Finally (after only a year or so of work,) got the fabricated Versatile Dividing Head to the GH Thomas design to the point where it can be used to drill the holes in its own indexing disks — to a theoretical accuracy of 1,000th of a degree no less!
Trick is to drill the first of three index plates so it has one circle of 60 holes. I shorcutted GHT's suggested method by using my own addition to his design, a plunger that directly engages with the 60T "wormwheel" gear to give 60 divisions.

Then the disk with the 60 hole circle is transferred on to the indexing attachment and from this we can index all the rest of the hole circles on all three disks.

This is done by using the facility of one full turn of the handle equals one tooth on the wormwheel, or 6 degrees, therefore each of the 60 holes in the circle equals one 60th of that, or one tenth of a degree. To get closer to our goal we then GHT's cunning Micro Adjustment Attachment, which reads off in one thousandths of a degree.

It does this by engaging a worm with another 60T wormwheel on the back of the indexing disk holder, thus rotating the disck itself by one 60th of a turn for each full turn of the knob, which is graduated into one hundred graduations. This advances the disk that little extra bit, which takes the handle with it and thus advances the main spindle by that tiny amount.

Paintstaking work, with each movement requiring the counting of handle turns, then the use of the sector fingers to add so many holes, then the rotation of the micro adjust dial to add the few extra thousandths of a degree. GHT says he took about 20 seconds per hole. I don't know how. It takes me 30 seconds just to make the above adjustment to the indexing set up, then another 30 seconds to drill the hole itself. Plus with a bit of faffing about, about 40 minutes to drill a circle of 30-something holes. All up there are about 850 holes to drill in the three plates, so a minimum of 14 hours of work!!!
At least GHT did all the math and laid out charts of how many turns, holes and micro adjustment settings for each hole in each circle (he really was a terror!) so all I have to do is keep track of where I am at.

Then when I get done drilling all 850 or so holes, I get to deburr each one, both sides with a tiny chamfer. I can hardly wait.
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