Out of true chuck part 2

Found something that works. Y'all tell me if I am screwing up. I have found that if I hit the jaws with a plastic faced hammer while I am tightening my chuck I can get every bit of the runout out. Thinking back, I've seen my friend and full time machinist do the same thing on both three jaw and four jaw chucks. Is this a standard practice or am I damaging my chuck?

Chuck is a new Chinese that came on my new Precision Matthews 13X40. Spindle face runs true as does the chuck body itself as long as the chuck is mounted in the same position every time. D1-4 mount. Never had these problems on my old Sheldon 11 X42 but it was a well worn machine of 1942 vintage

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I'm guessing you must be talking about a lathe. I know a long time ago a guy who worked for me showed that no matter how hard you muscle the key in a hammer drill the chuck will vibrate loose when you are hammering a hole in concrete or hard brick, but if you go around the chuck tightening as hard as you can at all three holes it takes out the play in the mechanism and it holds a lot better. Can't say if you are damaging a chuck this way or not, but I know it worked, and the chucks on our drills usually outlasted the motors as hard as we used them. (Now I have a couple Spline-Drive and SDS rotary hammers for this type work.)

Bob La Londe

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Bob La Londe

Greetings Gerry, Consider just the chuck itself and not how it mounts to the spindle. Inside is a scroll plate which is centrally located by its bore. This bore must be a close fit on the register in the chuck body itself in order for the chuck to repeat. The jaws are located by the scroll. This means that the scroll, which is a spiral, must be machined accurately and on center with the bore in the scroll plate in order for the chuck as a whole to repeat. If the jaws and their associated scroll sectors are machined accurately then they should repeatedly chuck parts on center. When the chuck is tightened the scroll plate is subjected to offcenter loading which will tend to push it against the side of the bore in the scroll plate. If the bore isn't a close fit the scroll will shift off center. So hammering on the jaws may be shifting the scroll back to center. It's also possible that there is dirt in the scroll and chuck body that is shifting around. Your best bet is to take apart the thing, clean all parts well, and measure the clearances. Then you can determine what is really going on. Think about this: it's possible that if hammering on the jaws brings the part on center then cutting forces may push the part off center. Then it will be really hard to decide what exactly is happening. Eric

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No, your chuck is already damaged! The jaw slots must be loose already. My new Phase-II chuck had jaws so tight that you could not move them by hand, when new. They are still a VERY snug fit, although they have loosened up enough that you can move them across the backlash in the scroll teeth by hand, now.

You may want to at least screw the jaws all the way out of the body and clean the scroll teeth with a rag and re-oil. There may be a lot of grinding grit in there. Make sure you get the jaws back in the same slot they came out of. If these are

2-piece jaws, you should remove the top jaws and clean under them, too.


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Jon Elson

Years ago, when I was an apprentice, we were taught that no chuck ran true. If you wanted a specific part to run really true you set it up on either a face plate or a four jawed chuck and then indicated it.

In fact, once you made the first cut on a piece in a three jawed chuck you might remove the entire chuck and work but you never removed the work from the chuck.

Bruce-in-Bangkok (correct Address is bpaige125atgmaildotcom)

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Bruce in Bangkok

In my mind, beating on the jaws will greatly facilitate over tightening the chuck with resultant distortion of the scroll. Gerry :-)} London, Canada

Reply to
Gerald Miller

All the 3 jaw chucks I have, 4 in total, have a master pinion marked with a 0 next to it. Tightening with that pinion gives the truest running of the part. This is due to the tightening taking up the very small clearance between the scroll and its locating part.

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David Billington

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