Truing up jaws in lathe chuck

[Harold_V]

I thought of mounting it in the 4 jaw on my 14" lathe but that won't work...how can you indicate it? What would you indicate? I don't see that working.
Any ideas?
Thanks!
Russ

Sure!

Why won't it work? You have a good idea, but it must be executed properly.

Look at this as if you're building some custom tooling (which I did for years as a tool maker when I ran my shop).

Chucks, when made, are intended to be true with the body. If you chuck the smaller chuck in your 4 jaw, dial it true in both directions, restrain the jaws as we've discussed, then grind the jaws, it will be just as true as if you had mounted it by the thread. The important issue here is for you to really have it dialed true----which will take some patience. Don't let "that's close enough" get into the decision---for any error you introduce here will be with you from that day forward. It's worth spending the time to eliminate down to a couple tenths. Even closer if you have means to read that close.

Start by stoning the face and OD of the chuck body, so there's not any dings to drive your indicator nuts. The smoother the surface, the better. Set the pointer of your indicator so it trails off any openings, and don't have much "preload" on the indicator, so it doesn't bounce much. Turn the chuck by hand, always in the proper direction, so you never stub the point.

What you're doing in this instance is making certain that the jaws are concentric with the chuck body----even if they weren't originally. Makes no difference--you establish a new reference point, which is what you need for the balance of the work at hand. Remember to mark the hole (for the chuck key) you intend to use in the future, and always use that hole-----not the others. Make the mark permanent, so it can't be confused.

Once you have your chuck ground, as long as your locating pin conforms to the same setup, it will have little choice but to be true when applied to the rotab. I'd pay strict attention to the back side of the chuck, too. Make sure it's dead parallel with the front, which will have been your second reference point.

This is one case where I detest a tapered center in a rotab. I will use them only with a straight bushing. That way you are free to provide a locating pin without the worry of how long it must be in order for the chuck (or any other fixture) to seat properly. I'm not keen on the idea of a chuck being held only by the taper, particularly when you risk spinning the chuck as you would on a rotab, perhaps milling a large radius.

What I recommend is an adapter plate (aluminum works fine) for the chuck, which is held to the chuck by the backing plate bolts (the adapter plate replaces the backing plate, if that' possible), then the adapting plate has counterbored holes that match the T slots in the rotab. That way you can mount the chuck securely. That, of course, won't work if your rotab is not larger than the chuck.

Harold

[torker]

Harold...Thanks! I wasn't sure if the outside of the chuck was a sure way ti indicate the setup. That makes it easy then. I can also machine the MT with the adapter screwed into the back of the chuck....as long as the thing is square on both sides I guess.
No...I wasn't going to hold it in the R/T with just the MT plug.
I'm going to do just what you said. Machine a 1/4" steel backing plate and bolt it into the T-slots.
As you can imagine, there isn't a whole lot of room as the R/T is 6" and the chuck is 5". I'll make it work.
Do you think it would be worthwhile to buy new jaws for that ol' Buck chuck?
I realize it still would need to be ground but wouldn't this be a bit more help to tighten it up?
Thanks!
Russ

[kap pullen]

I put my jaws up on the surface grinder (individually) , clean up the low jaw first (high indicator reading on the stock), and grind the others individually to true up the chuck.

You can expect to replace the jaws in the chuck and re-indicate several times to get it done.

This was done once when the new chuck came in.

I can taper the back of the jaws a couple thou more to get full legnth gripping power this way.

On the other lathe, the locating diameter is .01 loose allowing me to indicate individual jobs true without cutting anything.

Different ways of doing things.

Kap

[Harold_V]

As you can imagine, there isn't a whole lot of room as the R/T is 6" and the chuck is 5". I'll make it work.

That's plenty, even if you have to make custom T nuts that are tapped maybe as small as 1/4"-20. It would probably be wise to use SHCS (socket head cap screws) for mounting----they're not only strong, but small in size, so they'll fit within that ½" of space you have at your disposal. Sounds like a damned good plan to me.

Do you think it would be worthwhile to buy new jaws for that ol' Buck chuck? I realize it still would need to be ground but wouldn't this be a bit more help to tighten it up?

