Trueing a lathe chuck

DelMN

Member
I have a 5 inch 3 jaw chuck (Atlas 618) that is worn near the ends of the jaws and it is impossible to get the wobble out when I chuck anything. I was thinking about taking it to a machine shop and let them true it. I don"t have the grinder, etc, to do it myself. What do you think it would cost to have a shop do this? Any other ideas?

Thanks for your replies.
 
I think you could buy a new chuck for what it would cost to grind your chuck.
I have done this myself with mixed results and have never used a three jaw chuck, even new, that would hold closer then one and one half to two thousands consistently. Wear in the screws and gear contribute to inaccuracy also.
Much better to use an independent chuck (four jaw) that you can adjust to .000
 
New China made chucks are pretty good, but given the age of the lathe a new chuck still isn"t going to turn it into a new lathe....but I think you know that already. That said, if your not worried about holding a tolerance in the tenths, you can easily do it yourself with nothing more than a straight shaft grinder. I used a pneumatic one, but pneumatic or electric either one should work just fine. I say do it yourself because then it will be ground true with YOUR lathe, not ground true to someone else"s lathe, and that"s what"s important to really maintain a decent tolerance.

What Dad and I have both done to get worn three jaw chucks to maintain a decent tolerance on our lathes is to make a mount for your tool post that will hold the grinder and allow you to move it just like you would a tool bit. Since both machines had a quick change tool post we used a piece of sqare stock so it could be held in one of the tool holders, and then a suitably sized piece of angle iron to hole the grinder. The grinder is nested in the angle, and held tight with several hose clamps.

Once everything is together and rigid, chuck up a piece of heavy wall tube large enough to keep the chuck open, on the outside of the jaws. That is assuming you have stepped jaws that allow you to do that, otherwise grinding isn"t going to work. With the jaws tight against the tube, and therefore round you can then use the grinder to true the inside. What I so is start the lathe with the chuck turning relatively slow, and with the grinder running continuously. Then put the stone inside the chuck and back it out until it just begins to touch the jaws. From there back it out of the chuck, feed the stone into the chuck a thousandth or so, and start the feed. In other words use the grinder just like you"d do a tool bit if you were machining an ID with a boring bar.

Like I said, both myself and my Dad have both done it to several chucks and had pretty good results. It won"t make up for a chuck that is completely worn out, or turn an old lather into a new one, anymore than putting a new chuck on it would, but it can get a chuck with worn jaws to turn relatively true again.
 
A new 5 inch chuck from littlemachineshop.com run's about a hundred to one twenty. They are pretty decent chuck's.

You can true up the one you have with a grinder or a toolbit but it takes patience. Open the chuck to the same diameter as the through hole and run it at full speed so the jaws will all stay out like they're supposed to. It would be best to make sure the chuck is thoroughly clean before you start. Do a Google search and you'll find a lot of good info on it.
 
you may google the chuck and buy new jaws for it i have rebuilt a many of them and generally speaking the new ones come to you over sized a few hundred thousands over for the play if need get you a lapping stone and take some mineral oil just keep the stone good and flat to the jaw and swipe it a couple of times or untill it fits you can any parts for it to rebuild it yourself it is really easy and like every one else says compar price unless you want that one chuck
 
I used the same process that NC Wayne described. Used my air grinder with hose clamps on a tool holder. Hard part was preloading the jaws. There are videos on Utube doing this. I got mine down from .006 down to less than .002 but I had to grind it about three times.
 
I need to true mine up.

I am planning to use a grinder and use large washer with a cut in it for pre-loading.
 
Are you sure it's just the jaws that are worn out? The scroll plate that drives them also wears out... You can try the method Wayne has suggested, but if the scroll is bad then the chuck will run true at one diameter only, where you grind it. Like I said before, get a 4 jaw ))
 
Look up a Buck "set-tru" 3-jaw chuck. They use a regular 3-jaw scroll, but there is approx 0.06" clearance between the chuck and adapter plate diameters. The face bolts hold the chuck to the adapter plate, and 2 sets of opposed set screws (sometimes 8) around the chuck OD are used to stir in the workpiece. Runouts of 0.0005" or less are obtainable in seconds.

They aren't cheap, but you can make your own quite easily with a plain back chuck and an adapter plate that fits your machine.. Once you use one you'll wonder how you ever lived without it.
 

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