Bubbles (Hickup) in cylindrical Prints
Hi Guys
Does somebody know the issue attached in the pictures above?
It is like bubbles on the outer-line of cylindrical pieces. How can I solve this?
I use a MK3S. The most often it appears with BioFusion-Filament.
Thanks in advance
RE: Bubbles (Hickup) in cylindrical Prints
Look like seam marks.
RE: Bubbles (Hickup) in cylindrical Prints
@lichtjaeger
Is that filament related or printer related?
So, can I improve this? ^^
RE: Bubbles (Hickup) in cylindrical Prints
I think this video explains it the best:
Must be this thing I've had. That means it is hard (impossible?) to eliminate.
RE: Bubbles (Hickup) in cylindrical Prints
[...] Must be this thing I've had. That means it is hard (impossible?) to eliminate.
With current consumer-grade FFF printing, sadly, that is true. Each layer has to start and stop somewhere, so you wind up with a seam. Using the various placement options, you can try to hide it in a corner (nearst or aligned), at the rear or at random points. As OP has discovered, random is often not pleasing on a cylindrical print with no corners.
The best you can do is mitigate the effect. Calibrating your filament (diameter, extrusion multiplier and linear advance) is essential to minimize over-extrusion, which can lead to exaggerated z-seam bumps. That will reduce the seam as much as possible. Then you have to decide how to try to hide them. On cylindrical surfaces, you often want to align them to ease post-processing with sanding and filling.
RE: Bubbles (Hickup) in cylindrical Prints
On cylindrical surfaces, you often want to align them to ease post-processing with sanding and filling.
On my mechanical parts that need to be smooth around their entire circumference, I take the opposite approach. I intentionally make PrusaSlicer produce random seam positions so they are not aligned. Rather than a prominent defect at at one angle, I get little bumps scattered at different places. Spinning sanding off the little bumps gets down to a smooth, round surface pretty quickly. If I let print with an aligned seam, sanding that portion without creating a localized roundness defect is difficult for me. Now if the part only needs to look smooth, I would do it with an aligned seam, but my mechanical parts need to be actually round.
One example of 3D printed mechanical parts is my Vasa Ergometer pulley upgrade https://www.thingiverse.com/thing:3895168
Those need to be mechanically round when finished. So, I print those with random seam positions.
RE: Bubbles (Hickup) in cylindrical Prints
As @bobstro and @guy-k2 indicate the issue is due to the start-after-move (seam) action. You see a slight tapering-off at the blob that shows that during the move to start the next point a slight ooze occurs and is deposited at that point then tails off as the extrusion progresses. Calibration of the filament helps as does decreasing pressure in the nozzle by increasing retraction but over-retraction at every move has its own issues. Depending on the accuracy needed you can also under-extrude to help and Prusa does this by default; if you check flow rate during a print run you will see it is set to 95%. Picking a uniform start point for each layer is the best option to aid clean-up as @guy-k2 suggests. Nozzle size and temperature will affect ooze too, as will filament type and I always do a print test for each new batch, colour type of filament; the test part has curves, walls and a hole to check dimensions and filament performance as shown. The size of the piece is 20 x 50 x 4mm with a 10mm dia hole and 2mm walls. Bending and twisting this part also tests for layer adhesion too.