My knee jerk reaction is no. Reason? The jaws, unlike the body, are heat treated, so the vast majority of the wear will have come at the expense of the body of the chuck. The vast majority of the error due to wear, therefore, won't be corrected by new jaws. Given the fact that they'd need to be ground anyway (I agree with your logic), the only thing you'd really gain is a lighter wallet and shiny jaws. The end result won't be any better. I'd keep those hard earned dollars for something more useful. Besides, it's possible you'd get jaws that don't fit the scroll well. I have a replacement set in my 3 jaw, of necessity because I broke the teeth off one of the original jaws when the chuck fell on the floor (don't ask ). They've worked well enough, but they don't fit the same way the originals did.

Thanks!
Russ

Better save the thanks until you get done! You might want to cuss me a little.

(Just kidding. Use good sense and this shouldn't be a hard job to accomplish, just tedious. This kind of work is lots of fun when you don't get in a hurry, and leaves you with a wondeful feeling of accomplshment, having made something useful from what is, potentially, a piece of junk.)

Be sure to let us know how it turns out!

Harold

[torker]

Harold...don't you ever sleep?
The socket head screws...my thoughts exactly. I've already made some extra long T-nuts for the slots and had planned on using 1/4" screws.
The 1/4" adapter plate'll be turned and trued from 3/8" plate.
Thanks for the heads up about the chuck jaws. Makes semse to me!
I had a 3" chuck that would have been easier the mount than the 5" one but it was just too small for my needs.
Thanks!
Russ

[Flybynight]

If you are seeing "light" under one jaw.
Did you open it up and make sure the jaws are installed correctly?
Just a thought.Jim

[torker]

If you are seeing "light" under one jaw.
Did you open it up and make sure the jaws are installed correctly?
Just a thought.Jim

Jim...I'm not quite following you. If the jaws where not installed properley there would be a considerable amount of runnout.
Don't ask me how I know this
Russ

[muddstopper]

A lot of replies since I was here yesterday. I havent done anything YET. As for the question about daylight, yes I did check to make sure the jaws where, for lack of a better word, threaded right in the chuck and that they where in the correct slot. I think Harold may have unknowingly found what has caused the problem in the first place. he mentioned a crash where an object was thrown from the chuck. When I first got the lathe, I did chuck in a 2 in peice of pipe and I did have it thrown across the room. I had tighten the chuck so hard that it had actually crushed the pipe where the jaws made contact. When I turned the lathe on it sent the pipe flying. I think it would be safe to say this is probably what has caused my problem. Now how do i fix it? I am guessing that the number one jaw is badly sprung, hence the daylight, well not actually daylight but it doesnt seem to contact the material like the other jaws. The jaws are two piece. Another question, just in case I run across another chuck how do I determine if it will fit my lathe. This is an old Monarch 14in lathe with about a 1-1/2in spindle bore, maybe a tad bigger but I would need to measure to be sure. I aint close to the lathe at the moment so i cant just run outside and get the measurement. In case you cant tell from my post, I own a lathe, I aint a machinist.

[Bill Shields]

Any chuck will fit as long as the backplate fits the spindle nose...

So, the nose knows....

There are 3 commonly used types of noses used in the USA, and you lathe could have either:

Threaded - the chuck just screws on
Camlock (A or D) - the chuck has 3 or 4 (or more) posts sticking out the back that are locked in place with a 'key'
L - tapered with a square keyway and locking collar.

When you get a chuck, you just get the appropriate back plate to fit the lathe....

Clear as mud?

http://shopswarf.orcon.net.nz/chuckmt.html

[Harold_V]

There are 3 commonly used types of noses used in the USA, and you lathe could have either:

Threaded - the chuck just screws on
Camlock (A or D) - the chuck has 3 or 4 (or more) posts sticking out the back that are locked in place with a 'key'
L - tapered with a square keyway and locking collar.

As I recall, A lacks the studs, and is not a cam lock type spindle. The chuck or other accessory is typically held in place by SHCS's through the face of the device, but each share a similar, if not identical, taper that the D device enjoys for registering the devices properly.

No, I've never used one like that, but I recall that the W&S turret lathes were equipped with such a spindle where I worked in my youth. I was never assigned to them.

Harold

[Harold_V]

I think Harold may have unknowingly found what has caused the problem in the first place.

Heh! Not exactly unknowingly. You see a lot when you've been around machines as long as I have. You can trust me on this one----you're not the first guy to have something come out of a chuck. (Don't ask!)

Now how do i fix it?

This is where a careful inspection is the word of the day.

