Video - modify jaws to increase 3 jaw accuracy

I did a little experiment and took a video of it. Worked out pretty well for me. If you know other techniques to add, let me know.

https://m.youtube.com/watch?v=87FamWJ6HTc

Whiners and complainers, feel free to ignore this. Or, better yet, post your own video that is more helpful

buy a chuck with two piece jaws.

Could have just ground the old jaws round and been done. The main thing to remember is we're talking about a scroll chuck. You're not going to get great repeatability especially at different diameters. If you want a scroll chuck that can be set accurately for runout, buy one that has a "Set-Tru" feature. Better yet, just use the 4-jaw. It really doesn't take that much time to set one, and it's infinitely adjustable.

iwananew10K said:

buy a chuck with two piece jaws.

Click to expand...

Learn how to use a 4 jaw....

eKretz said:

It really doesn't take that much time to set one, and it's infinitely adjustable.

Click to expand...

One trick I use is to pre-set the jaws with a scale when making large diameter changes. You know the stock/part's radius, you know the chuck's radius, and you know the jaw's length. Do the math and you're pretty close, pretty quick. It also work well for offsets.

Where do I begin? Oh, never mind; it's just too much. A total waste of time.

We would be better off allowing serious discussion of the banned home shop machines than to allow this kind of method being seriously discussed.

wait...someone is discussing it seriously??

i actually thought we were being trolled.

Pretty ballsy post. Must like to be abused.

Well, a guy can waste his time as he sees fit, no issue with that

In the initial condition, one could maybe have corrected the runout with a judicious tap with a soft hammer. The actual runout error is only half what you see on the indicator, because it is doubled by rotation to opposite side of the spindle axis.

Personally, I like jaws that are harder than hell on a general purpose one piece jaw. Soft materials will mush out in short order and will require constant reworking. As a matter of fact, I had the jaws on my 12" Rohm combination chuck hard surfaced with some sort of hard surfacing rod. It was a tad bumpy to knock the lumps off Anyways, they have stayed nice and straight for a number of years, despite the odd slippage incident or two.

For those that say it was a waste of time, results don’t lie. It improved the tir, so go back to complaining about something else.

Epa, congrats on making my ignore list. #5! Not sure what you have to gain badmouthing my experiment considering the results. Do your own video since you are smarter than everyone else. If you’re going to act like a jackass, at least grace us with a bit of your omniscience

Cole2534 said:

One trick I use is to pre-set the jaws with a scale when making large diameter changes. You know the stock/part's radius, you know the chuck's radius, and you know the jaw's length. Do the math and you're pretty close, pretty quick. It also work well for offsets.

Click to expand...

Cole,
I definitely need to suck it up and use the 4 jaw more. When chucking barrels, it doesn’t bother me at all and doesn’t take long. Just being lazy. Good technique

eKretz said:

Could have just ground the old jaws round and been done. The main thing to remember is we're talking about a scroll chuck. You're not going to get great repeatability especially at different diameters. If you want a scroll chuck that can be set accurately for runout, buy one that has a "Set-Tru" feature. Better yet, just use the 4-jaw. It really doesn't take that much time to set one, and it's infinitely adjustable.

Click to expand...

Already ground the old ones once. Turned out fine, but wanted to try this. Set tru is definitely on the list

The last time I priced hard jaws for my chuck it was over $400 and 2 months away. I guess if you're running Chinese crap it's no big deal to take an angle grinder and buzz box to your "hard" jaws. I can make (or buy) a hell of a lot of soft jaws for the price of one set of hard jaws.

My comment may not be welcome, so sorry if it isn't. Or I may already be on the Ignore list.

In the before scenario you had .0015" TIR (not runout) next to the Chuck, and .007 TIR away.

In the second scenario you had .0015" TIR next to the Chuck, and .002" away.

So, for the sake of argument or exercise, what is away from the Chuck upon Chucking is irrelevant. The TIR next to the Chuck is the only thing that matters. Like someone else pointed out a little blink on the bar with something, probably would have brought that .007" in. But in the process you have essentially changed your hard jaws into soft jaws. Not criticizing, other than to say you can do about 10x better. If I bored jaws and there was .0015" TIR, that would be unacceptable. And if I turned hard jaws into soft ones that would be BAD.

I'm not making a video just to prove it.

R

sent you a PM...hope it helps.

Mram10 said:

For those that say it was a waste of time, results don’t lie. It improved the tir, so go back to complaining about something else.

Click to expand...

Mmmm, supposedly this is a forum for professional people. It's nice that you are having fun but no machinist in his right mind would spend even five minutes doing what you did.

Then if he made a video of it, we'd laugh him off the planet.

FWIW, I would not use this procedure, ever. Here's why:

First, as others have pointed out, the reading you got away from the chuck is of little value - there can be enough movement in the way the jaws fit into the chuck and the way the part fits into the jaws to allow some movement out at the end of the part. Consider how much deflection you would get if you were actually trying to turn the part way out there without support from a center! I would guess if you removed and re-chucked the part 5 times, you'd get 5 different readings out at the end.

Second, welding produces stresses in whatever is welded. You might be fortunate enough not to induce enough distortion to mess up the fit of your jaws in the chuck ... or not. In any case, precision fits and welding do not go together in my book. (Yes, you machined the jaws afterwards ... but I'm talking about the sliding surfaces where the jaws fit into the chuck.)

Third, and related to the above, unless your jaws are mild steel, welding the soft jaws onto the original jaws runs the risk of cracking due to the stresses induced by welding. If the jaws are cast iron, you would be very lucky not to crack the jaws; if they are a hard steel, you are risking cracking at the joint. If they are mild steel, you can weld with no concern for cracking (though still concern for distortion) ... but if they are mild steel, then you might as well just bore the jaws without bothering to weld something else on.

Glad it worked out for you, but I would suspect that no professional machinist on this forum would dream of following this procedure. I certainly wouldn't, even as a hobby machinist - I value my tools too much to take this sort of risk, especially when it is totally unnecessary; 4 jaw or replaceable soft jaws for me ...

I’ve been to 3 world fairs and a pig fuck and I ain’t never seen nothing like that.

How advisable is it to stick weld mild steel to hardened iron jaws?, I suspect one small crash is going to break off the mild steel and allow whatever's being turned to be flung out of the jaws at speed.

Grinding your hard jaws in the chuck while preloaded is the accepted method of trueing up the jaws: