On Fri, Mar 31, 2023 at 10:28 PM, Bill in OKC too wrote:
There is enough metal there you could skim off much of the back of the chuck, and make a? back plate for it, too.?
Apart from the fact that you don't need absolute concentricity with a four jaw, since, as already noted, the whole point is that you can adjust for any eccentricity, the original Unimat chucks didn't have a back plate and ran very true. Also, if you want to machine it for a back plate then you have to be able to mount the chuck very accurately to make sure the recess you cut is precisely concentric with the cuck body. To do this you would need to set it up in a four jaw chuck - but that's the one you want to machine!
The obsession with backplates should be ignored. My most accurate 3 jaw chuck, on my U3, gives a runout of half a thou (0.0005", about 0.01 mm) and has no backplate. My ER16 & 25 collet holders are better than that, and do not have back plates. There's this thing called precision. It deals with the problems.
