How expensive is it to get a chuck reground?

The 3 jaw chuck (about 8") in our manual lathe is getting pretty bad, several thou out of round and several thou of taper which makes holding small or long stuff about impossible. How expensive would it be to have someone come in with a toolpost grinder and clean up the jaws? We're in Maryland, between Baltimore and Washington, DC - recommendations welcome. Thanks.

-- Regards, Carl Ijames carl.ijames at verizon.net

Reply to
Carl Ijames
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More expensive than buying a new chuck

John

Reply to
John

A couple of things can lead to poor centering: one can be ground out and one cannot.

If your problem is JAWS that are worn, either in the grip area or in the scroll teeth behind the jaws, you might be able to improve the situation. Consider getting an electric or air die grinder and very lightly dressing the jaws. Be sure to get a die grinder that has a clean cylindrical section around the spindle so you can grip it with a split aluminum block bored to hold the die grinder at center height mounted directly on your cross slide. Clamp the jaws down on three 1" or so long blocks BETWEEN adjacent jaws, not centered inside the jaws, to preload them. Use a somewhat resilient material like hard rubber or soft plastic for the blocks to get uniform loading of the three jaws. Grind with very light feed. Worked for me on an old chuck I acquired. Didn't make it perfect at all openings, but did improve things. Clean the chuck very well after grinding because you will have gotten grit inside the chuck mechanism.

If your problem is a worn scroll behind the jaws, you are probably screwed because the centering varies with jaw opening..

awright

Reply to
Anne Irving

"Carl Ijames" wrote in news:HShtg.8066 $F8.939@trnddc02:

Just buy a new set of hard jaws. While you're at it buy a couple of sets of soft jaws for the jobs that need to be perfect. Then just drill and bore them as needed.

You may also want to invest in a spider or some rings to help with the boring.

In all likelyhood you could bore the hard jaws you have now. A good carbide shank insert bar should do the trick.

Reply to
D Murphy

Greetings Carl, Instead of sending it out you should do it in house. On the lathe. If you don't have a die grinder then buy one. It will be lots cheaper than buying a chuck or sending it out. For grinding the inside of the jaws you will need to chuck something up in the jaws to load them properly. If the chuck has removable top jaws this is easy. With the jaws closed down to the diameter that's just smaller than the through hole in the chuck determine the diameter of the jaw bolt holes nearest to the chuck ID. Then drill and tap a ring such that the tapped holes are on the same diameter. The thread size should be as close in size as possible to the hole size in the jaw. Screw short screws into this ring leaving only a little of the screw protruding. This is because they won't be able to go very far into the chuck jaw before they hit the jaw screw head. If the head is too close to the jaw surface then face the heads down on some screws to be used just for this job. Now, with the screws in the ring located in the jaw screw holes tighten the chuck onto them. This will spring the jaws out the same way they would be when chucking on a part. Mount the die grinder to the tool post. Most likely the die grinder will need to be at an angle because the grinding wheel will probably be smaller in diameter than the die grinder body. And you want the grinding wheel as close to the grinder body as possible. If you can, use a diamond to dress the grinding wheel. One way that works is to use a C clamp to clamp a diamond dresser to a chuck jaw. Then just pass the grinding wheel across the diamond. Finally, run the lathe in the forward direction and LIGHTLY touch the grinding wheel to the inside of the jaws. Most likely the point of first contact will be at the back of the jaws. Taking small amounts with each pass of the wheel is best. Like .001". Or less. Since I don't know what wheel you will be using, how hard the jaws are, how fast the die grinder spins, and lots of other variables I can't tell you how much to take off with each pass, how fast to spin the chuck, and what feed rate to use. You will just have to find out what works best in your situation. You will need to dress the grinding wheel more than once. Check the wheel for glazing. This means the wheel is getting dull. It will actually look kinda shiny. When the jaws are ground to your satisfaction make passes to spark out. So you will be making spring passes until the wheel no longer makes any sparks. And make sure when doing these final passes that the wheel isn't glazed. If you turn off the die grinder you should dress the wheel when you turn it on again. MAKE SURE EVERYTHING IS COVERED WHEN GRINDING THE JAWS AND WHEN DRESSING THE WHEEL. I CAN'T STRESS THIS TOO STRONGLY. You don't want any abrasive dust getting into the moving parts of your lathe and destroying the accuracy. After the grinding is done take apart the chuck and clean it. Actually, you should take the chuck apart BEFORE grinding and clean it. Then of course clean it after grinding. And clean the lathe too while you're at it. Make sure you can put the chuck back together the same so that it's still accurate after grinding. It's best to have the lathe free of oily surfaces when grinding to keep any wayward dust from sticking. ERS

