Stephan,
from my own measurements of several local mounts, correspondence with people o/s, plus comments from yahoo group.
The mounts with +/- 20 arc sec errors are faulty. The problem with them is in faulty machining of the worm.
The worm is machined and then the end journals that fit into the ball bearings are ground. The problem is that some mounts have the journal on the end that the spur gear fits ground off center. You can fairly accurately predict the periodic error of an individual mount by measuring with a dial guage and v blocks the wobble in the worm. The good ones have about 1/2 a thou or less of wobble which seems to fairly reliably predict a total pe of around 10-15 arc secs. Those that have a total of 40 arc secs will have a wobble of about 2.5-3 thou. The problem with the larger wobbles are that the speed of the pe becomes horrendous. My "dud" mount moves 20 arc secs in 30 seconds on 2 places in the worm cycle - autoguiding simply cannot keep up with this. The actual worm thread is very well machined, but has some mild surface roughness.
cheers
Gary
Quote:
Originally Posted by Stephan
Gary,
Where did you get this number from? The only internet-published PE-recordings I found showed PE's of around +/- 20 arc Secs.
Stephan
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