Well as some of you will know I'm computerising my 10" EQ mounted Newt. Well half way through I realised that I needed a worm and wheel for the Dec axis, I did try to find one on the web, but I was not very successful, so I decided to look into making one myself.

At first I was going to make one out of plywood and JB-weld or similar product. As the idea grew I decided to try hobbing one out of aluminum, which if it didn't work would be the wheel onto which the metalized epoxy would be applied. As it happened all went well and I now have a 188 tooth wheel which meshes with 3/8-16 threaded rod.

Here is how I did it.

Step one.



The first thing to do was to cast a blank for this gear, that done I removed the stainless steel core that I used to form the rather clean hole seen in the center. This core was then re-inserted and the wheel machined to size using it as an arbor.

Step two.(A false start)



As you can see from the photo I first tried to use a tap and the hob, this did not work as the threaded portion was too short in relation to the gaps.

Step three.



Having made the discovery that a tap would not work I decided to use the worm I had made as the hob, to this end I filled a spiral groove into it and used it successfully. One thing I should mention at this point is that I had to turn the lathe by hand through out the whole operation.

Here is what the lathe looks like set up to hob a worm-wheel.



You will note that the primary drive belt has been removed for ease of hand turning.



Here is a close up of the setup, you can see the hob held in the drill chuck which is in turn held but my three jaw chuck. This was done to give adequate clearance between the chuck and the wheel blank. The 1" OD post on the top slide is the axel that the wheel turns on while being hobbed, please note the judicious use of washers to give the required center hight. The wheel axel has to be perpendicular to the top slide, other wise the helix angle will be out and the wheel won't work well.

Here is the finished wheel.



For scale the surface it is sitting on is the ways for my home built lathe which is 1/4" thick.

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