[Shiraz (Ray)]

Hi Lee. I take it that you are adjusting the gear mesh as tight as possible without binding and are finding that you get different mesh backlash at different DEC angles? I think that all mounts have this issue to a greater or lesser extent - unless the gears are spring loaded or unless you happen to have fluked a combination of bearings, shafts and gears where the various unavoidable run-outs cancel out.

Fix it by slightly un-balancing the DEC axis so that there is always some load to keep the gear faces in contact on only one side when in mesh (I use a small lead weight that I clip onto an appropriate position on the OTA). Probably also a good idea to make sure that the bearings are turning freely at all DEC angles as well - stiction can reduce the effectiveness of this method. You would probably have to unbalance any mount without spring loaded worms, so it doesn't really make any difference to the outcome if the backlash varies a little or a lot in your particular mount. There is no real point in trying to fix it unless you are concerned that your mount must be perfect, even if it won't make any difference to your imaging - then you could try some high ABEC main bearings as a first step.