Kinda like optical surface accuracy, I wish the manufacturers would state that the periodic errors are typically specified as +/- xx arcseconds (so the total p-v error is twice the value specified). Come to think of it, I wish manufacturers would just specify and guarantee some value!
I had an old Byers mount that exhibited +/- 7 arcseconds (used a sector of an ~12inch dia gear). My current Losmandy GM200 uses a 9inch Byers gear (and a Losmandy worm) - with some tweaking I now get +/- 3.5 arcseconds. My first go at this mount was +/- 8 arcseconds. I ended up replacing the worm and got it down to the 3.5 range. Anything under +/- 5 arcseconds is quite good, indeed and I think that the 30 arcsecond figure for the Super Polaris is not all that bad considering the size of the gear and its cost.
> I also think this post is fair game if the owner of a commercial scope wants
> advice to modify it. If we turn these people off the ATM list will die.
> There is a lot more to telescope making then grooving pitch <G>
> Telescope making consists of optics, mechanics, electronics,and structures.
> Thats way I love this hobby. Now I will get off my soap box.
> PS I forgot computers and software.
> Bob Pfaff
>
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I have heard of some improvements made in worm/gear set accuracies by lapping them (presumably removes some of the high spots on the worm/gear). I wouldn't expect this to substantially improve the main component of the periodic error (usually the eccentricity of the worm 'thread' in relation to its rotational axis). Still if a set exhibits some large erratic errors, lapping may help. This can be done by placing some fine grit (not sure of what grit size to use, probably 500 grit or finer) into the worm mesh and then spinning the worm using a hand drill (and also putting some load on the worm gear). I would lap both sides (reverse the drill periodically) and would be very careful not to get grit into any bearings...
Bob