can't fix PLA stringing
I'm trying to use PLA from Vertex/Conrad. I've done a lot of printing with their ABS, it's quite nice once you set +- 4mm of retraction length.
I've now got 2 reels of their PLA, silver and black, and they're very stringy. Plenty of prints fail because the first layers deposit very thick strings, the printer catches on to them and the print fails.
Raising the retraction to 2mm doesn't help, when raised to 4mm I get big holes in my print. I've tried increasing retraction speed from 30m/s to 100 and 120m/s, lowering temperatures to 190C and adding 25% or 50% of retract before wipe. Nothing helps and I'm looking for help. Here's a photo: bottom right for first print, top right for 4mm retract, left ones with various tweaks.
RE: can't fix PLA stringing
Ask the PLA manufacturer for suggestions. It's their plastic and they should know how best to print with it.
RE: can't fix PLA stringing
It can't hurt to dry the filament. Those retraction speeds seem pretty high. Typically 30-50 should be more than sufficient.
RE: can't fix PLA stringing
[...] Raising the retraction to 2mm doesn't help, when raised to 4mm I get big holes in my print.
A lot of the general advice you'll find on the Internet is meant for Bowden-style setups. The Mk3 has a direct-drive E3D V6 hotend. You should not use retraction lengths of more than 2mm or you will be pulling molten filament up from the hotend into the cold part of the assembly which is generally asking for trouble and jams.
As a quick test, disable z-hop (Printer Settings->Extruder 1->Retraction->Lift Z). This may reduce fine stringing but be aware that if you haven't done a good filament calibration, turning off z-hop may lead to scarring of top surfaces.
Be aware that many poor souls have been sucked into the rabbit hole of trying to eliminate stringing:
This was a test using PETG. The main finding is that results on tiny little diagnostic prints have little bearing on what you'll see in full-size prints. That spiky print you're using is intended to be a worst-case. If you're not seeing much of that same fine stringing in actual prints, I wouldn't worry about it.
For what it's worth, here's what I start with for retraction settings:
This gives me good results on the silly little diagnostic prints, and generally good results in production. I mostly use PLA & PETG though, so give it a try with ABS. Note the reduced de-retract speed. I've had good luck setting this per Michael Hackney's recommendations based on the non-Newtonian fluid behavior of molten filament
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: can't fix PLA stringing
[...] Raising the retraction to 2mm doesn't help, when raised to 4mm I get big holes in my print.
A lot of the general advice you'll find on the Internet is meant for Bowden-style setups. The Mk3 has a direct-drive E3D V6 hotend. You should not use retraction lengths of more than 2mm or you will be pulling molten filament up from the hotend into the cold part of the assembly which is generally asking for trouble and jams.
As a quick test, disable z-hop (Printer Settings->Extruder 1->Retraction->Lift Z). This may reduce fine stringing but be aware that if you haven't done a good filament calibration, turning off z-hop may lead to scarring of top surfaces.
oh, OK, I didn't know that bit about direct drive vs Bowden extruders. I'll try more with the "retract before wipe". I'll test your suggestions.
Prusament PLA extrudes just fine, and I've printed a lot of ABS/ASA without any stringing issues. I've already had 2 jams, where the filament broke off in the hotend, and I had to disassemble the hotend and replace the PTFE tube. This could be related.
RE: can't fix PLA stringing
Do you mean the filament snapped below the Bondtech gear but above the hotend? If so, next time this happens, try this:
- Raise Z to max.
- Open the extruder housing door.
- Inspect the top of the white PTFE tube below the gear. If you can see the top of the snapped filament, use tweezers to pull it out.
- Set nozzle temp to 285C.
- Use a 6in/15cm 1.5mm rod (e.g. brass available from hobby stores) or your hex wrench to poke down from the top, past the open Bondtech gear and into the PTFE tube. With any luck, you'll be able to push the stuck bit down into the hotend where it'll melt and be extracted, or at least far enough you can feed filament down after it.
- You can also try removing the nozzle and poking from below.
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: can't fix PLA stringing
Do you mean the filament snapped below the Bondtech gear but above the hotend? If so, next time this happens, try this:
- Raise Z to max.
- Open the extruder housing door.
- Inspect the top of the white PTFE tube below the gear. If you can see the top of the snapped filament, use tweezers to pull it out.
- Set nozzle temp to 285C.
- Use a 6in/15cm 1.5mm rod (e.g. brass available from hobby stores) or your hex wrench to poke down from the top, past the open Bondtech gear and into the PTFE tube. With any luck, you'll be able to push the stuck bit down into the hotend where it'll melt and be extracted, or at least far enough you can feed filament down after it.
- You can also try removing the nozzle and poking from below.
Indeed, it broke off like that. I tried heating and poking it, doesn't work. In the end I have to disassemble, heat up the extruder well, and then I can remove the PTFE sheath with strong pulling.
RE: can't fix PLA stringing
the PTFE tube is retained by a black ring, this ring grips the tube when pulled, but if you press the ring towards the heatsink, the ptfe should come out, easily!
Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK