Chuck Back Plate - What To Register?

Jim Frame · Jun 19, 2018

I acquired a chuck with a D1-5 back, but my lathe has a 2-1/4"x8 threaded spindle. I plan to remove the cam studs and machine a back plate for it, using the cam stud holes for attachment. I'm wondering if it would be better to turn the plate to fit the inner tapered recess, the outer plain recess, or both. (If it isn't obvious, I'm pretty green at lathe operations, but this *seems* like a straightforward project.)

Suggestions?

Thanks!

L Vanice · Jun 19, 2018

The chuck was made to register radially on the short taper, so the obvious solution is to make the adapter to suit that feature. The resulting accuracy will mostly depend upon how well you fit the adapter to your lathe spindle and how well the chuck was made.

Larry

johnoder · Jun 19, 2018

Handy info standard on USA built D1-5" is 4.125 B.C. for studs and 1/2-20 tapped holes for them. This is a good size c'bore in the back plate for socket head cap screws

EPAIII · Jun 19, 2018

Unless I am mistaken, that is a four jaw chuck - a four jaw, independent chuck. So the work is centered in the jaws each time anything is mounted in it. The centering of the chuck on the spindle is not that critical and it can be off by a few thousandths with no ill effects. It would be more important to get the axis of the chuck parallel to the axis of the lathe spindle. So be sure the mating faces of the adapter are perpendicular to the axis and don't worry too much about the centering. I would face the adopter as a last step while it is mounted on your lathe spindle to get the best results. Then mount your chuck on it, remove the jaws, and check for any deviation from a zero reading on the face of the chuck.

Jim Frame said:
I acquired a chuck with a D1-5 back, but my lathe has a 2-1/4"x8 threaded spindle. I plan to remove the cam studs and machine a back plate for it, using the cam stud holes for attachment. I'm wondering if it would be better to turn the plate to fit the inner tapered recess, the outer plain recess, or both. (If it isn't obvious, I'm pretty green at lathe operations, but this *seems* like a straightforward project.)

Suggestions?

Thanks!

Jim Frame · Jun 20, 2018

1/2-20 tapped holes for them. This is a good size c'bore in the back plate for socket head cap screws

"Good size" as in "Hey, that's a really nice size," or as in "Whoa, that's way too big!"? It's a Polish Bison, and the cam lugs are threaded M12-1.25 (I think), so close to 1/2-20.

Jim Frame · Jun 20, 2018

EPAIII said:
Unless I am mistaken, that is a four jaw chuck - a four jaw, independent chuck. So the work is centered in the jaws each time anything is mounted in it. The centering of the chuck on the spindle is not that critical and it can be off by a few thousandths with no ill effects. It would be more important to get the axis of the chuck parallel to the axis of the lathe spindle. So be sure the mating faces of the adapter are perpendicular to the axis and don't worry too much about the centering. I would face the adopter as a last step while it is mounted on your lathe spindle to get the best results. Then mount your chuck on it, remove the jaws, and check for any deviation from a zero reading on the face of the chuck.

Yes, it's a 4-jaw independent. Thanks for the tips!

Jim Frame · Jun 20, 2018

the cam lugs are threaded M12-1.25 (I think)

I thought wrong: I just measured one, and they're M12-1.00.

But it occurs to me that if I get a back plate with a pronounced hub (i.e. the major diameter of the plate is set forward of the portion that threads onto the spindle) I won't have to counterbore the capscrews at all, as there'll be plenty of clearance between the back side of the plate and the headstock casting.

Like this (not my lathe, just a photo I grabbed off the web):

crossthread · Jun 20, 2018

That looks like a lot of unnecessary overhang to me.

Jim Frame · Jun 20, 2018

crossthread said:
That looks like a lot of unnecessary overhang to me.

To me, too. That was just to illustrate the concept, and was the first photo I came across.

The back plate shown below is more like what I'd be aiming at. I'm not averse to counterboring, but since an M12 capscrew has a pretty tall head I may have to leave some of it protruding in order to leave enough material below the cap to support the chuck.

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Chuck Back Plate - What To Register?

Jim Frame

Plastic

L Vanice

Diamond

johnoder

Diamond

EPAIII

Diamond

Jim Frame

Plastic

Jim Frame

Plastic

Jim Frame

Plastic

crossthread

Titanium

Jim Frame

Plastic

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