Debur Internal Taper On A Jacobs Drill Chuck?

I recently picked up a drill press with a Jacobs chuck which mounts on a 33JT spindle taper. The chuck is in excellent condition other than that is has a raised score / galling about midway into the taper. I was able to dress the taper on the drill press spindle with a stone. Wondering how to go about dressing or recutting the taper socket in the chuck.

I've got a SB H10 lathe and a good 4 jaw chuck. Thinking that I'll need to press the locking collar off, strip the chuck down and rework the taper socket on the lathe, but how?

Lots of options have crossed my mind:

Find a 33JT reamer.
Use the spindle to adjust my taper attachment and re-turn the socket (not likely, as they would be reversed).
Turn and arbor to match spindle taper, and then use it and some grinding compound to dress the chuck.

Or should I just cough up the money and buy a new chuck? (kind of defeats the purpose of having a lathe..)

Any suggestions would be welcome.

Thanks,
John

Hi John,
as a suggestion,
turn a matching JT33 taper in copper or brass and use a light slurry or coating of abrasive dust, you could in effect create a lap and remove the highspots.
the abrasive will embed into the soft copper/brass and may make a very nice alternative to a reamer albeit a little slower to clean up very damaged sections.

Thanks Doc, I'll give that a try.

About securing the chuck in the lathe. I could strip it down and secure the OD of the chuck body in the 4 jaw, or leave it intact and tighten it down on a 1/2" ground rod secured in a collet...... Hmmmmm..... There is virtually no wear on the bearing surfaces of the drill chuck jaws. I don't know how true the OD of the chuck runs in relation to the jaws...... Any thoughts? I'm leaning towards clamping the chuck on a ground rod mounted in a a collet...

I would check a chart for the taper dimensions, like this one:
http://victornet.com/reference/Morse_Jacobs.html
and then use two indicators to set the compound slide angle to the correct change in radius over the correct longitudinal distance (not the taper length travel using the compound dial.) Note that you will be measuring the change in radius and the taper spec is given in diameter. Chuck the nose of the drill chuck in the 4 jaw, where the key holes are, and dial it in on the rear of the chuck body, not the rotating shell. Strip the chuck if necessary. It is important to have both ends of the drill chuck body somehow simultaneously dialed in to minimize runout. Then use a sharp boring bar set on exact center height to cut the taper to the minimum possible extent to remove only the high spots, stop just below the original taper surface. Do not try to clean up the entire taper or the male taper might bottom out in the chuck before the tapers engage each other.

Edit: Note that you can also mount the arbor between centers and re-cut it as well if necessary, using the same method for setting the compound slide.

Thank you Bob. Very helpful guidance.

If it is just one small area that has the defect you might take a diamond coated rod and just take down the part of the defect that is raised. If you leave the rest of the taper untouched it will hold the arbor tightly and accurately and I doubt you would notice the defect is even there. Once you touch the taper you will throw it off unless you get it absolutely dead on.

Personally, I would go for a diamond rod myself. EZLap makes a nice one used for sharpening fishing hooks that works well for this job. It has a tapered tip that lets you file just a small area. I've done 3 Albrecht chucks with this very problem and got all of them to work just fine.

mikey said:

If it is just one small area that has the defect you might take a diamond coated rod and just take down the part of the defect that is raised. If you leave the rest of the taper untouched it will hold the arbor tightly and accurately and I doubt you would notice the defect is even there. Once you touch the taper you will throw it off unless you get it absolutely dead on.

Personally, I would go for a diamond rod myself. EZLap makes a nice one used for sharpening fishing hooks that works well for this job. It has a tapered tip that lets you file just a small area. I've done 3 Albrecht chucks with this very problem and got all of them to work just fine.

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That is a better idea than mine, Mikey, if the damage is relatively minor and confined to a small percentage of the tapered surface.

Bob Korves said:

That is a better idea than mine, Mikey, if the damage is relatively minor and confined to a small percentage of the tapered surface.

Click to expand...

Totally agree, Bob. If the damage is minor then getting rid of the defect will not alter the interference fit. If it works in my klutzy hands then I'm sure it will work for others.

This is the tool I was referring to: https://www.amazon.com/EZE-LAP-Sharpener-Unique-Shape-Groove/dp/B0001WP21Y

If the damage is narrow, as suggested, only remove the damaged area. But I would cut a groove rather than mess around with a hone or stone of some sort. This won't change the remaining taper, and eliminate the need to dial the ID in dead on, so you can hold it any way you want. Either on a pin (larger the better) or simply chuck the nose. Use your pinky and some abrasive paper/cloth to make sure the groove doesn't leave any burrs, etc.

Actually, thinking about it, with the drill chuck nose mounted in a lathe chuck, a Dremel with a small stone could be used to work on a fairly precise area, turning it around to get the full diameter.