Small blobs on underside of prints
Hello everyone! I started encountering a new issue with my MK3.9 where small blobs/bumps appear on the underside of my prints. It does not seem to happen on the topside, and this happens across multiple filaments so I'm a bit stumped what the cause could be. Does anyone have any ideas?
Slice your model in the usual way then save your project as a .3mf file
Files > Save Project as
Zip the .3mf and post it here. It will contain both your part and your settings for us to diagnose.
RE: Small blobs on underside of prints
Thank you! Here is the project from PrusaSlicer 2.8.0 zipped up.
RE: Small blobs on underside of prints
I'm confused by the photo. Looks like a top down view. If it's the view from the bottom, I assume you were using supports, so are these pock marks from the supports?
Formerly known on this forum as @fuchsr -- until all hell broke loose with the forum software...
RE: Small blobs on underside of prints
Apologies for the confusion. Yes, I did use supports but I did not saved the sliced model as a project before I closed PrusaSlicer. Supports were used only between the legs and the small overhang on the hat, but you can see the bumps/blobs are present in numerous other areas.
I have another example of a different model which showed similar behavior and no supports were used. Again, I don't have the original sliced file saved as a project but I ran it through again and saved it. The model is here: https://www.printables.com/model/950460-kobo-stylus-2metapen-m2-protective-enclosure
I sanded off the bumps, but you can clearly see areas where they were present and in this case it was only present in layers close to the "DIABLO" logo, further up the tube they are absent.
As posted your figurine not prepared for printing - slice your model as if you were about to print it then save your project as a .3mf file - that way your settings are included.
Your tube would be improved if the text was chamfered, as it is there are unsupported overhangs causing at least some of your problem.
Cheerio,
RE: Small blobs on underside of prints
I prepared another similar model to the figurine, sliced, saved the project as a .3mf and then printed it. The same artifacts can easily be seen. Mini Stay Puft annoyed.3mf stay-puft-2
RE: Small blobs on underside of prints
Would there be any specific settings which may contribute to this issue that I can look over? I'm fairly certain I'm using the default profiles for my printer. Or alternatively, could there be something physical on the printer itself that I could investigate? I tried a cold pull recently and not certain it had any effect.
It's a new behavior and makes things difficult as the prints require post-processing now to remove these, and I cannot find many examples (if any) of this particular type of artifact being mentioned.
Appreciate any help in getting to the bottom of this.
Thank you. There is nothing obvious in your settings and in the new images you provided the same bumps appear on your supports - this suggests that in this case the issue may be with the filament.
Try a different, freshly dried, filament - no need to complete the print; to reduce waste you can stop it if/as soon as, the the problems reappear.
Cheerio,
RE: Small blobs on underside of prints
I opened a fresh roll of Prusament PLA, tossed in the dryer for good measure and unfortunately the artifacts still appear.
I don't undertand why they only show up in certain areas on the print. It suggests to me something to do with the hotend or it's movement. Do you have any further ideas for troubleshooting?
RE: Small blobs on underside of prints
Well, I have another update and believe I figured out the issue. Short answer: it's related to the overhangs, specifically enabling dynamic overhang speeds.
Longer answer: I watched the printer carefully while doing another test print and noticed something I recalled seeing recently - the printer motion is somewhat "jerky" when printing overhangs. This is different from acceleration jerk, this is a non-smooth motion while laying down a curved trace.
I also tried a different printing profile, and noticed the results were significantly better with a SPEED profile, but they still existed. Comparing the profiles, I saw there was differences in the dynamic overhang speeds and looked into the setting. It perfectly describes what I was seeing - the printer was slowing down rapidly at times when printing overhangs, which explains the jerky motion I saw. I'm guessing it's a bit of overextrusion which happens when the print head slows down so quickly.
I tried disabling these completely, and the issue went away. I do see the value in having that setting though, but not at the cost of artifacts. Has anyone encountered this before?
I captured a few videos showing the jerky hotend movement and can upload if there is any interest.