Vertex Dividing-Head – basic help please

[Anonymous]

While I have a full set of change wheels and the banjo I don't have the expanding arbor that fits in the back of the spindle (the late JohnS couldn't find it). So it was easier to make a division plate as I already had an offcut of aluminium of the correct size and thickness. The holes were drilled using the bolt function on the DRO.

Andrew

[BazyleParticipant @bazyle]

Posted by not done it yet on 04/01/2021 09:57:40:

What is it with people and simple maths!

Take a somewhat simplified example.

Say 1). the table turns is 90 per full revolution

2). Ten teeth are required.

Very clearly the answer will be 10 turns per tooth, but lets do the calculation, just as a demonstration….

……………………………

eh? is there a version of this in English?

I think there were lots of reasons not just lack of calculators that drove the likes of B&S and Elliott and Machinery Handbook to issue tables that even us mathematically challenged could look up division rations in. These can be found on the 'net aswell as the table in the link given by MG for the Vertex earlier.

The standard set of 3 plates fro B&S had 18 circles of holes and Elliott 23 I think. However both offered extra plates with more primes, inclucing 63, but of course these are rare on the used market. Odd that I'm not immediately seeing such extras for the BS0 clones.

BTW it is always worth checking if your maths is up to it. The Elliott table for differential indexing 201 divisions is wrong – but I doubt anyone has ever wanted to make a 201 tooth gear.

[HopperParticipant @hopper]

Ah, the joys of having a GH Thomas Versatile Dividing head with the extra fine adjustment that allows you to advance the index plate itself by a measured extra amount for doing primes etc.

I wonder if its possible to set up a similar thing on these commercial units? Its a simple 60T wormwheel and worm with a micrometer dial. But it means mounting the indexplate on a moveable hub.

Seen in use here with a single row of 60 holes used with the fine adjustment to make all the remaining circles of holes for a set of three indexing plates. Accurate to within one thousandth of a degree according to George.

[not done it yetParticipant @notdoneityet]

with more primes, inclucing 63,

Just to keep the record straight (for the non-maths types). 63, having factors (other than 1 and itself) is not a prime number.

If a particular dividing head, such as a 40 turn item, needs a plate with the exact number of holes that does not make that number a prime.

[BazyleParticipant @bazyle]

Indeed, a slip on my part but obviously it is an useful number. Out of interest the extra plates provided by Elliott are as follows and ot all primes:

53	57	59
63	67	69
73	77	79
83	87	89
93	97	99

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