Polishing worm and wheel for better PE?

[2stroke (Jay)]

Has anyone got a good guide or hand on personally experience polishing their worm and wheel to improve PE. I came across this http://helixgate.net/Odd_Ends/raworm.html and are thinking of trying it out first on a eq5 as a testing ground before moving onto the next victim. The results look great and would like to hear from someone who has done this to cheap mounts with brass worms, don't wanna screw one up if i don't have to lol.

[Tandum (Robin)]

I'd like to know why PE is so important if your guiding.
I measured my PE while guiding and it was decimals of an arc/sec.

[2stroke (Jay)]

When bumping up to high f ratio's everything helps Planing on making a portable wind shield when i get the chance. Also it will let you use less aggressive settings in phd ect so you can bump up the f ratio and have no eggs. But i guess your right for the common person just using something like an ed80 or f4/5 newt ect at prime focus with no barlow in the mix.

[asimov (John)]

Yes, I did this to my EQ6 almost a year ago. Take note that I'm still high FL imaging with it..

I'd say it took 75% of the PE out of the mount.

[naskies (Dave)]

Originally Posted by Tandum

I'd like to know why PE is so important if your guiding.
I measured my PE while guiding and it was decimals of an arc/sec.

Overall peak-to-peak PE doesn't matter so much with guiding, especially at short focal lengths, but the smoothness (or jaggedness) of the PE curve does matter.

If your PE makes a sudden jump - like 3 arc secs in one second - then if you are guiding with 1 to 3 second exposures with an image scale of say 1 arc sec per pixel you'll get some very eggy stars.

[marki]

Better off lapping the worm and wheel together with a fine grit paste, that way you get both and better match one to the other. Wont help a bit if the worm and wheel are below par though as this cannot be fixed. It works best on accurately cut worms.

Mark

[2stroke (Jay)]

Originally Posted by marki

Better off lapping the worm and wheel together with a fine grit paste, that way you get both and better match one to the other. Wont help a bit if the worm and wheel are below par though as this cannot be fixed. It works best on accurately cut worms.

Mark

Was thinking of that but the worm is brass and the wheel some kinda of alloy mix. If i did the brass worm would be chewed out first before any real impact was made on the wheel i think. Though i guess i could just do a few revs of the wheel then take it off and polish it with the dremenal.

[marki]

Originally Posted by 2stroke

Was thinking of that but the worm is brass and the wheel some kinda of alloy mix. If i did the brass worm would be chewed out first before any real impact was made on the wheel i think. Though i guess i could just do a few revs of the wheel then take it off and polish it with the dremenal.

PE is the result of flex and slop in the machine and tools used to cut the thread and will therefore remain a feature of the worm no matter what you do short of machining off the original threads and re-cutting them on a blank surface. Materials and grains in the metal used to make the worms will also play a part in this. Lapping would not correct PE inherent in the worm but if done carefully should knock off some of the lumps and smoothen it somewhat. The rest could then be managed with auto guiding as you have no chance if there are large random spikes. You would not need to cut so deep as to force severe wear on the worm or wheel as this would worsen the problem with backlash. I imagine setting the clearances carefully whilst the worm and wheel are in place on the mount and using a drill at low speed with some very fine diamond grit for about 5 full rotations of the wheel would do all you could to improve the situation. Take the mount apart and give it a very good clean up then regrease all the bits and see what happens. You would of course need to have done a PE run with PEMPro or similar first so you could compare before and after.

Mark