Take the jaws out and look at the slide area in the chuck body. Compare one to the other, paying particular attention to the one you suspect is damaged. It's highly unlikely the jaws will have any damage, they're generally well heat treated and have considerably greater tensile strength than does the body.

Look for irregularities in the slide area---a step, maybe a fractured area----what ever. If the body is steel, it's unlikely to be fractured, but it could be deformed. If that be the case, depending on how the chuck is built, you may just have to live with it. You may envision a way to press the slide back straight, using a heat treated well fitting object and pressing in a large press, several tons capacity. It's a long shot, all depends on what you find, if anything.

The jaws are two piece.

That may change, to a minor degree, how you go about grinding the jaws, assuming you do. If your chuck is built such that the top jaw makes contact with the material, but the portion that runs in the slide doesn't, all you have to do is place your spacer (the disc you'd use for grinding) in that area, then grind only the top portions until they all clean up. The same rules set forth earlier still apply, only the "kill the small area" would change, for it may not touch, and won't matter. Make sense?

That you have two piece jaws is really a good thing. If you get interested in using soft jaws, you're already there. If you're not familiar with soft jaws, and want to be, there's a long post I made a few years ago that addresses them well, and should provide all the guidance necessary for you to have a firm understanding on how to make them, and how to apply them. I could provide a link for the post if you're interested. The pictures that went with it won't be available any longer, but I could repost them if necessary. The new software wasn't compatible in that regard, so pictures, for the most part, have all been lost.

Another question, just in case I run across another chuck how do I determine if it will fit my lathe.

Bill has addressed that nicely. The only thing I'd add is that you should keep in mind the size of the hole in your spindle, and make sure any chuck you acquire has a hole in the chuck body no smaller than the spindle bore. Only is you mount an unusually small chuck would that be a consideration, however. If your lathe is an early Monarch, that's probably not much of an issue, but later machines can have larger spindle bores, and it would be a shame to lose the capacity, especially if you're inclined to run fairly large diameter pieces.

One more thing. Assuming the slide is damaged, and the damage is general in nature (not a sharp ridge, for example), the grinding operation we've talked about will improve the chuck drastically, even if you don't make any corrections on the slide.

If you do find it is sprung, only one slide, select the average of the sizes you intend (or expect) to machine, and set the jaws for the average. That way the amount of error you get from the jaw will be split evenly from top to bottom size, with a perfect (?? You know what I mean) fit in the middle. In the end, you'll be quite surprised how well the chuck runs as compared to how it is now.

If you're real lucky, and the damage is well spread between all three slides, which I really think it is (sprung chucks are not uncommon), the chuck will run beautifully when you're finished.

Don't get discouraged with this thing yet----

In case you cant tell from my post, I own a lathe, I aint a machinist.

None of us were born with machining knowledge. It happens I've spent more time in the environment than you have-----that's the difference. Otherwise we each put our pants on one leg at a time. What really matters is your attitude----and yours is healthy. Not everyone welcomes input as you do, and that's an ongoing problem for people like me that run their mouths overtime----it's not always welcome.

Thanks for putting up with me.

Harold

[Harold_V]

Harold...don't you ever sleep?

Lets say it like this. I welcome your phone calls from noon on, even at 3:00 AM, but it is always a kindness if folks don't disturb me between 4:00 AM and noon.

We're both night people. By choice, we stay up most of the night.

The socket head screws...my thoughts exactly. I've already made some extra long T-nuts for the slots and had planned on using 1/4" screws.
The 1/4" adapter plate'll be turned and trued from 3/8" plate.
Thanks for the heads up about the chuck jaws. Makes semse to me!
I had a 3" chuck that would have been easier the mount than the 5" one but it was just too small for my needs.
Thanks!
Russ

Sounds like you have the thing firmly in hand. Should turn out great. The thinner plate (mine is 1" aluminum) makes for a little more space under the spindle. By the time you add a rotab and chuck, you often have very little left. A quarter inch can spell the difference between success or failure.

I used to have a 3" three jaw----bought it with my little Craftsman lathe when I was a boy. Nice little chucks, but quite worthless when you have some serious work to do. Might be nice to use under certain circumstances, though, like small work. You made a smart decision to go with a larger chuck for general purpose. Not only for holding larger items, but for holding power. The small one would likely let you down when you least expected. They're not very strong.

How about a picture when you're finished?

Harold