Reply to
Eric R Snow

Thanks for the advice, all. I guess I wasn't completely clear - we don't want to send the chuck anywhere and we didn't really want to try to mount or adapt a die grinder, we were hoping to find someone with a toolpost grinder who could come to our shop and do it on our lathe. The scrolls seem in good shape and we are going to buy new hard jaws, but the jaws in the chuck that the hard jaws bolt to have a lot of taper. No one here has done this job before so we were hoping to just get it done :-).

-- Regards, Carl Ijames carl.ijames at verizon.net

Reply to
Carl Ijames

It seems that you are either unclear about your objective or would rather not say. You define approaches you don't what to take without saying why you don't want to take them. Do you just want a chuck that runs true for least cost, or is it important to you to restore the chuck you have? I don't care either way, but I think you need to answer that for yourself.

Chucks are mass-produced, repairs are one-off skilled labor. Good 8" chucks aren't all that costly. If you merely want a chuck that runs true, it would surely cost less to buy a new one or good used one than to have someone come to your shop to restore your old chuck.

Reply to
Don Foreman

I don't understand why you don't want to adapt a die grinder. Is this because nobody there has the skill? By the time the chuck is ground somebody will. If you pay to have the chuck ground it will probably cost as much as a new chuck. I have a nice Dumore tool post grinder. If I went to your shop I would charge you for not only my time there but my travel time from my shop to yours and back. And so would anybody else. Maybe you can find a hobbiest who is willing to do this for cheap or nothing. No guarantees with that approach though. ERS

Reply to
Eric R Snow

For something like that, figure 100 dollars per hour. Door-to-door.

You can buy a lot of chucks for that, eh?

Jim

Reply to
jim rozen

============== See

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take a good look and make one up your self from scraps if you have welding capability. Will fit almost all air die grinders and drimel style tools. If you have shop air see
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?Itemnumber=47869if no shop air see
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No dumore, but the price is right, and for a one-time job.....

I made one up and it works like a champ in the standard square of QC tool holder. Be sure to cover the ways/bed of the lathe. I use plastic trash bags and racer tape, with saran wrap on some items.

Time to add to your repertoire of "shop skills." I covered this in my second semester "crafts machining classes."

Unka George (George McDuffee)

There is something to be said for government by a great aristocracy which has furnished leaders to the nation in peace and war for generations; even a democrat like myself must admit this. But there is absolutely nothing to be said for government by a plutocracy, for government by men very powerful in certain lines and gifted with the "money touch," but with ideals which in their essence are merely those of so many glorified pawnbrokers.

Theodore Roosevelt (1858-1919), U.S. Republican (later Progressive) politician, president. Letter, 15 Nov. 1913.

Reply to
F. George McDuffee

According to D Murphy :

This is assuming that he has a chuck with two-piece jaws. If not, the game changes to restoring the existing jaws. And if it is that badly worn in the jaws, it may also be equally worn in the scroll plate and the threads on the back of the jaws, so while he might be able to improve the grip, and to get it to grip true at a single size, other sizes can still be way out of size.

Perhaps -- though carbide is not too pleased with interrupted cuts, and this would be the grand-daddy of all interrupted cuts.

