Motor cog turning itself lose

Hey,

I recently switched to a geared extruder and everything works fine except that the cog thats on the motor shaft is coming lose all the time.
I have one similar to this

and modified the the bore to a D shape and reinforced the head to be able to screw it tighter and not break the plastic, but it came lose again. Anything im not seeing here?

Edited 4 time(s). Last edit at 11/27/2014 10:21AM by sungod3k.

Is the screw backing out or the plastic deforming?

If the screw's backing out, can you fit a nyloc nut in the nut trap? Either that, or a drop of super glue on the screw should stop it backing out.

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Both, I feel if I screw it any tighter it will start breaking the plastic.

But a locknut makes sense. Im gonna try that.

Edited 1 time(s). Last edit at 11/27/2014 06:27PM by sungod3k.

I use a similar gear on my Wades extruder. On mine there is a slot to take a square nut and then a grub screw screws into that. I also filed a flat on the motor shaft.