Thanks for the added information Steve.
"One unexpected design shortcoming is that the locking knob that is tightened against the balance shaft to secure the dovetail clamp has a quite sharp point on it. So it has a very small bearing point on the shaft and has to be done up very tight to stop the whole cradle rotating on the shaft. At some stage I'll fashion a tool to hold the knob in the lathe and flatten the end to give a much greater bearing surface. Another solution would be a nylon tipped locking knob."
Would filing/grinding a small flat on the shaft be an option? After all it's your shaft not mine.
Maybe fit ball races in each side of the saddle so the battery holder remains Horizontal regardless of the OTA position?
Rgds
Michael