Truing up jaws in lathe chuck

[Harold_V]

Yes I do agree in the real world 3 jaws are very nessary to make $$$, my point was that for us hobiest the 4 jaw has a lot usefullness, in getting better percission.

True!

I've taken note that some folks really struggle with using a 4 jaw, but it's not hard at all. One of the things that makes it easier is to pay attention to jaw location. The concentric rings on 4 jaw chucks are there to aid in doing so-----and the jaw as it relates to the OD or ID of the chuck is yet another way, although not quite as precise.

Are theres souces out there to get soft jaws for alot of the old chucks us hobist have

It's somewhat unusual for one to purchase soft jaws, although I'm sure that those that are in production with CNC machines are likely to purchase them instead of making them. Problem is, as you've noticed, the home shop chucks tend to come with two sets of jaws, neither of which will accommodate conventional soft jaws. In order to mount the typical soft jaw, the chuck should be equipped with master jaws, or two piece jaws. The soft jaw mounts in place of the top jaw, and is easily made from flat bar steel or aluminum.

And soft jaws typically machined the dame way with a disc clampted in the back and then the high spot ground off after?

Depends on the job at hand. Soft jaws aren't always bored through. It's desirable to bore a step, or counter bore, which matches the part in question. That way, when a part is inserted, it is automatically registered for square, and makes working lengths dead easy. One can work from an indicator or DRO, having already established a reference point. Keep in mind that this is a production method, but is very useful for the home shop type, particularly if the project at hand requires more than one piece. I offer, for example, machining a set of wheels for a locomotive.

Assuming one wanted to bore a set of straight jaws, as long as the soft jaw is somewhat below the surface of the master jaw, the spider, or ring you speak of, is placed behind the soft jaw, on the master jaw, so the soft jaw can be through bored. I use jaws like that in my chuck. Once bored, even though they don't necessarily fit the material in question, they are far superior to the factory jaws in precision, and will drive the material under all but the most severe of conditions. I rarely use the factory jaws.

Here's a link to a thread on a different forum, where a person has made soft jaws for a conventional chuck.

http://www.homeshopmachinist.net/bbs/sh ... =soft+jaws

I highly recommend you read the entire thread and glean some ideas on how you can pursue the use of soft jaws without buying a new chuck. I also highly recommend that if you try the idea, that you make jaws that are a snug fit over your hard jaws, and can be bolted securely so they can't come off under speed. That's easily accomplished by milling a slot in the soft jaws, which then goes over the hard jaw much like a stocking. The bolt would not have to go through the hard jaw, just above it.

I only have hard jaws in all fothe chucks I have, one trick i use a lot is to make a alunimum ring of 6060-T6, saw a spit in it and clamp the part through the ring. This protects the suface under the hard jaws fom damage and usually grips fine for lighter cuts, drilling and boaring.

Only problem is that it does little to improve running accuracy, and nothing towards registering the part. Soft jaws are a huge improvement over that method, and can be used for roughing operations as well as finishing operations.

It is generally desirable to re-machine the soft jaws after the roughing operation. That way the jaws match, perfectly, the finish diameter(s), and have a clean surface that won't mar the work piece. Note that it's important to work to a specific size, so the soft jaws will perform as desired. Holding the diameter to ± .001" is usually close enough, and increases one's skill level considerably by doing so.

I have also used the slpit ring to grip hex stock in round collets and the like with very good sucess. The aluminum really grips the hex stock good and dose not bur up the edges of the hex, even when the hex is brass.

That idea is common in the job shop, and not only for hex stock. It's a good trick for round stock, too, when the proper collet may not be at your disposal, and time doesn't allow for the purchase of one. It's not usually necessary to split the bushing (ring), assuming it is thin walled. The number of jobs I've run that way would be hard to count. Again, precision plays a role. All the parts must be of uniform size for the unsplit bushing, or ring, to work. If they vary widely, splitting is often the only option. My work habits were such that I could use one that wasn't split.

If you're interested, I posted a few years ago on soft jaws. There's a lot of good information in the thread, so I'm providing the link for your perusal. Hope it sheds some light on the use of soft jaws for you.

http://www.chaski.org/homemachinist/vie ... php?t=4266

Harold

[10 Wheeler Rob]

Harold,

Thanks for the info, I have only been surfing aorund this site for a coupleof months now, and still finding a lot good stuff tucked away under one topic or an other.

I have made some spit rings with a offset step in the back and a lip on the OD in the fount. This allows the part lip to seat on the lathe chuck or collet jaws and the part to seat at the botom which indexs the part location.

My reason for bringing up the aluminum insert idea is based on the fact of how happy I have been in the results of not damaging parts I am holding with its use and thought other novices like me could find it a cheap and useful method.

