[doug_parkes]

I once owned a G8 and a G11 Losmandy mount. After a while, both mounts exhibited the same fault—lost motion on both shafts. If the worm/worm-wheel engagement is correct and you still have some lost motion then your mount probably has this fault too.

I had lots of backlash problems which turned out to be caused by the set screws that hold the end-cap of both the RA & Dec axis onto the shaft, progressively coming loose.

To check if you have this fault, tighten the clutch knobs and hold the OTA and attempt to rock it back and forth in RA & Dec travel. If you discover any excess movement then the set-screw retaining the end-cap onto the particular (RA or Dec) shaft is loose. My C11 had more than 1° of movement. (One year, at the SPSP, I did a little survey and found four other Losmandy mounts with the same fault).

I fixed the problem by machining a V-shaped groove into the shaft (it is normally a flat ground onto the shaft but the tip of the set-screw 'rocks' on the flat) and replacing the original set-screw with two shorter ones. By tightening down the first and then tightening down the second onto the first (providing a lock-nut effect) the lost motion disappeared since the end caps were again firmly locked to the shafts. I used Lock-Tite to assist in locking the set-screws. The main thing is to be aware that the set-screws can loosen and check them frequently.

The Losmandy mount performs very well and provided they are well maintained, they will give very good service.