After spending then past week doing automotive work on the Jeep and for a friend, I had a bit of time to try to resolve a problem that cropped up a while back.
I have been using a nice keyless chuck on my mill, and had it mounted on a PhaseII R8 arbor. After using it for 6 months or so, it stopped being about to be secured on the mill. While it would work fine on a mill with a manual drawbar, my air-operated drawbar would not engage. It seems that the top thread in the arbor had gotten stripped, and my mill's drawbar is too short to reach further down.
My solution was to try to make a straight-shank arbor with a JT33 taper on one end to match the chuck.
Since the large end of a JT33 taper is 5/8" diameter, the only thing I would need to do is take some 5/8" round bar and turn the taper on one end. The length of the taper itself is 1", and from Machinery's Handbook I was able to determine that the taper angle is ~1.8 degrees. I chucked the PhaseII arbor in the lathe suppored by a live center to ensure that it was mounted straight. Setting the compound to 1.8 degrees, an eyeball check showed that the sides of the compound were very close to parallel with the taper on the arbor.
To get the taper as exact as possible, I removed the QCTP and mounted a dial indicator to the compound via a magnetic holder. Once I had it adjusted so that the tip of the indicator was at center height with the taper, I advanced the compound slide to read the variation, almost exactly like tramming a milling vise via the fixed jaw. My first pass was only about .002" off over the 1" of the taper, and with a few adjustments tapping the compound, I had no visible deviation over the length.
Cutting the taper thereafter was just a matter of moving in the cross slide .01" each pass and then slowly advancing the compound. The total infeed for this taper is about .062", so I made 6 cutting passes, followed by a final finish pass as slow as possible. A bit of polishing with Scotchbrite and I was ready to test the fit.
I got a very tight fit the first time I inserted the taper into the chuck, and in fact I then couldn't remove it with hand pressure, so it should work well going forward.
FWIW, I removed the chuck from the old arbor using a "pickle fork" tool. I also used the steel rod recycled from an old Jeep shock absorber. I have no ideal what steel it is, but it is very smooth and round and machines very easily.
