I have finally managed to get around to printing the replacement cog:

Gear of misfortune

using nylon, but I’ve discovered an issue with the 3D model I’m using.

If you look closely at the original cog you see that teeth rise from left to right.

but the model I was given (above) has the teeth falling from left to rise. That is, in the opposite direction to the original. This would explain the friction I’m getting when I insert this new wheel.

I got this model from the people I sent it originally to, who failed to produce a suitable result. It now looks like I’ll need to model the whole thing myself from scratch. Painful.

The cog I have printed using the model with the wrong teeth does work but it is a tight and doesn’t move as freely as cog with the correct teeth.

Back to the drawing board.