Jack
Had a play with my setup last night and found that there was a slight play between the collimator body and its supporting frame so have now replaced the screw (was the one on the motor side) but have it screwed in just touching the collimator body to prevent unwanted tilt but at the same time not adding any force to tighten the turning of the body. All adjustment for tension on the collimator body is carried out by the screw on the opposite side.
I motorized the micrometer shaft so that I didn’t have to touch any of the kit during a session and I also run remotely so comes in handy. But the downside is the speed of the focus motor makes moving the grating from the Hb region to the Ha region painstakingly slow 🙁
Regards
Alun