How to Make Cole (Jumbo) Jaws for Lathe

by Mark Kauder, Phenix City, AL

Last Week in a thread about lathe chucks, I mentioned to Butch Collins that I made my own Cole Jaws (Jumbo Jaws) for my Supernova chuck. I told him that I would post a how to. I made mine from ½" Birch Plywood, but you can use most any material. My first set was made of clear Plexiglas it worked OK, until I accidentally hit it with a tool, and it broke. I glued it back together (twice), but it was never quite right after that. Phenolic or aluminum would be great. My wooden version does not require anything but woodworking tools to fashion it. Forgive me, but I did not take pictures when I made it, so I do not have pictures of all the steps.

I have a Jet Mini-Lathe with a maximum of 10" swing over the bed. As such, that is the limit for my Cole Jaws.
Determine the difference between the fully closed and fully open jaws size on your chuck. Mine is 7/8". Subtract that amount (plus a small safety factor) from the maximum swing. For me that was 9".

I cut a 10" square of ½" Birch Plywood, found the center.

I then took the regular jaws off of my Supernova, and arranged them on the plywood so that I could accurately mark the screw holes.
Drill and countersink the holes for the screws that attach the jaws to the chuck. In the case of mine, I used the same screws that hold the standard jaws. Be careful that you get enough of the screw out the other side to securely fasten it to the chuck – at least two full threads. I intend to get longer screws in the near future. Also make sure that you do not set the screws so deep, that you do not leave enough wood to hold the jaws.

Now, mark and cut the circumference of the Cole Jaw using a band or jig saw. DO NOT divide it up into quarters yet.
Attach the board to the jaws, making sure all your screws line up (adjust as necessary). Mount it on your lathe, and turn it round. Radius the front and back edges slightly, and sand smooth.
While on the lathe, starting at the outermost mounting screw hole, mark concentric circles every ½" all the way out to the edge. Mark first with a pencil, and then etch in the lines with a point tool, or the point of a parting tool. Don't go too deep, just enough to leave a permanent line. Sand the front smooth.
Now mark each quadrant, as seen as the dark lines in the photo. Each line is 22.5 degrees from the other. You will end up with 8 equally space lines – avoiding the lines that you will soon cut (pencil lines in the photo).

Drill a hole at the intersection of each of the 8 "Button" lines (do not include the lines that you will cut later) . If you are using Metal or plastic, us the appropriate drill size for the tap that you will use to thread the hole. If using wood, pre-drill for the size wood screw that you will use – this eliminates the splintering that you would encounter if you would just screw directly into the wood.
Once the holes are drilled, you can it into quadrants cut along the pencil lines. When you do, mark each quadrant so that you can keep them in the same order all the time, and attach them to the same jaw on the chuck each time.
I bought the rubber "Buttons" that I use to hold the work piece at Home Depot. They are rubber bumpers or something.