Making worm wheels

[AjohnwParticipant @ajohnw51620]

This cropped up some where recently, Might not have been on here however a pretty good video on the process

https://www.youtube.com/watch?v=-umcQtrn1CQ

Where ever it cropped up some one hack sawed the slots needed in the wheel before cutting it by eye.

They can be lapped and polished afterwards with another worm. Astro people don't seem to appreciate the advantages of huge worm wheels with lots of teeth. Dividing heads etc do. If perfect they reduce the error in what ever is rotating them by their ratio. When they have an error things aren't that simple but given the way they are produced they tend to be pretty accurate anyway.

John

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[AjohnwParticipant @ajohnw51620]

Worm wheels and worms

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Ajohnw on 21/01/2016 23:53:10:

Astro people don't seem to appreciate the advantages of huge worm wheels with lots of teeth.

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… Really

**LINK**

… I suppose it depends how you choose to define 'Astro people'.

MichaelG.

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Edit: If you are interested in making a WormWheel, have a look at these old notes by Chris Heapy.

Edited By Michael Gilligan on 22/01/2016 07:02:45

[john carruthersParticipant @johncarruthers46255]

Bigger is better, the 28" at Greenwich has an RA wheel 5' in diameter.

Mass produced mounts use smaller wheels just to keep price down.

This is a common method of cutting a wheel, pre gashed and using the worm as the hob.

http://www.mini-lathe.org.uk/making-telescope-worm-wheels-gears-mini-lathe.shtml

[Neil WyattModerator @neilwyatt]

I'm not convinced pre-gashing and hobbing is accurate enough – the wheel I made that way in my rotary table is not accurate enough. I'm going to make another one and get it cut on a CNC hobbing machine.

Neil

[AjohnwParticipant @ajohnw51620]

There is a rage on tooth belt drives Michael Even a claim that they even out tooth error and don't stretch etc and can be used up to 10,000 rpm so must be wonderful. Really the base problem is the number and size of gears that are used up to the final axis drive. They tend to be rather small early on so rotate at pretty high rates in terms of astro photography exposure times so the slightest wobble causes drift. People with good technique and autoguiding still produce amazing results with them. Some spend more and more on mounts. Some stick with exposures that are as long as possible. People also get good results without even doing that particularly with dslr's.

The old rule on ideal worms wheels was diameter >= the diameter of the scope being used.

Neil, many have made them with a fair degree of accuracy, allowing them to rotate freely as they are cut seems to be the key and that goes back to pre wwii. At some point I will try a trapezoidal tap with a good tapered lead in which should get round initial engagement problems. Old advice using home made hobs was to wind in quickly. A metric tap as they are cheaper from china than acme usually is.

I own a mount by Meade that Astrophysics used to work on and rebadge – they did 2 main things. Lapped the worm and changed the goto software. Also mounted it on a hefty pier. Considering what is around now I decided to stay with it for if I need a mount this substantial. People are locked into tripods too. Any one who has owned a Vixen GP pier would realise that they are light portable and very stable. In fact I reckon they are quicker to set up too. Trying to get the top of a tripod dead level is a real pain.

John

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