4-jaw chuck dilemma

Put a piece inside your pipe before you clamp on it.
Reply to
Dave Lyon
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Jim,
Whyn't ping Harold Vardos? Harold is quite knowledgeable re. all things "Machining". I would bet he can recommend a way to clear up the excessive drag in your chuck without sacrificing serviceability.
Bob Swinney
Reply to
Robert Swinney
Crank the jaws in and out with fine lapping compound. Then wash everything real good even if you have to tear it apart.
Richard W.
Reply to
Richard W.
I use a lapping compound for this type of work called "Timesaver". This stuff won't embed and cuts the SOFTER material. Other lapping compounds, silicon carbide for example, embed into to the softer surface and cut the harder surface. One problem with lapping something like your chuck is since the fit is so tight now that the lapping compound will be pushed ahead of the piece and it's easy to bellmouth the slot. If I had the same situation as the O.P. I'd blue up the jaw and slide it into the chuck. This will show the tight spot. Then it can be filed, sanded, scraped, lapped, etc only on the interfering spots. Done this way the jaws can be made to slide easily with virtually no slop. Cheers, Eric
Reply to
Eric R Snow
I have a 6" 4-jaw chuck for my lathe. Never been
crashed, dropped or rusted. The jaws take a lot
of force to adjust. I've disassembled it and cleaned
and reassembled it with little change. The problem
is that I can't get a good feel for the forces
I'm applying when I'm centering up a relatively
thin walled part. I know not to expect to hold
very thin objects, but I can't seen to hold even
a relatively thick hollow AL part without distorting
it.
Any solutions?
Reply to
Jim Stewart
I must respectfully dis-agree with adding lapping compund and not taking the chuck all the way apart. Take it all the way apart, and figure out what is going on. Put Just the scroll into the body, and see how it fits, does it rotate smoothly? stone off any high spots. Try it with the pinion(s) and the scroll. How does it work now? Fix what needs fixing. Try the bottom jaws, without the scroll. Do they work smothly in the body? Add one jaw at a time to the scroll.
Take it all apart and clean it and lube it. Re-assemble. It will work so nice oyu will think it should be Legally required to do that to all chucks!
The thought of using lapping compoud on an assembled chuck makes me cRiNGe! Pete
Reply to
Half-Nutz
Wasn't Jim talking about a 4 jaw? I could be in error here, but I thought that 4 jaw chucks had jaws that moved independantly on individual worm screws rather than running on a scrol plate like a 3 jaw.
Reply to
Roger Shoaf
According to Roger Shoaf :
[ ... lots more snipped specific to a scroll-back chuck ... ]
He was. It is still in the "Subject: " header. Granted, there are some scroll-back 4-jaw chucks (I have one), but they are sufficiently rare, so if nothing is stated, the independent 4-jaw should be assumed.
So -- this breaks down to first trying the screws in each slot without jaws in place (some have the screws running in threads in the body, others have the screws captive and the mating threads on the back of the jaws, so you may have to run the screws the length of the threaded section of the body, or just make sure that it turns freely in place.
Then -- try the jaws -- in each slot, just in case there is a difference. Check whether the slots are numbered, and likewise the jaws. If they are not numbered, and you detect differences, it is time to number them yourself, once you find the best fits.
And the bluing compound is a good idea -- on both the guides, and the mesh of the screw to the jaws or to the chuck body. If there are tight spots in the rails, then scraping, filing or something of the sort is probably called for. (You do have safe-edge files?)
Enjoy, DoN.
Reply to
DoN. Nichols
Thanks guys, I'll try that.
Reply to
Jim Stewart
Raises hand. My mistake. I'll stand by what I said for a scroll chuck. Just a right answer in the wrong thread. Pete
Reply to
Half-Nutz
Fix
I assumed that someone smart enough to own a lathe, would know enough to clean everything out once the lapping process was done. There isn't much to a 4 jaw so once the jaws are removed you can clean around the screws with no problem with most 4 jaw chucks. I still stand by lapping the jaws in with lapping compound. Often it only takes moving the jaw back and forth 4 or 5 times to get the desired result. You most likely will take off far less material lapping than if you used a file. I shouldn't really have say to remove the chuck from the machine and do this in a solvent tank where you can flush out the grit with clean solvent. I have a 3.3 gallon solvent tank with a pump that I use kerosene in. Works great for just about everything.
Richard W.
Reply to
Richard W.
I have a 4-jaw chuck with the same problem. Upon close examination, I found that the chuck body had cracked, resulting in binding of the screw and jaw and very tight movement. The crack was not obvious until I got tired of the heavy work and looked very closely at the chuck to find out what was wrong.
Since it was a used chuck when I bought it many years ago, I do not know if I did the damage or it was damaged when I got it. I know, however, that I never used a cheater on the jaw wrench, but I did hand tighten it as hard as I could. I was surprised at how thin the metal was surrounding the screw.
awright
Reply to
Anne Irving
I have seen the same thing. One of the first shops I worked in had all steel 4 jaw chucks and most everything was turned in them. I took it that all 4 jaw chucks were that rigid and I was in for a surprise when I worked at another shop that only had cast iron 4 jaw chucks. It took longer to dial something in the cast iron 4 chucks because the chuck would distort easily. That was something the steel chucks don't do, so you can dial things in much faster. When I moved I sold all my machines and the shop I went to work in started to clean house. They threw away all kinds of chucks. I picked up several from the dumpster. The 4 jaw chuck I kept for my machine when I got one, was an almost new steel D1-6 direct mount 12" 4 jaw chuck. I haven't seen any new steel 4 jaw chucks offered for sale anywhere. I have often wondered if they still make them?
Later when I got my lathe from an auction, it came with out any chucks. That 12" steel 4 jaw chuck was my only chuck for about a year.
Richard W.
Reply to
Richard W.
After removing the backplate, the jaws stopped binding. Took small truing cuts on the back and side of the backplate, reassembled and problem was gone.
Reply to
Jim Stewart
snip--
From indications, a casting that relaxed over time, after machining. Stress has a funny way of giving us fits! (Or destroying them, as it was!)
Congratulations on a perfect repair, Jim.
Harold
Reply to
Harold and Susan Vordos

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