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selmo

Grubby Grubs

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So I've had my UM2 for a week now, and the stupid grub screw on the extruder feeder shaft sleeve keeps unscrewing itself. First time happened on my third small print, and it's happened twice more since. Sheesh. It doesn't appear to be stripped... yet...it's actually working its way out. I'm sure if I have to keep tightening it, it'll be stripped soon. Has anyone needed / used loctite or similar threadlocker on it?

Is there any way to tighten the grub screw without dismantling the whole extruder feed mechanism? It's a heck of a lot of hassle -- having the spring shoot out, the extr motor plop out the backside (and you can't support it from behind), etc. That extruder feeder strikes me as really not well thought out, in several ways.

Has anyone had any luck replacing the sleeve with something like a MK8 extruder drive gear? I've got a couple and am curious if they're any better....I assume that would require adjusting the steps per mm for the extruder in the firmware.

I've printed Robert's alternate feeder mechanism, which looks like a smarter design. Much more open and accessible, if nothing else. If that stupid grub unscrews again, which I'm sure it will, I'll probably swap in that feeder mechanism.

 

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You can set steps/mm using gcodes and save it permanently also. Post again if you ever need to but the quick answer is to install repetier host, command say 100mm of travel and see what actual distance is (with filament only half way down the tube or command it to unextrude. Then find the ratio of error and correct steps/mm by that amount. RH will tell you the current steps/mm when it connects to the printer through usb and you can adjust this and save it (I think M500 might be the save command).

As far as loctite - I hope someone else answers. I know there are several types (colors) - some are meant for permanent and some will be "breakable".

 

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The grub screw should make contact with the flat part of the motor axle. Can you disassemble and see if this is the case? We've seen machine that seems to have been assembled the wrong way and thus the grub screw would need to be loosened again and again...proper solution would be to mount it towrds the flattened part.

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Yes, it screws into / against the flat side of the shaft.

I may try replacing it with another grub screw -- maybe there's something wrong with that particular screw? I don't recall if it's a conical / pointed tip screw -- a cup or flat tip would be less likely to unscrew under load here.

That and some (blue) Loctite.

And a new feeder.

 

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I replaced the grub screw with a new one, and it's still working it's way loose, but it's holding longer than the original one -- it should last me until parts arrive for my next step(s).

 

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