Quote:
Originally Posted by gregbradley
I read in the Bisque PMX manual that mostly errors in the worm (20 microns) cause the PE. 20 microns is a pretty small size. I assume that figure is larger for less well machined worms.
Greg.
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Greg, the accuracy of the machining process will be neither here or there these days as the vast majority of worms and worm wheels would be cut on CNC machines with better than 0.01 mm accuracy as it would be the only way to meet mass production quota's. The real difference is made in what takes place after the machining process to clean up the worms and this is usually in the form of lapping with various grades of diamond grits to remove the lumps. It is very time consuming hence the extra cost. Brendan Mitchell spent quite a bit of time lapping his worm gear mesh on a simple EQ6 and gets fantastic PE figures but he has also set the gear mesh clearances' very well to. Another factor is the size and number of teeth on the worm wheel itself, basically bigger is better as small errors will be less pronounce and mount builders such as SB and AP always use large wheels on the RA for that reason. It is best to view the machining process as a raw stage before final finishing. Mass produced mounts such as those made by celestron, meade, skywatcher etc do not have the same attention to lapping as something like a PME/PMX or AP mount but they don't need to as the profit margin is not there. Other things such as worm block design and run out in the worm itself will also come into play but these will affect backlash more then anything else.
Andrew, why not give it a shot on a cheap mount and see what happens. My EM200 has the encoders on the end of the worm so you might be on to something.
Mark