Making an adapter plate for 3-jaw chuck

cfellows · Oct 6, 2011

Locating and drilling bolt holes on a circle of a specific diameter has been a bit of a black art for me that I never mastered. So, when it came to making an adapter plate for my new 4", 3-jaw chuck I decided to do it the easy way. I turned a chuck with existing holes upside down and clamped the self centering jaws onto a center pin in my rotary table. Then I simply moved the milling table over until a screw chucked in the drill chuck exactly lined up with one of the threaded holes in the back of the chuck.

Then I removed the chuck from the rotary table and clamped the adapter plate to the rotary table, centered on the same pin used to center the chuck. Put a center drill in the mill and proceeded to spot, then drill the holes using the rotary table to index the proper position on the bolt circle.

Chuck

I did the same thing for the outer ring of holes used to bolt the larger, 4 inch chuck to the adapter plate. I know this won't teach anyone the proper way to locate holes but it worked for me.

mzetati · Oct 6, 2011

Chuck,

sure, it works: as well as the workpiece is well centred on the RT.
What I'm usually doing is zeroing the DRO somewhere on a piece of scrap clamped on the table, then machining a close fitting fixture for the workpiece on the mill itself, and finally drilling at coordinates.

Thank You for the tip.
Marcello

cfellows · Oct 7, 2011

Finished up the adapter plate and mounted it on my lathe.

The holes for the mounting bolts are bored about .030 oversize. Since this chuck will be adjustable for runout, the holes had to be made larger to allow for movement.

Here's a picture of the ring that will hold the adjustment set screws. The ring is bored out to about .004" smaller than the chuck so it can be heated and shrink fitted onto the chuck. The adapter plate is about .030" smaller in diameter than the ID of the ring, again, to allow for movement.

And here's the chuck fitted to the lathe. You can see the 1/4" x 20 set screws around the periphery of the ring. There are 4, equally spaced around the ring, to provide radial adjustment. This allowed me to get the runout to under .001".

Someday I'll need to take a finish cut across the OD of that ring to get rid of the rust and pretty it up!

Chuck

Harold Lee · Oct 7, 2011

Chuck,

Looking at you last picture I see you have a carriage stop. I have a 7X14 and would like to make one for my lathe. Do you have a drawing in it? Could you post some pictures of it?

Thanks,

Harold

cfellows · Oct 7, 2011

Harold Lee said:
Chuck,

Looking at you last picture I see you have a carriage stop. I have a 7X14 and would like to make one for my lathe. Do you have a drawing in it? Could you post some pictures of it?

Thanks,

Harold

Here's a drawing. Let me know if you have any questions.

Chuck

MachineTom · Oct 8, 2011

There are simple formula's for bolt circle heres the one for three holes.

PD= bolt circle diameter

find center,draw x-y axis, assume one hole at 12:00, on diameter,

holes 2 and 3 will be .2500*PD below center X axis, and .43301* PD from Y axis, The distance between any 2 holes will be .86603*PD

Since most times you don't know the bolt circle diameter, measure between two holes with a caliper, add the diameter of the bolt hole, Divide that # by .86603 and the result will be the bolt circle diameter. This is only for three holes.