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Chuck jaw grindig

9100

Diamond
Joined
Nov 1, 2004
Location
Webster Groves, MO
I seem to recall a post about a ring to tension the jaws on a three jaw chuck for grinding. You want to tension the jaws like they were holding a part and I think it had projections that fit between the jaws. A search is pointless because the words are used so often.

Bill
 
You talking about the rings used to hold soft jaw under tension so they can be bored? See usshoptools (and I'm sure others.)

If you are trying to grind out taper, seems to me you want to load up the jaws so they'll deflect in the expected direction - but the plugs used are just turned on a lathe - not super special.
 
Bill,

You are looking for a Jaw Boring Ring. There are a few styles, but they do the same thing. I recently posted pics using mine in the turning center. Recently meaning within the last two months... Good luck.
 
Rings are not all the same.

Holding jaws deep in the chuck is quite dissimilar to loading the jaws at the tips.

Best for me has been to lap the jaws with a brass bar (1 inch plus)
Just lightly close the chuck jaws down on the charged bar (sacrificial) The lapping bar must be located by means of an accurate tail stock center.
Hand pressure is sufficient to hold the bar from rotating with the chuck jaws.

Figure out a way to "stroke" the lap, and you really have something!
 
When I grind hard chuck jaws, I do them on the surface grinder with the appropriate radius dressed on the wheel. That way I can grind a slight taper to the jaws so in use they grip at the front first. It depends on the amount of wear in the chuck body, but about .0002" taper is where I start. Next is to reinstall them in the chuck and indicate a ground bar. Then regrind the offending jaw until the bar runs true.

I little tedious, but I have had good success.

Bill
 
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The idea is to load them at the tips. It is a two piece jaw one that I ordered as a plain back and converted it to an adjust tru. I made a D1-6 backing plate that extends into the chuck body and the body has 4 1/2-40 tapped holes around the periphery. I can adjust for good concentricity at the jaws but it is disappointing about swash. I can get round stock centered at the jaws and it will be several thousandths out a few inches from the them. I just did a batch of parts that had the OD turned and flipped around to finish the other end. I noticed that if the jaws were cracked open barely enough to slide a part in, it would only go in to the bottom of the removable jaws. The inner jaws have a couple of teeth that should line up with the reversible ones, but are a few thousandths higher.

All right, it is a Chinese chuck. I will accept my forty lashes and move on.

In the past I have put slugs between the jaw tips, but I was looking for a device specifically made for the operation. Wear is negligible so I probably really don't need them, but I want to get it right. Grinding the two parts as a unit on a surface grinder is an option, especially since I can adjust concentricity instead of having to have the jaws perfectly matched.

I wonder how I managed to say "grindig"? My N key works.

Bill
 
99% of the time it is a waste of time to grind the jaws. the scroll is never worn evenly. you start off with a chuck that is a bit off at all diameters and up with a chuck that is right on at the diameter you ground it at and miles out at other diameters.
 
I completely understand the concerns of people that advise alternate methods and the reasoning makes sense when considering it. I am left to wonder if it is a case of "beating the monkey"**, however...

Frankly, my experiences have contradicted the admonitions. To be clear, I am not saying that the alternate methods do not work. We know that they do. What I am saying is that after careful measurements and uses, my results do not agree with the cautions against the method. I repeatably achieve .0002" - .0003" runout up to 12" away from the chuck, and all the way back to it after grinding the jaws. Flipping parts that have been previously turned yields good results, as well. ( I actually have to do that fairly often )

Of course, I am not advocating that one not use their head. Quite the contrary. I took the time to choose the size of the radii that were ground as well as precautions against grinding dust infiltration. And, of course turned the chuck pressure down to suit the application. ( in Bill's case, it would be manually )

After having done this a few times now, I find the results very predictable and very repeatable. Also, easier and faster than other methods. So when I hear or read things like this, I have to wonder if someone has been beating the monkeys.

One of my posts is here - http://www.practicalmachinist.com/v...red-soft-jaws-337081-post3001958/#post3001958

** - The old story goes that there is a cage of 4 monkeys. The keeper throws a banana into the middle. When a monkey reaches for it, all the monkeys are given an electric shock as a warning not to touch the banana. This continues for a while, until one day all the monkeys will not reach for a banana thrown into the cage. Later, one of the monkeys is swapped out for a new one and a banana thrown in. The monkey starts to reach for it, but the other monkeys beat them and prevent them from doing so. The process is continued until eventually all of the monkeys are replaced.

At this point, we are left with a cage full of monkeys that will not touch the banana.

... but no one really knows why... They just know that they can't.

So we're left with Henry Ford's admonition. "Whether you think you can or you cannot; You're right."
 
I should add that the other reason that I use the method I do is so I can grind a large enough radius on the master jaw. If you grind the jaws in the chuck, then you are limited by the through-hole size. I guess the same holds true for one-piece jaws.

The last set of jaws that I ground was for a 10" chuck. I think I ground a radius that was about equal to the maximum diameter that the chuck could hold.

I think it was whatever radius was on from the manufacturer.

Bill
 
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Life is like an onion. You peel off a layer and just uncover another, meanwhile crying from the fumes. The fixture Morse referenced is what I was looking for, but I can't move the jaws out to near the maximum diameter because the part I have to grind is buried below the chuck face. It looks like the best I can do is to grind the jaws set just inside the center hols in the chuck body, using the fixture to load them, then indicate them in a vise on the surface grinder and grind a larger radius parallel. The scroll variation doesn't bother me because it is now an adjust-tru chuck so I can center it at different diameters.

Bill
 
I can say that I made a fixture for my Foredom tool to attach to the toolpost of my lathe. And I was able to grind the OD jaws of an old 5" Cushman chuck and make it grab more repeatedly and closer to on-axis of the bed, than it was before. And all I did was make a ring for the outside of the OD jaws - I went the easy way. You could look at the jaws and see they were tapered prior to grinding. My fixture got the jaw faces mostly back to straight when viewed under a magnifier.

It certainly didn't make it brand new and repeatable, but I would estimate it improved the chuck by at least a factor of two, in my mind. Made a lousy chuck actually usable, but didn't make it a cream-puff.
 








 
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