Bondtech Extruder for Prusa MINI
Looking to get the right settings, using Prusament PETG and it strings like hell. I've set retraction to 2mm @ 50mm/s. Print temp bumped down from 250 to 240. 150mm for travel. 40mm for perimeters. Ill have to tinker with this all again soon though, replacing hotend with a Mosquito.
As a general principle, I would always try the stock hardware first before making "improvements". Remember that forums like this have a natural selection profile for folks with problems. I suspect (with zero data) that the majority of Mini owners has no issues. You can always replace parts later in case you run into issues.
Fuchsr is wise! Don't do anything until you have consistent problems you can reproduce, otherwise you won't know if you are really fixing them, or making more problems.
One thing I've just done which has helped a bit, I swapped back to a brass nozzle from a stainless steel one. I think this is helping with heat transfer to the filament and reducing clogging a little.
Indeed, the gif works. Thank you for the heads up!
I think you are on to the issue: I have printed some of the provided parts just fine and printed some of my own ok. When I started printing a part that had a short distance with a lot of retractions the problems started. No filament being extruded after about 30 minutes; extruder gear spi9nning but filament not moving.
I agree the filament has been worn down from the constant motion back and forth. Not sure a Bondtech extruder would fix this or do I just stay away from parts that look like they will cause this issue.
One of the advantages of the Bondtech extruder is that the pressure on the filament is adjusted with a fine pitch bolt giving you more control than with the stock extruder. Their recommendation in the instructions worked well for me.
Also replacing the stock feed tube with the higher quality Capricorn blue tubing which has tighter tolerance on the ID seems to have less friction which helps with consistent retraction.
You can tune the retraction using the information on Teaching Tech printer calibration website.
I changed the original extruder to a Bondtech, and an Olsson Ruby nozzle at the same time. Now my prints are fantastic and sometimes my mini lays a print that is so smooth and shiny like a glass surface. No need for ironing.
Else - I have no grinding and clicking as from the old extruder.
I have purchased the Bondtech heat break kit, but I have had no reason to install it yet.
Changing my Mini to a BondTech extruder
Why? The printer works ok with PETG but most prints with PLA end up with a grinding, non-functioning extruder. Some of the Prusa demo parts print ok but I suspect they were selected for good printing characteristics. I have not had success with any downloaded STL files printing in PLA. It seems that too many retractions grind a groove in the PLA, clog the drive gear, and result in no filament being extruded.
I checked the nozzle (not clogged), did cold pulls (no improvement), and adjusted the tension screw but it just seems that the extruder does not work with some files and PLA. The number of similar reports appears to back this up. I have none of these problems with PETG so I expect there are no problems with the printer, just the extruder and retractions.
Playing with the extruder and some pieces of filament show distinct differences when holding the filament and turning the gear: PLA quickly wears a groove and clogs the teeth; PETG does very little of this. It is interesting that PLA is specified as harder than PETG but that must not be the whole story. PETG grips with more force than PLA even though it does not wear as quickly.
I have had enough of disassembling and cleaning the extruder, I ordered a BondTech and expect that two drive gears will correct the problems.
*Update - the Bondtech extruder had some manufacturing/assembly issues that kept the serrated grooves from being in line with the filament path. IOW it did not work well and made some unpleasant noises. I adjusted one issue and used a diamond file to remove some flashing to correct the other issue, much better now. I should not have had to do this and I reported it to BondTech.
Still having problems with PLA so I checked the infamous hot end PTFE tube, it must have shrunk since I got the printer (3 months). I guess PETG is less susceptible to PTFE tube gap issues since there was not much of a gap. Anyway, I loosened the three grub screws, did the procedure, and now it prints ok with PLA (at least one part). Of course I had to rerun the first layer calibration and now it is near the limit so I have to adjust the Super Duper Pinda Minda and start over.
The length specification for the PTFE tube makes little sense, no one is likely to hold a tolerance of 0.1 mm on a piece of PTFE that has a slight curve to it anyway. And then the tube is compressed by about 0.25 mm (1/4 + turn on the fitting), making the 0.1 measurement kind of silly. Then there is the "precise" measurement of a credit card thickness...
Would the Prusa extruder have done as well as the BondTech after PTFE tube adjustment? Plenty of Minis are working ok with it and it worked ok when new so it must be a good design but the Bondtech has twice the number of drive gears and a better tensioner so if anything gets sticky it has a much better chance of not grinding the filament and continuing to work. Overall the printer requires much more maintenance and fiddling than I expected. Some of the reviews claimed it is plug and play but it seems they exaggerated and glossed over some issues. To me, 3D printers are still not ready for the casual user.
To me, 3D printers are still not ready for the casual user.
I would completely agree with you here!
Going back to my experiences with stock vs Bondtech extruder. The Bondtech is much grippier, with some types of filaments (glow in the dark, ivory) I found the stock extruder could slip and I would have under extrusion, and if I tightened the idler to fix that it would grind the filament. The Bondtech is so strong if I have a head clog it will break the olives on the PTFE tube that runs to the hot end. So it's definitely a lot better!
I upgraded the heatbreak to the Bondtech first, and that actually worked really well for me (apart from some filaments that I mentioned) most of the time. But the moment I added the new extruder I struggled with Prusament until I spent a lot of Benchys tuning things. I think this is because the Bondtech heatbreak cures the heat creep, and that the old extruder would slip a little so retracting was okay, but the new one doesn't slip at all and that seems to cause problems in the hot area.
My current theory, that invalidating my warranty and installing custom firmware is the only way I can verify, is that the fix for this problem might be just to lower the hot end fan (not the cooling fan) speed because it might be cooling too much of the Bondtech heatbreak.