Can anyone explain non-independent 4-jaw lathe chucks to me?

[gellfex]

Can someone explain how non-independent 4-jaw lathe chucks are useful if any eccentricity in the stock leaves only 2 jaws tight and the other axis loose? I don't get it. Where are these advantageous over 3 jaw or independent 4 jaw?

[Toolguy]

I like them for milling more than lathe. I use them flat on the table facing up for longer round or square parts on end or on the rotary table in vertical mode with the part parallel to the mill table. I have never had a problem with only 2 jaws tight. They work fine for me. It is a fast way to do multiples of the same part because you only indicate it in for the 1st part, then it repeats for all the rest. i think they hold tighter with 2 opposing jaws than a 3 jaw with jaw opposing air and way quicker and easier than an independent 4 jaw.

[10KPete]

Not everything that goes in a lathe is round. A lot of work is square.

Pete

[chipmaker4130]

Not everything that goes in a lathe is round. A lot of work is square.

Pete

That is the problem! If the stock isn't a perfect square, but the chuck is 'right on', one set of opposing jaws won't tighten. Same issue as with a 3-legged stool and one with 4 legs, either one on an uneven floor. Three will not rock, four will. Odds are very good that you'll need to singly adjust one jaw of a scroll-type 4-jaw chuck with every variation of stock or part. Then, when the scroll wears, it won't latch on to perfectly round or square stock either without a similar adjustment.

I think they are intended to be 'set up' for each job and then working multiple identical, odd shaped parts, or the same part in and out of the chuck. I'm not aware of any other advantage.

[danlb]

That is the problem! If the stock isn't a perfect square, but the chuck is 'right on', one set of opposing jaws won't tighten.

Then think of it as being like a vice. If only 2 jaws are in firm contact, then it's still making better contact than 3 jaw. A 3 jaw chuck will make contact with the middle of side one, and at the corners of side 2-3 and corner 4-3. It will be unbalanced.

A rectangular piece is not a good choice for a 4 jaw scroll chuck on a lathe.

Dan

[Rich Carlstedt]

Not intended for non-symmetrical stock !
Mostly used for square stock and tubing
It allows rapid workpiece changes with such material
More jaws cause less distortion of the work and result in less marking.
You would not chuck square stock in a 3 jaw, and should not chuck uneven stock in a
non-adjustable "Universal 4 jaw" chuck

Rich

[gellfex]

So far, the only argument "for" the scroll 4-jaw seems to be it's faster to change reasonably accurate square stock than an independent 4-jaw. Seems a stretch. In the latter I simply designate and mark 2 jaws to loosen and tighten while changing stock after I've indicated it.

[janvanruth]

imagine having to do simple,one off, work at consecutively: round 2 inch, square 2.5 inch, round 1.25 inch, square 1 inch.
Now you take your independent 4 jaw and i will take the scroll 4 jaw.
Guess who will be finished first.

[J Tiers]

Never seen one of those. All the ones of the type I have seen have BOTH. A scroll, AND independent adjustment. That way you set up as 4 jaw, and then every time you put a new piece in, you use the scroll. Acts like an adjust tru, but has a lot more range, and can hold round, square and irregular (OK not so good on triangular or 6 side).

[Doozer]

Use them to hold taps.

-D

[PStechPaul]

When I first bought my 9x20 lathe, I realized that I needed a 4-jaw chuck, so I bought an 8" 4-jaw scroll chuck. and an 8" adapter plate. But there were problems. (1) an 8" chuck really does not fit well on a lathe with 9" diameter swing, (2) it was useless for rectangular stock, and (3) the adapter plate was not made for a screw-on spindle as I had. I really didn't know enough to realize my mistakes. So I traded the new 8" scroll chuck for a 6" Cushman independent chuck that needed repair, bought and machined the proper adapter plate, and traded my 8" backing plate for other things I could use.

