Thread: Setting dividers for a PCD

That is the trouble as we ALL get older our eyes get bad. Try using an optical enhancer, I have seen in Model Engineers Workshop, where you can make one yourself. It is basically a base that has a clear rod with a cross marked on the bottom. Once on the intersection, a punch is installed when the rod is taken out and then hit with a hammer. Look under a magnifying lens to set up your calipers, might help to see where the points are in relation to the pads of the micrometer.
Failing that use a pair of digital calipers to mark the PCD.
Kryn

Hi Michael,
Try a set of trammells.

Phil

Any reason why it wasnt done on a dividing head or rotary table.

I'm trying to make an adaptor that I can attach to a R/T or D/H so that I can mount a chuck with things like this in it. At the moment I haven't got a way of securing the billet to the R/T without clamps etc getting in the way. (Cylinder 92mm diameter, 60mm high). So, once I have the adaptor made I'll be doing this sort of job on the R/T. Until then...

I have used digital calipers before for this sort of thing but because of the non-symmetrical nature of a caliper blade, I'm not sure that they wouldn't cam out of a punch mark as well.

For a radius of 1.391", I'm not sure my trammels would be any better and would certainly be more cumbersome. My trammels have a beam of something like 20" on them. For this job I was using a 3" set of dividers - I would have thought the ideal size for the radius involved.

I could mount this on the mill or on a small X-Y table I use on the drill press and convert the polar coordinates to X-Y, but apart from needing to keep to within a whisker of nominal it should be a straight forward job.

Michael

Hi Michael,
I think I made the same thing awhile back. There is a thread on it but I can't find it as I am on my phone atm. from memory I used a r/table rather than pcd. You have to come up with a way to bolt it to the table sooner or later.
Stuart

This one? https://www.woodworkforums.com/f65/ro...estons-133374/. (BTW the search feature sucks. I entered the exact title and it didn't come up. )

I did some searching on the internet and discovered one source that said effectively that on a good day with the wind from the right quarter you can get within 6 thou using dividers. As I was trying to achieve a geometric tolerance of 2 thou, no wonder I was not getting what I wanted (and the wind was all over the place too).
I eventually used the R/T with strap clamps and maneuvered the drill bit around them . It was an ugly set up as the divisions on my mill are 0.05mm, so I used a stack of gauge blocks and a dial indicator to give me the necessary offset. If I do that again I should think about a better way of attaching a dial indicator to the mill that will not move as much - that was probably the main contribution to the error I eventually ended up with. (Get a DRO? that's crazy talk!)
Everything else went smoothly until I got to the final step - turning the locating taper. While I managed I was certainly cursing the person who decided to dimension the taper to a virtual sharp corner with a tolerance of plus nothing minus 5/10ths .
That's the chuck part done. Now for the spindle part...

Michael