A1-8 to D1-6 Chuck/Spindle Adapter

I came across a nice Rohm 12-inch independent 4-jaw chuck with integral A1-8 mounting taper and holes.

My Monarch 16 CY has a D1-6 spindle.

I had the idea to turn an adapter as pictured below to use a spare D1-6 mounting plate to mount the 4-jaw chuck.

The adapter would fit the ID of the straight bore going through the D1-6 mounting plate and will fit the A1-8 taper on the 4-jaw chuck. The chuck will be attached to the backing plate with bolts with the adapter sandwiched between the chuck and backing plate.


Seems like a straight forward solution but since I couldn't find any such animal commercially available I wonder if I'm missing something. Any reason this wouldn't work? If it makes any difference, the chuck and lathe don't see any heavy duty work anymore.





Full resolution pictures here:
4-Jaw - Google Drive

Why not use the taper on the chuck as the locating hole for the pilot on the adapter, then use the A1-8 holes for attaching the d1-6 adapter? Eliminate the middle part.
Mount the adaptor you have, face cut it 1/8" or more deep leaving the pilot with angled edges to center on the -8 hole in the chuck. The pilot does not need to be the full depth of the recess in the chuck.

Rob F. said:

Why not use the taper on the chuck as the locating hole for the pilot on the adapter, then use the A1-8 holes for attaching the d1-6 adapter? Eliminate the middle part.
Mount the adaptor you have, face cut it 1/8" or more deep leaving the pilot with angled edges to center on the -8 hole in the chuck. The pilot does not need to be the full depth of the recess in the chuck.

Click to expand...

That was my initial idea too, but I dismissed it because the pilot on the adapter would intersect the camlock studs on my adapter plate.

Kind of depends - is the A8 attaching bolt circle 4 3/8 or 6 3/4 ?

Former easy to interfere with D1-6 features, latter not so much

Do note the D1-6" not only has cam pins on a 5 1/4 B.C. - but also lock screws for those cam pins beside them

Ref ASA/ASME B5.9 Spindle Noses

johnoder said:

Kind of depends - is the A8 attaching bolt circle 4 3/8 or 6 3/4 ?

Former easy to interfere with D1-6 features, latter not so much

Do note the D1-6" not only has cam pins on a 5 1/4 B.C. - but also lock screws for those cam pins beside them

Ref ASA/ASME B5.9 Spindle Noses

Click to expand...

The A8 has a 6 3/4 bolt circle.

I should have in the neighborhood of 0.3" tangent to tangent clearance between the A8 mounting bolts and the D1-6 studs in the worst case based on my conceptual model.

*D'B=6bk said:

That was my initial idea too, but I dismissed it because the pilot on the adapter would intersect the camlock studs on my adapter plate.

Click to expand...

I see, Can you make the center piece a press or shrink fit into the D1-6 plate, no possibility of loose part causing a problem. Are you planning to just press in the center blank and turn the taper to size, and face it in the lathe?

Rob F. said:

I see, Can you make the center piece a press or shrink fit into the D1-6 plate, no possibility of loose part causing a problem. Are you planning to just press in the center blank and turn the taper to size, and face it in the lathe?

Click to expand...

Yes, that is basically the idea I had.

johnoder said:

Kind of depends - is the A8 attaching bolt circle 4 3/8 or 6 3/4 ?

Former easy to interfere with D1-6 features, latter not so much

Do note the D1-6" not only has cam pins on a 5 1/4 B.C. - but also lock screws for those cam pins beside them

Ref ASA/ASME B5.9 Spindle Noses

Click to expand...

Does ASA/ASME B5.9 give the depth that the studs should thread into the backing plate for a D1-6?

I took a closer look at my plate and I could possibly trim about 1/8 off the threaded end of the studs and turn a pilot as Rob F. suggested.