I've decided to drop the Arduino method and just use gcode to change the tools. Much simpler wiring and seems quite straightforward.

However, this lead onto some problems with the turret. Sometimes it would turn and others it wouldn't, either backwards or forwards.

I've stripped it down tonight and found a number of things.

First is that you have to remove the X axis stepper to gain access to the hole through which you release the shaft of the turret stepper.

Having removed the turret and gained access to the cam and pawl, the seemed to be an excessive amount of force required for the cam to push back the pawl.

The pawl tension is adjusted by the screw which passes through a stack of disc springs. Backing that off just a little eased the pressure to the point where the turret rotated freely.

With it all apart, I've taken the opportunity to lubricate all the sliding surfaces.

Whilst putting it all back together again, I found that there should be two alignment dowels between the turret itself and the shaft which powers it. These are missing, so the only thing holding it in place are the four fixing screws. As there is some clearance in their holes, the slop I could feel when manually handling the turret were caused by it slipping on the shaft. Two 5x15 dowels are required to keep the turret true.

Adrian.