The hard aluminum machines up so easy to good acuracy and surface finish.

I have a semi pressous metals scrap yard just down the road form where I work, so i carry the AL out at $1.00/ lb. and take the scrap back at $0.50/lb. So it onl;y cost me pennies to make these convient aids.

Rob

[Harold_V]

The hard aluminum machines up so easy to good acuracy and surface finish.

Indeed it does! Knowing now how you get your material, keep an eye open for 7075-T6 as well. It's even harder than 6061-T6, and has a tensile strength that rivals mild steel. Machines real pretty, almost impossible to get it to tear.

I have a semi pressous metals scrap yard just down the road form where I work, so i carry the AL out at $1.00/ lb. and take the scrap back at $0.50/lb. So it onl;y cost me pennies to make these convient aids.

Rob

That's a killer good deal on aluminum these days.

I remember all too fondly the days when I had the run of a material supply house, where I was permitted to roam the entire warehouse looking for rems.

Price? 75¢/pound, for both aluminum and stainless.

Very heavy sigh!

I'm afraid those days are gone for ever.

Harold

[Conrad_R_Hoffman]

Checking in late on this thread, and after too much fine WA Riesling...

I disagree with most everything. I don't want curved surfaces on my jaws and I'd never finish them in the chuck. For the ancient chuck on my little Logan, I disassembled it, cleaned it, and put it back together. Then I chucked up a 1/2" ground rod and measured runout in line with each jaw. Entered that into a simple spreadsheet (because I make a lot of mistakes) which gave me the amount to grind off two jaws. Took 'em to work and set 'em up in the little Harrig surface grinder. Removed what the spreadsheet said. I think I gave all three jaws a tad of toe in. Put 'em back in the chuck and checked again. Ran within a thou or better. Minimum material removal, runs true, and grips well.

[SteveM]

Here's what I've been working on for sort jaws (with assistance from Harold).

These will fit on the outside jaws, as I'm making them to grip 3" loco wheels to re-bore the center holes.

The groove holds the jaws side-to-side and the screw at the end clamps it against the jaw.

Steve

[Harold_V]

Checking in late on this thread, and after too much fine WA Riesling..

I disagree with most everything. I don't want curved surfaces on my jaws and I'd never finish them in the chuck.

I'd fire you on the spot! (I've run a shop for gain----you'd be out of there instantly).

Blink. Blink.

Why? Are you playing the Devil's advocate?

Are you suggesting that journeyman machinists don't know what they're doing? (Not me----those that actually work for a living!)

Do you realize that the method I suggested is what is being used even today with CNC machines? It's not some fly-by-night fix, it's the best way to get a chuck to run properly, and usually adapts perfectly to the job at hand.

For the ancient chuck on my little Logan, I disassembled it, cleaned it, and put it back together. Then I chucked up a 1/2" ground rod and measured runout in line with each jaw. Entered that into a simple spreadsheet (because I make a lot of mistakes) which gave me the amount to grind off two jaws. Took 'em to work and set 'em up in the little Harrig surface grinder. Removed what the spreadsheet said. I think I gave all three jaws a tad of toe in. Put 'em back in the chuck and checked again. Ran within a thou or better. Minimum material removal, runs true, and grips well.

Yep! There's always more than one way to skin a cat, but there's usually one way that's far better than the others. That's the case in this instance.

Could have done it in the chuck body and got them to run dead perfect at a given diameter. That's not a very good way to grind jaws, although it does work to some degree. Problem is, it doesn't address one of the biggest problems with chucks, that being the springing of the body. How can you properly compensate for that?

You've likely noticed your chuck doesn't run the same as you change diameters. There's usually some wear on the scroll anchor, and error in the scroll, considering they're rough milled than heat treated. Older chucks may not have been ground, either. Hard to say.

Mind you, I'm not arguing with your method, but it's subject to hit and miss. You already said that it runs within a thou-------that wouldn't be acceptable to me with soft jaws. They will run within a half thou routinely, and closer if you care to spend a little extra time. They'll do that on any diameter, too, unlike hard jaws.

However, the most important feature is that you can grip parts and register them perfectly--almost instantly---time and again----- which you can't do with hard jaws. Further, they don't mar your work, again, unlike hard jaws. There's lots of good reasons to use soft jaws------so if you aren't familiar with them, I'd strongly suggest you reserve judgment until that time that you've tried them. You might be pleasantly surprised to find you won't use those hard jaws much that you spent time repairing once you've tried them.

Don't be contrary just for the sake of being contrary. Try soft jaws, then form an opinion.

Harold

[Conrad_R_Hoffman]

Hey, you would have fired me long before I ever got near the chuck! I just recently talked to a guy who would have fired me for using a grinding vise on the mill- started talking about sin or something...

