Bondtech gears eccentric?
I have installed the MK3S/MMU2S upgrade and I find that it looks as if the bondtech gears are somehow eccentric? That is, as the extruder turns, the door moves in and out by a fraction of a millimeter, repeating every time the extruder motor makes a full turn. This happens both with and without filament in the gears. I have brushed both the filament-gripping teeth and the teeth that connect the two gears with a brass wire brush. I suppose it could be something wrong with the extruder stepper, but it seems to run smoothly. I have both bearings in the idler and I have rechecked the set screw and seating of the bondtech gear on the extruder motor shaft. What is going on?
Print quality with single filaments is rather uneven and stringy but mostly works. The multimaterial is completely unreliable but I suspect other causes for that, though if the IR sensor is being erratically triggered that can't help the situation.
RE: Bondtech gears eccentric?
look to see if the grub screw in the bondtech gears is seated . if it is above the the body of the gear it can hit the idler gear and move the door. easy test is move the extruder motor with no filament - the door should not move
RE: Bondtech gears eccentric?
Here is a video of a loading sequence that shows the door moving before the filament is loaded:
RE: Bondtech gears eccentric?
that is exactly what a extruder with the bondtech grub screw not fully seated will look like
RE: Bondtech gears eccentric?
Hmm. The set screw does look like it protrudes slightly from the Bondtech, but it is tightened down and centered (as far as I can tell, wiggled it while tightening) on the flat side of the extruder motor shaft. Surely this set screw can't be longer than the others? I slid the extruder gear back and forth and don't see any sign of obstructions. I guess I have to disassemble the whole extruder to get at it?
RE: Bondtech gears eccentric?
you should be able to command the E motor from the control panel and watch the door, when the door moves out ( or the flag moves in) you can open the door to see if the grub screw is in a location that would hit the idler
RE: Bondtech gears eccentric?
The set screw must be centered on the shaft flat. If it isn't it will protrude. You might be surprised how many people just put the gear on and tighten, paying no attention to the flat. So it is a common mistake and nothing to be ashamed of.
I fully loosen the set screw so the gear is free to spin on the shaft. Position the flat so it is facing me, then align the set screw best I can by eye, then slowly tighten the screw while wiggling it side to side making sure the flat on the screw fully contacts the flat on the shaft. Once I get the screw "set" on the shaft, I do the final torque.
ps: and there is always the chance the gear isn't machined correctly and is eccentric. But it's unlikely.
While in there, check that the axle for the idler screw is midway in the two ears. The shaft is too short and if not pushed in will fall off one of the ears, causing all sorts of extrusion problems.
RE: Bondtech gears eccentric?
I fully loosen the set screw so the gear is free to spin on the shaft. Position the flat so it is facing me, then align the set screw best I can by eye, then slowly tighten the screw while wiggling it side to side making sure the flat on the screw fully contacts the flat on the shaft. Once I get the screw "set" on the shaft, I do the final torque.
Yes, this is how I tighten down the set screw. I've also loosened it and re-tightened several times now, with no visible change. The set screw still protrudes, even when all the way tightened on the flat. I'm not sure what's up.
I've spun the idler and don't see any eccentricity, or any sign of the axle being out of place. Likewise the gear on the extruder motor doesn't show signs of being off-axis when I peer in through the removed door. But the motion is fairly subtle, so I might not see it? For now I'm going to put up with it and chase other problems; I'll take a closer look when I have to take the extruder apart to swap in the MMU2 heatbreak.
RE: Bondtech gears eccentric?
check the length of the grub screw, it should be 2mm long if it's longer, you have the wrong screw.
the thermistor in the heatblock is retained with a longer grub screw, maybe they somehow got mixed up, if you built the kit, there should be a spare, in the spares bag!,
regards 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
RE: Bondtech gears eccentric?
What Joan said!
And post a photo of the offending Bondtech gear positioned to see the set screw, and a shot of the idler gear in the door. Could be something none of us are thinking about.