prusa needs to fix the bondtech idler shaft
I've had my mk3 for well over a year and it has worked like a champ. Great prints. Well for the last three months I've had nothing but shit results on my mk3. I tried everything from drying filament, atomic pull to making sure everything was tight. It still printed like crap. Poor layer adhesion and under extrusion. I've been trolling thru the forums and youtube about the under extrusion and layer problems. I finally came across this video about the bond tech idler shaft being able to slide out of the plastic holder. Watch "Prusa MK3 — Working Solution for Clicking Extruder, Under Extrusion or Inconsistent Prince!" on YouTube
Guess what that's the exact problem i had. I reset the shaft and now it prints like a prusa should. But the real problem is either the idler shaft is 3mm to short or the printed part shaft holder is 3mm too long. If the shaft walks to one side, the shaft will be flush to the outside of one holder and not even in the other holder. So if you are looking at the idler you would never know what was wrong. Only if you push on the bondtech gear would you feel a slight flex and that is all it needs.
Here is how i tested to find that there was something wrong with extruder.
Have filament loaded in the printer.
Measured 100mm above top of extruder filament inlet.
Mark filament with a sharpie.
Reset printer by pushing x on from panel.
Heat hotend to proper filament temperature.
Go to movement, extruder, and turn dial slowly from 0 until it reads 100.
Watch the mark. The mark should be right at the extruder filament inlet. This means the extruder is feeding the filament correctly.
When I first did this test my results was the mark was 28mm from the extruder filament inlet.
The idler plastic holder probably needs to be modified so this problem can not happen or when it does it becomes obvious.
Re: prusa needs to fix the bondtech idler shaft
It appears to have been addressed in the Mk3S variant; there is less space between the ears on the door that hold the shaft.
Re: prusa needs to fix the bondtech idler shaft
Great my mk3s upgrade kit will be here an monday
Re: prusa needs to fix the bondtech idler shaft
I am pretty sure I spotted this when I did my build and ended up buying some longer pins and cutting them to length so they fitted properly... So I never thought about this again...
Re: prusa needs to fix the bondtech idler shaft
Thanks, my MK3 started to act up weirdly and watching the video I recognized the exact same problems.
I did the marker test and in fact the extrusion was way off (50 extruded instead of 100!)
Checked the bondtech gear on the extruder idler and it got twisted by the pressure on it, now luckily I've a 2nd working prusa and I'll reprint the idler but I think that Prusa should release an update for the MK3 idler without having to buy the MK3S upgrade since it's flawed (it's the second time that idler fails)
RE: prusa needs to fix the bondtech idler shaft
Thank you for your thought and YouTube video. I checked the idler and the shaft it was barely into one side. But there was no "wiggle" to the idler gear. I still centered the shaft hoping that a "wiggle" was there, just too small to see. Unfortunately, it had no effect at all. One would wonder why Prusa doesn't supply a shaft that is 3 or 4 mm longer so it fits more evenly in the printed part. My hot end parts arrive tomorrow, so I will totally disassemble and reassemble the hot end and hope that resolves the issue. My printer has worked perfectly for years until this.
RE: prusa needs to fix the bondtech idler shaft
I have the MK3S with the + upgrade, and in my case the pin routinely falls out of its hole and the idler cocks out of alignment. Usually this causes a clicking sound that is slightly different than you get with a jam, but it happens so frequently that it's the first thing I check when I get under extrusion. The pin itself seems too short and the hole just slightly oversized. I've been meaning to modify my installation, but been pretty busy.
Now that it seems others have this problem, it seems apparent that this issue was not fixed with the MK3S.