RD's Blog

The Hobbyist Machine Store

1513sThe Taig 4 Jaw 3 1/4" dia. self centering scroll chuck (#1060) Is a handy, fast centering 4 jaw chuck. All four jaws move together just like the three jaw chuck. But that is a bit of a problem. A self centering chuck is for center holding. Three jaw chucks do this well as they perform much like a three legged stool. (The kind of stool you sit on to milk a cow) Ha!

The three legs (Like a camera tripod) always set stable on uneven surfaces. Add a forth leg, or in the case of the milling chuck, a forth jaw, the legs must be perfect in length or the table (or part held in the jaws) wobbles. We have all experienced this a some point with a table or four legged chair.

In machine shop work, even the smallest of deviation in length can easily be seen but not tolerated. The Taig self centering aluminum chuck jaws are mass produced and all jaws are not absolutely all the same. There is always manufacturing variance.

Taig could add an extra manufacturing truing step in producing the chuck. But it adds to production cost. And at some point the machinist/user may want to change out the jaws. They are replaceable. The truing is a very simple process that every machinist needs to learn and perform. The jaws are aluminum and therefore quite easy to machine.

The only tool necessary is the Taig boring bar tool bit. It's one of tools bits in the set of six that can (and should) be purchased with a new Taig lathe.

Here is the process:

1. Clamp a round (a US Quarter will work) thin disk in the rear of the four jaw chuck firmly (without mashing the disk). Clamp it flatly in place against the back face inside the jaws. Do not atempt this process without this step!

2. Set the lathe on the slowest lathe speed.

3. Set up the boring tool directly in-line with the rotational axis. Not super critical but one needs to maintain the proper boring tool angle clearance that is built into the tool.

4. Set the lathe depth stop so the boring bar doesn't hit the disk in the back of the chuck.

5. Carefully hand test the rotation so the tool just clears all four jaws.

6. Start the lathe (set on slowest speed).

7. Move the cross-feed out until you just hear the tool "ticking" the inside edge of the jaws at the very front of the chuck

8. Slowly and evenly feed the tool towards the preset stop to the back of the chuck.

9. Repeat slightly backing the cross-feed on each run (and checking) until all four jaws are being faced the full depth. This isn't very much material so take very shallow cuts. This is interrupted impact milling, not continuous cutting, but the aluminum and shallow cuts do no damage to the tool.

10. When all four jaws have been machined you will have a very true running bore within the chuck.

11. Remove the disk (Quarter) and use a small file to remove the very slight lip at the rear that was holding the disk.

You now have a very precise #1060 Taig self centering 4 jaw chuck. Total time certainly less than 15 minutes. If you loosen the jaw mounting screws, replace the jaws, or make any other adjustments, to the chuck (disassembly for cleaning) you MAY have to perform this truing again. Now you know how!


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