1 1/2 inch Allchin

desperate for advice on obtaining the original style wormwheel. 1 3/16 diameter, 20 teeth with 5/16 diameter bore. Can’t locate a stock item or manufacturer. I still have the original worm. Any help or advice would be appreciated. Gerry

Not sure if one was ever available but Reeves may have done them at one time. The book and build articles describe the method to hob one yourself.

Thanks for your response. Reeves have a modified version, completely different from the original design. I’m trying to maintain the model as original.

My Allchin has the Reeves worm and wheel, purchased decades ago. It's a 4 start worm, so rather unusual and doesn't look very prototypical. Neither does its matching wheel, but the high ratio gives quicker steering response which might be an advantage. Both items needed machining after purchase to fit the shafts.

TBH, if I were replacing the pair for better appearance I would look at the KHK Gears web-site or have a go at hobbing, as JasonB suggests.

Interesting. I think I may have to modify for a new fit. I don’t have the capability to hob. Thanks for the advice.

If you have a screw cutting lathe it is not too difficult. Basically you make an overlong worm from steel, cut off the end to use as your actual worm and the bit that remains on the bar has some straight flutes cut into it much like a tap and then case harden it.

The blank wheel is mounted horizontally and fed into the revolving cutter much like this

Edited By JasonB on 24/05/2018 17:41:21

Jason, I would never have considered your method. What a great idea, and I will give a go. Many thanks.

It's the way Bill Hughes suggested doing it in his original article. He does suggest gashing first which is simply cutting 20 shallow slots on the wheel at 75degrees equally spaced. This helps the wheel to start turning rather than risk the tap acting like a roughing mill and just eating a chunk out of the wheel in one place.

Clever guy, and a simple solution.

The tap method works well, but it is rather hit 'n' miss as to the number of teeth you get if the worm wheel isn't gashed first. That may, or may not, be an issue depending upon the application. It wasn't an issue in this case, only the axis to axis distance was important:

Using a spiral flute tap (as shown in the video) is also helpful, as there is always at least one tooth driving the worm wheel.

If the number of teeth is important then gashing:

followed by free hobbing is best:

Giving a worm wheel with the correct number of teeth, and the correct tooth shape:

Andrew

Edited By Andrew Johnston on 24/05/2018 21:55:09

A Very professional finish achieved. Wish it was that easy because the wormwheel I need has 20 teeth and a diameter of 1 3/16 inch.

This photo of Andrews shows what the cutter should look like.

Interesting tooling and techniques, very much appreciate the positive responses that come through this forum.