[CalM]

I would take a four jaw scroll chuck if it were given to me, but I wouldn't go buy one unless a job using square or octagonal stock came my way. And even then, in the smaller sizes, I might look at 5C collets, or machined soft jaws on the 3 jaw before hunting up and mounting a 4J self centering chuck.

[Arcane]

I have a 4 jaw scroll chuck that I often use on square stock and occasionally on round stock. Strangely enough I have never had any stock come flying out of the jaws, not even once, and the finished turning was exactly what I wanted it to be. How amazing is that!?

[lakeside53]

I have one of the scroll+independent. Fabulous... my favorite chuck.

[Forrest Addy]

All lathe spindle tooling has a purpose, a niche in which it performs particularly well. Scroll chucks, independent chucks, collets, dead centess, pots, spuds, faceplates, etc each with their particular purpose and some nearly universal.

If your work load is mostly round and you never need to work to close tolerances, or never need to get a death grip on a work item for heavy roughing, or never need to grip odd shaped parts you'll probably chances are you'll never need a four jaw chuck.

Four jaws chucks do have their place. They really are universal, grip better, and can be dialed into whatever degree of concentricity the job warrants. If you ever have to work in a manual machine tool job shop where you're expected to run large lathes and vertical boring mills, you better be able to work with four jaw independent chucks.

Tak a look at this video:

https://www.youtube.com/watch?v=0IStp69jcJU

where Adam Booth dials in round work on a four jaw chuck is a minute or so. Look at some of Abom79's videos where he runs larger lathes and you'll see a job shop machinist who knows his stuff and makes is boss lots of money - and he does this in part because he's practiced and efficient with a chuck key.

many of you will never need to work up to this standard on a four jaw chuck but knowing the rudiments of it's efficient use is an inescapable qualification for employment in a general or a jobbing machine shop.

My advise is to not declare against using a four jaw chuck until you get a little practice. If you're serious about learning the use of an engine lathe you really do need to skill with the four jaw chuck. If you have the time it's important to learn this new skill in small bite. Work with it until the frustration kicks in then do do something else. Sooner or later will come a breakthrough and dialing in a four jaw suddenly gets easier.

Here's a couple video to get you started. .

https://www.youtube.com/watch?v=HSjQfnXuhEE

https://www.youtube.com/watch?v=aA0suYN72SE

Be patient, these two guys really know their stuff but they are not teachers so they tend to babble about trivialities and wander off the subject. If you want a few other perspectives get on YouTube and type in "indicationg a four jaw chuck." There's tons of stuff including some utter BS

Story: Back in the old days when I was serving my time, us apprentices were rotated two two month tours through the engine lathes. The first tour we had to use four jaw chucks of everything big and small. These were not the tight accurate chucks the better lathe hands used. These chucks dated from Noah's arc and were so loose when you spun them empty the jaws clattered in the clearances like castanets. Worn really didn't matter. After a week or two of hell's kitchen supervision, we got so we could tweak work into a half thou.

As we gained skill were were tested against a watch eventually dialing in a globe valve body to the seat bore and the bonnet flange face. This represented typical work on an engine lathe in a naval ship[yard and there were plenty of valve bodies on hand for the test. It was a tougher job than simply dialing in a hunk of round stock. One pair of jaws gripped the line flanges and the other pair gripped the body. You had to pad the jaws on the line flanges so you didn't make them and you had to be careful not to bend them by muscling the chuck key.

Usual times for experienced lathe hands ran a couple of minutes. Us apprentices were allowed five. You couldn't get it in five try again next week, no blame, no stigma Try til you get it. Took me a couple of tries and I thought I was a hot shot.

We had to dial in round work too as a preliminary but we didn't graduate to three jaw chucks, collets etc until we mastered the four jaw chuck. Over the years people I used to work with would borrow my lathe for some project. Most retired as senior supervisors and bureaucrats. Even after 25 years of pushing paper they could still efficiently dial in a four jaw chuck - much to their surprise and gratification. Dialing in a four jaw chuck must be a life skill like riding a bicycle.