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1 1/2 inch Allchin

Wormwheel missing

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Gerry Walster24/05/2018 12:41:57
7 forum posts

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

JasonB24/05/2018 13:42:13
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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.

Gerry Walster24/05/2018 14:10:18
7 forum posts

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

Clive Brown 124/05/2018 14:31:12
168 forum posts
5 photos

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.

Gerry Walster24/05/2018 16:43:25
7 forum posts

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

JasonB24/05/2018 17:40:33
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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

Gerry Walster24/05/2018 18:41:27
7 forum posts

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

JasonB24/05/2018 18:49:31
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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.

Gerry Walster24/05/2018 19:00:18
7 forum posts

Clever guy, and a simple solution.

Andrew Johnston24/05/2018 21:54:45
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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:

governor pulley pinned.jpg

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:

worm wheel gashing.jpg

followed by free hobbing is best:

worm wheel hobbing.jpg

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

worms and worm gears.jpg

Andrew

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

Gerry Walster24/05/2018 22:06:16
7 forum posts

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.

JasonB25/05/2018 07:02:03
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This photo of Andrews shows what the cutter should look like.

Gerry Walster25/05/2018 10:02:23
7 forum posts

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

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