I got a Jacobs 1B drill chuck (0-1/4") with my mill when I bought it, but didn't have a key that small to use it, so it sat on the shelf for years. I finally got tired of using the bigger chuck and got around to getting a key and decided to replace the sloppy arbor the previous owner made with something that fit better.
The first photo shows what was on there, a threaded stud with a straight section and an aluminum sleeve. The sleeve threaded into the stud and was supposed to register on the smooth section of the stud, but the gap was so big, I couldn't imagine it did any good. I never tested it, but probably should have to see how bad it was.
I decided to machine an arbor with the 5/16-24 threads and a 1/2" section to mount in the collet. The back side of the drill chuck has a recess at about the major diameter of the threads, so I machined a register there, the thread groove, and the 5/16-24 threads. If I was smart, I would have taken some photos while I was machining it, but didn't think of that until I was done.
The picture shows some sanding marks, but you can't really see it in person. I installed this new arbor and checked the runout using a spotting drill that I assumed was fairly round and came up with 0.0027", better than I expected! The back of the chuck was a bit rough and I probably should take a clean up cut on it, but I'm afraid I might screw something up and make the runout worse, so for now I am going to leave it. Below is the final assembly.
The first photo shows what was on there, a threaded stud with a straight section and an aluminum sleeve. The sleeve threaded into the stud and was supposed to register on the smooth section of the stud, but the gap was so big, I couldn't imagine it did any good. I never tested it, but probably should have to see how bad it was.
I decided to machine an arbor with the 5/16-24 threads and a 1/2" section to mount in the collet. The back side of the drill chuck has a recess at about the major diameter of the threads, so I machined a register there, the thread groove, and the 5/16-24 threads. If I was smart, I would have taken some photos while I was machining it, but didn't think of that until I was done.
The picture shows some sanding marks, but you can't really see it in person. I installed this new arbor and checked the runout using a spotting drill that I assumed was fairly round and came up with 0.0027", better than I expected! The back of the chuck was a bit rough and I probably should take a clean up cut on it, but I'm afraid I might screw something up and make the runout worse, so for now I am going to leave it. Below is the final assembly.
