On 3/31/2021 2:10 AM, John Kmetz wrote:
Reading through the white paper the following can be summarized:
1) A 76 second error is due to the bearings hanging up momentarily
2) A 76 seconds error can't be removed with a PEC curve since it won't overlap with the worm period
3) Some bearings have slightly defective balls or races
4) Some Losmandy worm blocks have a bearing seat which is minutely elliptical to the point where it will deform the bearing causing the balls to hang up
I believe another more likely explanation is that the balls are intentionally slightly undersized for the races to prevent binding. Under this condition, unless the bearing has some preload AND the load is exactly perpendicular to the bearing face, the radial load (ie., worm penetration) will be transferred from one ball to the next as the bearing rotates. This transfer causes a slight radial perturbation in the shaft that translates into unwanted periodic error.
A bearing producing a 76 second signal is quite likely not "defective". It is merely operating as designed.... just not optimally installed. If sufficient axial preload is applied to the bearing(s), all balls will be in contact with the races at all times and there will be no ball to ball transfer of load. Unfortunately, there is no preload adjustment in the Losmandy worm block design like there is in my venerable LX200 so the only way to preload the bearings is to squeeze the bearing blocks together while tightening the cover screws.... and hope that in the process you end up with the bearing blocks exactly perpendicular to the shaft.
Paul G.
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Paul Goelz
Rochester Hills, MI USA
pgoelz@...
www.pgoelz.com
