Back plate for a 6-inch 4-jaw Chuck

My PM-1640 lathe came with a 12-inch 4-jaw chuck that is larger than what I need for many jaws. I acquired a smaller 6-inch 4chuck and decided to make a D1-6 back plate for it. Obviously, I could have just bought one, but part of the reason for having a hobby machine shop is to allow making things myself.

Turning the back plate - initial Steps

My first step was to turn one side of the back plate, boring the center hole, and turning an indicating surface on the periphery.

The cast iron disc that I started with had been sawn from a round,
so my first step was to face a flat surface. There was no need to
go all the way to the center.

Next, and not shown, I turned an indicating surface on the periphery.
I then drilled a pilot hole in the center.


Enlarging the center hole.

Boring the center hole to size, matching the chuck's hole.


I did a layout for six holes around the plate's periphery,
and then drilled these on my drill press (not shown).
I used these holes to mount the plate on a rotary table,
using the indicating surface turned earlier to center the plate.

Drilling holes the for the studs.


Tapping the stud holes.

Boring the relief holes for the studs


Drilling the holes for the cap screws that lock the studs in place

Tapping the stud holes.
The spindle side of the back plate is now complete.


Making the studs

The D1-6 camlock system uses 7/8-inch studs. I made mine from some 4140 alloy steel rounds. My rounds were rather rusty, but the outer finish on the studs is not critical. After cutting the pieces to length. I cleaned them in a vibratory tumbler before taking them to the lathe.

I faced one end of each stud, and then turned it end-for-end.
I used a parallel to seat each piece to the same depth in the chuck,
and then faced each to length.

I then cut the thread surface to diameter.
I needed to be careful because heavy cuts would push the stud
into the chuck. My next project was to make a stop to fit the chuck!


I made a jig to hold the studs in the B&S vise on my Cincinnati mill.
The mill stop aligns the jig, and the line on the jig aligns the stud.

Milling the cam surface in the stud using a
form-relieved convex milling cutter.


Milling the clearance groove for the cap screw that locks the stud in place.


Putting it all together

After threading the studs into the back plate, I performed the iterations needed to adjust each stud to the proper length. Once these were set, I was able to mount the back plate on the lathe for final finishing. This ensured that the chuck would be aligned properly with the spindle.

First, I rough faced the disc, and then turned the periphery down to the diameter of the spindle.
The 0.250" depth of cut was no problem for the PM-1640.


I used a round-nose HSS bit for the heavy interrupted cut.
Carbine inserts might have chipped.

Turning the final outside diameter removed the six
holes previous used to mount the disc on the rotary table.


Turning the face that fits the chuck back,
leaving a central boss to align with a recess in the rear of the chuck.

The chuck mounts to the back plate with four cap screws.
I transfer punched their location, drilled the holes on the G3617,
and then tapped the holes by hand.


The finished product.