Does anyone know of a source for undersized needle bearings to fix a
weakness in my Losmandy G11 mount? Specifically, 1.247" ID / 1.500 nominal
OD. For the benefit of those who may encounter the same problem, I have
described it below:
With a nominal vertical load, the RA and/or DEC shafts on my G11 mount tend
to 'hang' about .002"-.003" below the axis centerline when the clutches are
relaxed. When the clutches are tighten, the shaft end plate initially
'locks' to the nylon clutch surface slightly below center. When the axis is
rotated far enough that the weight overcomes the grip of the nylon surface,
the axis 'shifts' into a 'more' aligned position. This is normal behavior on
four different mounts that I have examined. Besides introducing tracking
errors, this misalignment distorts the worm/wheel spacing by a small amount,
and causes the backlash to vary as the axis is rotated through 360 degrees.
Changing the load on the mount, or loosening and retightening the clutches
can completely upset prior backlash adjustments. If you are not adjusting
your worm/wheel spacing for absolute minimum backlash, you may never
encounter this aspect of the problem.
The needle bearings on both the RA and DEC are set back about 2" from the
'business end' on each axis. As an experiment, I pressed an additional
1.250" ID needle bearing into the opening so that the shaft was supported
nearly to the end of the opening. Additionally, the shafts I have seen
measured 1.2470" dia instead of an optimal 1.250". I wrapped some .0015"
stainless steel shim stock around the undersized shafts as a temporary fix
to remove the bearing slop.
Well, it was like night and day. That simple change eliminated the
'shifting' on each axis, improved tracking and GOTO pointing accuracy
dramatically, there was no more slop in either axis, and best of all, the
backlash can be adjusted to virtually zero through a full 360 degrees of
rotation.
Anyone else have a similar experience?
Neal
