Lathe chucks which one and why (3 vs 4 jaw vs grip tru)

[Aaron_W]

So re-reading the first post, I think a lot of us may have over looked the real question. Not 3 jaw vs 4 jaw, but paying extra for a set-tru 3 jaw, if you own a 4 jaw.

So from that perspective, I think you need a set-tru when you get to the point where you need one. I'm not there, so I don't have one.

 

[higgite]

Gavin @ Ultimate Reloader did a review and explains it here:

That's interesting (and new to me), but I thought the OP was talking about different types of chucks, including set-tru models, not a separate spindle attachment to align any type of chuck in the Z-axis.

Tom

 

[mksj]

Concentricity does matter if you are not parting off the finished piece, if doing multiple ops then the time saving is significant with a 3J Set-Tru type of chuck. They each have their strengths, I often use a combination chuck which is a scroll with independent jaws, which allows much quicker ability to get parts in/out of the chuck and when necessary to dial down the last bit of TIR for high accuracy work. But for the majority of my turning I use the PBA Setrite 6" scroll chuck, because it is quick and accurate regardless if I am parting off or doing multiple ops. on the same piece. The PBA Grip-Tru chuck is an obsolete design and was replaced with the PBA Setrite once the Buck patent expired. The other difference I often see between 4J independent chucks and 3J scroll (at least the better made ones) is that the jaw tips are narrower and one tends to have less Z-axis skew. So both the ability to hold smaller stock, as well as not cutting a slight taper, a 3J scroll in my experience tend to be better.

It is a matter of preference, may people want one chuck to leave on the machine, for many a 4J independent is more versatile in that respect, and it is also a factor of cost. But often when buying lathes they come with both, and most people would probably get a 3J scroll (non Set-Tru) before they would get a 4J independnet.

The True Bore Chuck Alignment system adds an adjustment for axial adjustment, Set-Tru types are radial only. As noted, although it is only radial, they tend to have very little axial skew in my experience, much less then my 4J indepenennt chucks. My 8" combination chuck probably has the least axial skew of all my chucks.

 

[mfendley]

That's interesting (and new to me), but I thought the OP was talking about different types of chucks, including set-tru models, not a separate spindle attachment to align any type of chuck in the Z-axis.

Tom

You're right - I got the Set Tru and True Bore combined in my head somehow.

 

[cooper1203]

i was comparing all chucks.

on a job that requires removal of the part surly it only has to be dialed in once as to remove it requires 2 jaws to be loosened then when tightened the opposing two jaws are a reference providing the clamping diameter hasnt changed

 

[mksj]

Given variations in clamping pressure, I still recheck the TIR when reinserting a part. My Bison 4J combination chuck is a good example in that once dialed in it will repeat to around 0.001", but there can be slight differences in the clamping pressure, 3J they are equally distributed and has a lower repeat TIR with the Set-Tru type. The other component is that with multiple ops on a part, in my applications I am clamping different places on the part diameters, and readjustment of the 4J independent chuck would be very time consuming and cumbersome. Most 4J chucks do not holder smaller diameter work very well, I do use mine primarily for larger diamter roughing turning of hot rolled stock. It all depends on the type of turning work one is going to do.

 

[G-ManBart]

I would point out that there are now some very affordable set-true style 3J chucks that perform beautifully. I've put San Ou adjustable structure 8" and 6.5" 3J chucks on three or four lathes in the past two years and have had zero problems getting them to under .001" runout that's repeatable (same size stock of course). I think the 8" is around $250 or so now, so definitely not expensive. I say that also owning Buck, Bison and Pratt Burnerd set-true style chucks as well so I'm comparing against known good quality chucks (my Buck chucks are all made in the U.S. versions).

For most things I do .001 isn't going to make any difference so I can remove a part if needed, put it back in and still be fine. If it's really critical I break out the 4J and indicate the part like I should.

I actually somewhat disagree about the time factor. I have a day job, and when I have time to work on a project at home I'd rather not spend much of it dialing in a part if it's not necessary.

Something not mentioned is that a 4J isn't going to work with hex stock.

 

[talvare]

As a retiree and a hobbyist, I'm in that camp of time not being a big factor and I'm usually more concerned with getting the best accuracy I can at my skill level. I haven't mounted my 3-jaw chuck on my lathe in several years. I have a nice 8" Rohm 4-jaw combination scroll/independent chuck that is used pretty much any time I'm machining something that won't fit in my 5C collets. Since I use the 4-jaw frequently, I've gotten to where it really doesn't take very long to dial in a part, so I think, why not. I do also have a 6" six-jaw, set-true chuck available when needed for thin wall material, but it doesn't get used very often.

Ted

 

[RickKr]

Ooooh...you just made a slip up there.

Either you just revealed your membership of the small group of immortal human beings existing on earth, or you just admitted to being a sentient true AI!

Of course time matters. Everything takes some amount of time and whilst hobbyists aren't under commercial pressure, we can't spend 24/7 in the workshop and have other demands on our time.

Also eventually we get to the stage where, if we're lucky we, as Mr Pete so charmingly says, 'take a dirt nap', or we get decrepit enough that we can't use our workshops anymore.

You use a four jaw chuck where you either need to ensure concentricity if you have to remove the workpiece from the chuck, or you need absolute assurance that you have absolute minimum runout that a standard three jaw can't offer, or you need to hold a square part in the chuck (you can square up a piece of stock in a lathe with a four jaw chuck, if you don't have a mill), or you need to turn a feature that is eccentric to the lathe's spindle axis.

You'll use a three jaw chuck for pretty much the rest.

People say "If I was on a desert island and I could take only one chuck it would be a four jaw" and what they're actually saying is that a three jaw has limitations and just having a three jaw chuck is not enough.

And that's correct; everyone should have a four jaw chuck as a basic part of lathe tooling.

But no hobbyist, least of all beginners like thee and me, should be punishing themselves by having to dial in a workpiece in a four jaw chuck, every time they need to do a set of operations on a cylindrical workpiece where it can remain in place throughout those operations.

This really captures my perspective.

I learned machining, as a young man in college, in my father's shop, where we used all the types of chucks discussed and I learned dialing in 4-jaws and adjustable chucks. As a much older, hobbyist, I have no real time constraints and I just simply enjoy dialing in the adjustable chucks and I do it when I have to on 4-jaws. I have a couple of non-adjustable 3-jaw chucks but hardly ever use them. I have two adjustable Bison chucks, 8", 3-jaw, 5" 5C collet chuck and just sold a 5", 6-jaw Set-Tru Bison. The chuck I use preferentially is a 6", 6-jaw Adjust-Tru Buck, which came out of my father's shop. The 4-jaw chuck only gets used when there is a rectangular piece to be worked on. All these on a Monarch 10EE.

When I had a minilathe, I made an adjustable backplate for the 4", Bison 3-jaw that I had, following an article from a Home Shop Machinist article. I currently have Craftsman 6" lathe that I have an import 4" 6-jaw that I plan on making an adjustable backplate for, just because I like adjustable chucks, but also to allow correction of inherent runout of the spindle.

 

[WobblyHand]

For smaller stuff I use an ER-40 set true chuck. I really like using it. For bigger stuff, or rectangular stock, I use a four jaw chuck. I'm not as speedy as some setting it up, but eventually I get it dialed in.

Most of the time I use the ER-40, occasionally I use the 3 jaw. Rarer yet, the 4 jaw. But I'm glad to have a 4 jaw, because sometimes that's the only way to get it done.