I came across a video by someone (can't remember who) who did a very scientific study printing multiple parts with varying extrusion multipliers and checking all of those parts for dimensional accuracy, finish, and weight. His conclusion was that 3D prints are very tollerant of under extrusion but extremely intolerant of over extrusion. IIRC, even parts that were printed with 80% extrusion multiplier were fairly acceptable in appearance and dimensional accuracy but anything over 100% was pretty awful. Ever since then, I've always used an extrusion multiplier of 90 to 95%.
Now of course, this might only be specific to one slicer and not all slicers but I think it comes down to how well the slicer handles die swell. But it's easy enough to try with an extrusion multiplier of (say) 95 % and see if that helps.
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@deckingman to support your point with a mechanically sound extruder design where I don't need to calibrate esteps since it's industrially manufactured, my flow rates have been anywhere between 85% and 95%; usually 93%. On textured PEI, I add one or two percent for the first layer. This is across multiple slicers (Cura/PrusaSlicer/SuperSlicer), with RRF, Marlin, Klipper alike.
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@oliof said in Nozzle scraping top of tall prints:
@deckingman to support your point with a mechanically sound extruder design where I don't need to calibrate esteps since it's industrially manufactured, my flow rates have been anywhere between 85% and 95%; usually 93%. On textured PEI, I add one or two percent for the first layer. This is across multiple slicers (Cura/PrusaSlicer/SuperSlicer), with RRF, Marlin, Klipper alike.
Useful to know - I've only ever used Slic3R and variants thereof. But I've used E3D Titan extruders, Bondtech BMG and more recently Bondtech LGX and all of these with various hot ends and nozzle sizes. I've always ended up using extrusion multiplier between 90 and 95% despite calibrating said extruders. I guess a useful exercise would be to see if nozzle size plays a part. If my conjecture about die swell compensation is correct, then one would expect less over extrusion as the nozzle diameter approaches the filament diameter. I might try that with some larger nozzles when I get time.............
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@deckingman I haven't seen differences in a range between 0.4 and 2.0 nozzles in this regard (> 0.8 was on an Ultimaker Original+ so with 2.85mm filament, with the 3dsolex Matchless Race nozzles that predate CHT), but I haven't done methodical research either.
What did change tho was PA and retract, massively.
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I will add a 2 cents comments here: never underestimate the Z axis calibration, I had your problems before and was just a matter of calibration on my Z axis (Im a fan of 0.1 and below layers jaja).
Also I will vote a +10 on the overestrusion and here I have something I looked somehow deep: the teeths of the hobbed bolts on the extruders, even the teehts on the bondtech dual geared extruders can have a huge impact on extrusion, to a point where changing them to a smaller size can give you upto 4% difference on the extrusion rate. Even on diferente material you can find a difference: softer material suffer more on this that harder materials. And even speed changes extrusion sice teehts tend to "bite" more deeper if you print faster.
