Dividing head for Tom Senior Mill advice

I think Andrew meant make a 59 hole plate as that's an easier number to fit onto a blank than 118. I believe Old mart has a DRO so should not be a problem to come up with any number of holes on a disc provided they fit.

Difficult to give an exact height when a div head is vertical with chuck as it will depend somewhat on the size of chuck being used and a threaded body one will result in a lower overall height than one on a threaded backplate.

I have the 3 dividing plates for the 6" RT's but lacking the 59 hole and for one probably never to be repeated scale (3mm pitch leadscrew on an imperial lathe cross slide, hence the 118 divisions) it would not be worth it. And how could you make one if you only had a dividing head?

It was meant to be serious. My bad for mentioning engineering on a modelling forum.

I made the assumption that if "old mart" had a 59 hole plate available he would have had the wit to use it. Assuming a 40:1 dividing head the indexing needed at each step is 40/118, times 9 to the get the answer in degrees. One can use the prime factorisation theorem to simplify to 20/59.

The easiest way to make the plate is using a DRO with a bolt function, which is what i did. But there are other methods which do not need a DRO - see one of the Bedside Readers, can't remember which volume. Any errors in the radial placement of the holes will be reduced by a factor ot 40.

Andrew

I have the reference charts for all the dividing plates which came with the RT (3), and when looking for 118, was surprised just how many numbers were missing. This would not affect many people who are quite happy with the 24 positions common to most dividing heads, which give 2, 3, 4, 6, 8, 12 and 24 equally spaced positions before resorting to the dividing plates.

I measured the height of the 6" RT with a 5" Pratt Burnerd chuck and the 6" lightweight independent, and forgot to bring the figures home with me. I believe the PB was 142mm to the end of the jaws, the independent would be about 5mm less. With hindsight, I would have gone for the 3 tee slot top rather than the 4 slot, because it would be easy to fit a three jaw scroll with front mounts which gets used more often on the RT. To hold the 3 jaw scroll on the top, I drilled and tapped 3 mounting holes in 8mm with just enough clearance in the chuck holes to get the chuck on centre before tightening them. For quick centring to +- 0.001" I just stick a test bar down the MT2 centre bore and gently clamp the jaws on it.