Myford ML7

Can I fit a 4" back plate to a 6" chuck?

Probably not but it will depend on the bolt PCD of the chuck, in most cases the bolts on a 6" chuck will fall outside a 4" backplate.

J

Malcolm,

If you mean the backplate from a 4" 3-jaw to a 6" 4-jaw, then definitely no. The registers are different and a 3-jaw usually has 3 bolts whereas a 4-jaw has 4 bolts. (As fitted to Myfords)

If they are both 3-jaw or 4-jaw then Jason's "probably not" applies.

Can you actually fit a 6" chuck to an ML7? Unless it's very short I would have thought the jaws would strike the bed if they are opened very much (and if you can't open the jaws wide, is there any point in using a chuck that big?).

Not a lot of room it's true, but if you want to face off a bit of 4" square on the lathe, then that's the way to do it as Mr Punch used to say.

I think most chucks are fitted to backplates so that the mating faces are the ones with the through bolt holes. On 3 jaw chucks, because of the scroll mechanism, the bolts pass through the periphery but on 4 jaw independent chucks the bolt holes are generally nearer the centre so the backplate can be smaller - as on the 4" 4 jaw in the pictures below.

So I guess there is a chance that you can fit a 6" on a 4" backplate. However, there is still the issue mentioned above by OMG. The Myford 6" 4 jaw is especially thin with the screw and register machined into the chuck body - there is no backplate so the whole thing fits in the gap. The 4" will hold a piece of 4" square with the jaws turned round .

HTH

Rod