Filament drive set-screw backing out

Kossel Mini, Airtripper's with mk8 drive gear, 1.75mm PLA, E3D v6 @ 205C.

I use a lot of retract, because of my Bowden tube, and my drive gear set screw keeps backing out. I filed a flat on the stepper shaft, added blue Loctite, and used a brand-new grub screw. I tightened the screw until it almost stripped. It still backed out after just a few prints.

Any ideas? I could use red Loctite or just epoxy the drive gear on, but I'd like it to be removable. There's not enough space to use a non-grub m3. What else would you suggest?

For applications that reverse you often see two set screws stacked into the same hole. The second set screw is tightened onto the first to prevent it from backing out. It sounds kind of wonky but works very well. It is also incredibly frustrating if you are trying to disassemble it and don't realize that there are two set screws.

All mine nip up nicely and dont move.
The internal thread on the drive gear must be a very loose fit for it to be that bad.
It could have been cut badly in manufacture.
Does it feel sloppy before it locks if you wind a longer screw into the thread?
And obviuosly too small to tap out to the next size up. Or re thread to the same size with a helicoil or thread sert.

You may have to try a new one.
As you know youl need to remove it as soon as you glue it in place.

Gordon

Edited 1 time(s). Last edit at 04/17/2015 02:40PM by gordonendersby.