cleaning up a scroll type lathe chuck. .009 runout

So,
I want to clean up my soft jawed scroll chuck. it measures .009 runout out at about 3" away from the chuck. which I would assume is about .003-4 out at the chuck. (haven't got that far yet with this yet) I have identified the one jaw that's causing the issue, its high so I would need to take some material off the other two. assuming its not the scroll, which looks good, (I took it apart and cleaned everything) would I be able to take a file to the other jaws?

what I would do, is take the presumed .004 of the other two. but from what I've read, its usually the scroll. and at .009 am I wasting my time? I've got a plan to true it. but I don't want to waste my time if what I've got is okay. there was some crap inside causing much more runout, and I was able to get it down to what it is now by just cleaning it. any opinions would be greatly appreciated.

"I want to clean up my soft jawed scroll chuck."

Soft jaws are meant to be bored in place in the chuck while on the lathe so that they hold one specific diameter part, making it run very true. The jaws have to be preloaded while boring and there are several commercial and shop-made devices available to do the preload.

If you want to hold a different diameter, you do the preloading and boring again. The jaws get gradually used up as you repeat the boring operation, so soft jaws are considered consumable parts.

Larry

I'm wondering if you are referring to a chuck with two piece jaws with the standard hard top jaws or if indeed you have a two piece jaw and some soft top jaws in place. Makes a difference if you are going to try to turn 'em !!

Onepass said:

I'm wondering if you are referring to a chuck with two piece jaws with the standard hard top jaws or if indeed you have a two piece jaw and some soft top jaws in place. Makes a difference if you are going to try to turn 'em !!

Click to expand...

There is such a thing as one-piece soft jaws. Hardinge once sold Burnerd 5" 3-jaw chucks with one-piece jaws that came with the usual two sets of hard jaws. Hardinge also sold sets of soft jaws for those chucks. I have a NIB set of soft jaws for one. They have hard scroll teeth and the rest is soft.

Larry

In my opinion and experience, there are three primary causes for runout in three jaw chucks.

1. The faces of the jaws which grip the work. These faces can become worn. If this is the only problem, grinding them in place, on the chuck, may correct the problem. The problem with this is that this is seldom the sole cause of runout.

2. The fit of the jaws in the Tee slots in the chuck body. Either the jaws or the chuck body or both can be worn. There is little that can be done about this except to hope that the wear is the same for all three jaws. Fortunately, that is usually the case.

3. The scroll itself and the fingers on the bottom of the jaws that ride in it. Again, one component of the wear on the fingers on the jaws will tend to be the same on all three. This argues that they should only be replaced in complete sets of three. However, the wear on the scroll and also on the jaw fingers can be problematic when forces while cutting are not applied equally to all three jaws. An accidental blow can produce an indentation in the scroll at one jaw only. Dirt or different amounts of lubrication can produce more or less wear as the chuck is being tightened and loosened. And probably other factors. The jaws may be hardened, but the scroll may not be so it can be worn differently in different places. It would be very difficult to correct problems in the scroll itself. A new set of jaws would correct any problems with them.

It is important to check a three jaw chuck at different diameters of work size and therefore at different places along the scroll if you are going to get a good idea of what the runout and the extent of the problem actually is. Once you know that you can evaluate what, if any, corrective measures should be taken. From a practical point of view, most worn chucks are best just being replaced. I have attempted to grind the jaws on a worn chuck and it produced very little improvement as there were also problems with the scroll itself. In that case this condition was plainly obvious by several measurements taken close to the jaws but with different diameters of drill rod being used for the tests. Each diameter yielded a different runout figure and they ranged from +/-0.003" up to +/-0.012". As I said, grinding the jaw faces produced little improvement in this. That chuck has been retired and I hope to make a collet chuck from it some day when I have the time.

There are bunches of youtube videos on how to correct this.