I would consider a toolpost grinder -- either a real one, or an improvised one (such as an air driven die grinder mounted to the toolpost, to be the better route with re-facing the jaws. But *any* grinding on the lathe requires a lot of protection of the ways (and many other parts, followed by a lot of careful cleanup after you are done, to keep from embedding abrasive in the carriage to wear the bed every time you move the carriage.

Good Luck, DoN.

Reply to
DoN. Nichols

According to Carl Ijames :

Huh? Are you trying to grip workpieces with the master jaws (the part which lives inside the chuck body)? You should not be doing this. The gripping should *always* be with the top jaws -- either hardened ones, or soft jaws custom bored to fit the workpiece.

I'm not sure that the inner ends of the master jaws are even

*expected* to form a true surface -- though it is convenient to grip on that while grinding the top-jaws true.

If you are complaining about taper even with new top jaws, then the wear in the master jaws is not on the surface which would be improved by toolpost grinding. It is wear in the slots which fit the jaws to the chuck body's ways. And *those* will not be improved by re-grinding the master jaws. The master jaws will simply be too loose (with wear both on the master jaws and on the ways in the chuck body), and the best bet there is to replace the chuck with a new one. The Bison ones are typically a good chuck for not too much money. I have bought them, and am quite pleased with them.

From what you describe, the job which you appear to be trying to have done should not *be* done. Fit new top jaws and see how they do. If *they* don't fix it, go for a replacement chuck.

Good Luck, DoN.

Reply to
DoN. Nichols

snipped-for-privacy@d-and-d.com (DoN. Nichols) wrote in news: snipped-for-privacy@news4.newsguy.com:

I don't know that I've ever seen an 8" 3-jaw that didn't have replaceable top jaws, but I suppose they exist. But even one-piece jaws can be replaced. As can the scroll, etc.. But it gets to a point where you may as well buy a new chuck. If run out is critical get an adjustable one like a Buck Adjust-Tru.

It's funny too how people won't hesitate for a second to use soft jaws in a CNC lathe, but not on an engine lathe. It's hard to beat soft jaws, bored in place, for run out. If that's what you're after.

Reply to
D Murphy

According to D Murphy :

It depends on just how old the machine is. I believe that at one time, *all* chucks used one-piece jaws.

*If* the maker is still in business. The fit of jaws to the chuck body tends to have quite a few critical parts, including the teeth to match the particular scroll which you have.

Given enough incentive, you could make *all* the pieces for a chuck -- and if it is sufficiently worn, that might be the only way to get it true again. :-)

Amen. Even the Bison line has their own implementation of that feature -- and one well worth having, in my mind.

*I* use soft jaws. You'll find other regulars here use them. I made sure to buy a couple of sets when I bought my 6-1/4" Bison -- and I paid extra to get the version of the chuck with the two-piece jaws. I've even used soft jaws on the old Unimat SL-1000, and they are the *only* kind of jaws for the 3-jaw for the Taig -- which has caused me to use it for certain tasks which needed repeatability -- including repeatable depth.

Enjoy, DoN.

Reply to
DoN. Nichols

First, I'm sorry if it seems I'm slow replying. I post from home and have been fighting disk problems so connect time has been spotty. We have no sentimental attachment to this particular chuck :-), we just want to hold better tolerances. Since no one over in the shop has experience doing this or having it done, we didn't know which would be cheaper: a new chuck, paying for someone with the right tools to fix our chuck, or investing the time for our machinist to teach himself how to do this. [I sometime make some chips on the manual lathe and Bridgeport for fun but I'm no machinist, I'm an analytical chemist with a background in ultrahigh vacuum systems, supercon magnets, and mass spectometers.] I think the above quote is the most concise and best advice for me to pass on to our machinist. We do use soft jaws when needed but the hard jaws definitely need replacing. After that we will see how good the chuck is, and see if we need to just get a new one. Thanks again everyone for the advice.

-- Regards, Carl Ijames carl.ijames at verizon.net

Reply to
Carl Ijames

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