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Dividing head advice

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SillyOldDuffer15/04/2022 09:22:16
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8857 forum posts
1994 photos
Posted by Michael Gilligan on 15/04/2022 08:26:40:

Posted by DC31k on 15/04/2022 07:25:47:

.

John Hinkley provides reasoning for a 90:1 ratio. I tend to agree with him.

.

dont know

John’s reasoning seems incontrovertible

… except that there are only 240 divisions around the plate.

He does have the right answer though !

MichaelG.

Edited By Michael Gilligan on 15/04/2022 08:52:23

Except I jumped to the conclusion it was 60:1! Given my impressive track record of mistooks, the first thing I'd do is confirm the ratio on the actual device by counting the number of handle turns needed to rotate the head once. Always good to nail facts rather than join dots!

I fear it won't be possible to identify the make and model of Robert's dividing head or to find spares for it. Many firms could have made it, some of them with tiny production runs.

As making and using division plates is a pain in the rear end, especially if the number of holes have to be calculated and drilled from first principles, I repeat my suggestion of driving the head with an Arduino and stepper motor instead. Doesn't require the operator to look anything up in a table or keep count and the head can be moved to any angle within the accuracy of the stepper and worm, not needing the differential gear fitted to posh dividing heads to produce angles ordinary hole plates can't do.

Dave

John Hinkley15/04/2022 09:25:21
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1352 forum posts
430 photos

Michael,

You're quite right, of course. My observation of 360 divisions is wrong. What I should have said was that there are 240 divisions - 4 sections of 60 divisions each, with supplementary engravings at the 1, 2 and 3 degree points. That is 4 degrees per handle revolution. 4 degrees x 90 handle turns = 360 degrees. QED as we used to say.

That'll teach me not to "show my workings"! Maybe.

John

Howard Lewis15/04/2022 09:28:17
6295 forum posts
15 photos

IF the ratio IS 90:1, having one Division Plate, by reference to the HV6 chart, another plate could be made carrying some of the hole circles missing from the existing plate. (Ideally, using the iterative system of using a "mule" plate to reduce the errors on a second)

In this way successive plates could be made to extend the number of divisions available.

The three plates supplied for the HV6 do not cover all the possibilities between 1 and 100.

One day, I'll get round to making up one or more plates to cover some of the blanks. But even then, there will still be some,

Howard

Michael Gilligan15/04/2022 09:39:44
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20289 forum posts
1064 photos

Now … as we’re all trying to do some ‘reverse engineering’ can we please agree that the worm:wheel reduction ratio is actually 1:40

33f46973-8a1e-41c2-9396-292199cc60a7.jpeg

.

Cropped from a photo in Robert’s Album, in which the single-start worm is also visible

angel MichaelG.

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