How to deal with zits/blobs?
I'm trying to eliminate or reduce zits that appear on side walls. Generally I can scrape these off with a fingernail, but it's annoying enough I'd like to address it.
I believe the zits are deposited when a new line of filament starts. I first had the seam position set to "nearest" and all the zits started in about the same place vertically on a wall. I changed the seam to "random" and now the zits started, well, randomly over the wall. I am printing with PETG at 240C for the first layer, 230C after the first layer. I have two MK3S printers and one shows this issue much more than the other despite using the same filament and settings.
I have read several problem solving guides and they all talk primarily about retraction settings. However they don't really give any guidance on how to set retraction. I've tried anywhere from 0.2mm to 0.8mm retraction but nothing seems to change the result, however I don't know if that's too much or too little retraction.
Any advice on retraction settings or what other setting besides retraction might be helpful?
RE: How to deal with zits/blobs?
I went way down the rabbit hole of trying to improve print quality. Stringing was my primary concern, but "zits" were a pervasive problem as well. After much experimentation, I realized that calibration of the extrusion multiplier is key. If the filament diameter and extrusion multiplier are incorrect, your slicer is generating gcode using parameters that might not match your actual printer and filament characteristics. When this happens, you will get either slight over extrusion or under extrusion. A bit of over extrusion will tend to accumulate at the end of an extrusion. This can result in
- Stringing between vertical parts
- Zits and blobs on vertical printed surfaces
- Ugly z-seams created when the nozzle is moved to the next layer
- Irregular exterior walls when printing parts with multiple internal infill variations
- Uneven top surfaces
If you read up on "zits" or "stinging", you'll find a wealth of recommendations for work-arounds, including:
- retraction and de-retraction length
- retract/de-retract filament speeds
- wiping
- z-lift or z-hop
- coasting (Cura)
The lightbulb moment for me was when I realized these are workarounds for problems like over extrusion. Eliminate the over extrusions and the need for workarounds goes down. Mind you, you won't get perfection with a consumer-grade FFF printer, but you can certainly get closer.
After going through this process, I can get by with:
- 0.2-0.4mm retraction.
- 0.4mm z-lift
- No wiping
Overall print quality is improved, stringing is mostly gone, zits and z-seam quality are much improved (although the seam never goes away completely). I find that using Aligned or Nearest for the seam position gets rid of any remaining zits on walls from using Random positioning. They seam still shows on rounded surfaces since there's no corner to tuck it into, but I can hide it or post-process it much more easily if it's aligned.
I've got a bunch of notes on the process I used here if you're interested.
and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: How to deal with zits/blobs?
@bobstro
I get the feeling you've said this before (copy/paste) 😀
I tried messing around with the extrusion multiplier a few months back and it only seemed to make things worse (I didn't change anything drastically), but I understand the machine a bit better now so I'll try again when I get a break in the printing schedule.
For the time being I'll try raising the z-lift a little which is currently set at 0, and also try "aligned" for the seam position and see how it goes. The other retraction settings I got from your excellent notes.
RE: How to deal with zits/blobs?
I cut & paste the main bits to avoid missing anything important. Otherwise, it depends on the level of effort the poster has gone to. It's easy to forget important details, so I like to have notes with a good foundation ready to go.
In your case, definitely try moving the z-seam location around. If the zits are due to retractions, that should help quite a bit.
and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: How to deal with zits/blobs?
I had numerous issues with blobs/boogers in PETG. I solved them at first with dropping the extrusion multiplier, but when I got down to below .9 I felt something else had to be at play. I ended up buying the E3D PRO(the pro is important) for the extruders(I have two MK3Spluses).
Now I print with Generic PETG profile with zero boogers/blobs. I picked up a pack of 3 of these on amazon
https://www.amazon.com/gp/product/B07779TP4S/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1
RE: How to deal with zits/blobs?
I had numerous issues with blobs/boogers in PETG. I solved them at first with dropping the extrusion multiplier, but when I got down to below .9 I felt something else had to be at play. I ended up buying the E3D PRO(the pro is important) for the extruders(I have two MK3Spluses).
Now I print with Generic PETG profile with zero boogers/blobs. I picked up a pack of 3 of these on amazon
https://www.amazon.com/gp/product/B07779TP4S/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1
I already have those on my hot ends.
Changing the seam position to "aligned" definitely seemed to help, but I also some improvement switching nozzles from a standard brass nozzle to a Micro-Swiss plated nozzle. It's still not perfect but better.
RE: How to deal with zits/blobs?
@buckeyestargazer
interesting. Both my printers I bought assembled so I never had to really muck with belts, etc. I did recently upgrade one of them to an MMU2S, but that's a different story...
I fought with the blob/booger thing though. it was so frustrating. I had several cases where the blob dropped on the model and eventually triggered crash detection. The generic profile prints at 230/85 deg for the first layer and then 240/90 for subsequent layers. Now, honestly, I have several vendors' PETG and all of them print cleanly with the Generic PETG profile since adding the socks.
Do you live in a humid climate, could there be moisture in your filament? I live in Colorado and it's the opposite of humid. In fact it's TOO DRY most of the time. So dry that I have to keep a ground accessible to touch when transferring memory cards between pc and printers or going going the few steps to manipulate the printer in some way. It's really crazy. While I do keep all my filaments bagged with desiccant, I don't worry about having the filament out for 24+ hour prints.