No question soft jaws are a whole 'nuther story. Obviously they should be trued in situ, and should run almost perfectly for the job. My old Logan chuck jaws are hard as glass, there's certainly some scroll wear, and replacements, hard or soft, probably won't be found in this lifetime. When the jaws were new, they had narrow flats. To keep those flats relatively flat one would grind the jaws wide open. Due to the scroll wear, that isn't where I'd want to grind them, plus they'd be less stable. Close 'em down and you end up with a small radius curved surface that dings each contact point twice on large work. Not something I find desirable. So, yeah, I have reasons, logical or not, but mostly I just like to be contrary- keeps people thinking

[10 Wheeler Rob]

Reguarding rebore of loco wheels, why ot just clamp them to a surface plate, lightly clamp, tap into true position using a dial insicator and tighen & recheck run out and rebore form there.

Its a lot quicker then makin tooling, I aquired a 8 1/2 inch palte for my late with tee lots and aobut 100 taped holes, it will hold alsmost anty thing with ouut having tomake a lot of tooling.

rob

[SteveM]

I could do it that way, but I think that soft jaws will ensure concentricity better. If I used a plate, I would probably want to take a light cut on the treads to be sure they were true. Since I think I did a good job on the treads, I'd rather not chance messing them up .

Besides, I can re-use the soft jaws for other things.

Hey, 10 Wheeler Rob, you going to the meet at PVLS this weekend? I'll be there on Saturday.

Steve

[10 Wheeler Rob]

Yes, I will be most of the week end, I joined this sping. Are you a member there or with another club? You have an engine to bring or is this the first you are building. I tell you to look for gray hair and beard, but thats about 1/4 of the club, LOL.


Rob

[UnkaJesse]

The enclosed photo shows a fixture I made to re-grind all of my three jaw chuck jaws. Actually it is on the chuck backwards in the photo, but I had to put it on like that for the photograph. Normally the three pairs of keystock pieces would be against the chuck face and exactly how the device works would have been concealed' To use it is mostly obvious, but I will explain anyway.

The jig-fixture-tool (whatever) is placed onto the chuck jaws which have been opened sufficiently to admit my grinder wheel, the Allen bolts are tightened snugly against the chuck jaws and the chuck tightened a bit. This puts a proper strain on the jaws just as if they were clamping a round piece of stock. My heavy duty Craftsman hand grinder, (Yes honey, at one time 40 years ago Sears sold industrial quality tools, but no more ) is clamped on my tool post and the grinding commenced. Since the strain on the jaws is in the proper direction, the grinding straightens them up as well as can be expected of a 30 year old heavily used chuck. As Harold said, they will only be close to accurate since the wear in the scroll will not be even. Most of my work has been high speed turning of small parts in 12L14 steel, so it is plenty accurate enough for the job.

Oh, gee, look at the crud on the front of the headstock. Some of that probably dates back 30 years. Please don't anyone admonish me for that as it fits right in with the rest of my shop as Keith Spriggs will testify. If it was wiped off, it would be out of place amongst the other crud scattered around. At least the ways are kept clean and oiled.

As an alternative to a fixture like this, if each jaw had a hole drilled in the face at the factory, short pins could be put into those holes and the chuck tightened down on a ring. Results would be the same as truing them my way. Hey, maybe I need to get a patent on "holey chuck jaws"?

Just noticed that I need to explain that the fixture openings seem too wide for the chuck jaws and they are. I milled the openings out to use on one of my other chucks which has MUCH thicker jaws and to use it on the small chuck, I have to insert three keystock spacers or get longer clamp screws. Too cheap to buy longer screws so I use scrap pieces of keystock.

Unka Jesse

[Bill Shields]

Hey Jess:

For the small stuff...ever heard of that wonderful device called a collet? Available in a multitude of sizes, runs quite true, can be had in round, hex, square....there's a little company up in Horseheads NY that makes a lot of them...Hardinge I think they are called...U might try looking them up.

I have one lathe that LIVES with collets in it all the time...very rarely sees the chuck.

I use a truing ring that has pins that fit in the mount bolt recesses of the top jaws..allows me to 'clamp down' like your rig...mine is set for 1-1/2" or thereabouts...a diameter too big for my collet machine.

Anything much larger than that, if the scroll is out, the 4 jaw gets it because it is something that I do so rarely that I don't care about efficiency.

This is a hobby site and we are supposed to be innovating and sharing solutions to common problems...

I have seen several new 'bents' on how to skin this cat that I would not have thought of because I had mild tunnel vision..my way worked and I didn't think of other ways...that turned out to be just as good if not better than the way I had been doing it.

Imagine THAT! Somebody ELSE had a good idea. Unique.....