3-jaw set-tru vs 4-jaw universal chuck

leeko · Jul 25, 2018

Hi everyone,

Given the choice, would a 4-jaw universal scroll chuck be more or less desirable than a 3-jaw set-tru for a general use manual lathe?

I used a 16" 4-jaw universal (scroll plus independent) chuck on my Lodge and Shipley, and I really liked it but it was pretty worn and I found I pretty much needed to dial it in every time I chucked something. I now have a smaller 10", better condition version of the same, but haven't used it yet. I also have a set-tru 3 jaw of similar size. Haven't bought any L0 backplates yet, and am wondering which one to start with. I'm thinking the 4-jaw because it can chuck non-round pieces, but wondering if there are any disadvantages I haven't considered? They'll bith eventually be going on a 14" Celtic (Mondiale) lathe.

Thanks,

Lee

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billzweig · Jul 25, 2018

I was never too impressed with the 3-jaw set-tru chucks. All else being equal a 4 jaw independent is my first choice when there is a need for precise centring.
I have a number of good quality self-centering chucks in various sizes and of 3, 4 and 6 jaws. On all of those I did grind the jaws in place (external and internal as well as the jaw faces) and with the lathe spindle and the chucks marked for installation in same position. I can get a decent results repeatable at all diameters of about 10-15 microns run-out.

L Vanice · Jul 25, 2018

A universal chuck is usually understood to be a self-centering chuck with no independent feature on the jaws. Scroll chucks are universal, but some early design universal chucks do not have scrolls. Some universal chucks have a centering adjustment that moves the chuck body with respect to the adapter plate or a separate rear part of the chuck body in order to get the jaws to run true. Those are adjustable universal chucks and each chuck maker had their own trade name for them, Buck's Ajust-Tru being well known. Either type of universal chuck has been made with 2, 3, 4 or 6 jaws. The Swiss have made 8-jaw universal chucks without the adjustment feature.

A self-centering chuck with independently adjustable jaws is usually called a combination chuck. I have two NIB examples from German makers that call them System Wescott on the box, presumably a misspelled version of Westcott, an American chuck company that may have invented the style in the 19th Century.

I have a Swiss-made 4-jaw combination chuck and like it, but do not use it for everyday jobs. Those are done on Pratt Burnerd Setrite adjustable 3-jaw and 6-jaw universal chucks.

Westcott Chuck Co. history and patents: Westcott Chuck Co. - History | VintageMachinery.org

Larry

thermite · Jul 25, 2018

leeko said:
Hi everyone,

Given the choice, would a 4-jaw universal scroll chuck be more or less desirable than a 3-jaw set-tru for a general use manual lathe?

I used a 16" 4-jaw universal (scroll plus independent) chuck on my Lodge and Shipley, and I really liked it but it was pretty worn and I found I pretty much needed to dial it in every time I chucked something. I now have a smaller 10", better condition version of the same, but haven't used it yet. I also have a set-tru 3 jaw of similar size. Haven't bought any L0 backplates yet, and am wondering which one to start with. I'm thinking the 4-jaw because it can chuck non-round pieces, but wondering if there are any disadvantages I haven't considered? They'll bith eventually be going on a 14" Celtic (Mondiale) lathe.

Some folk find a combination chuck the best of both worlds.

I'm the reverse. Separate chucks that each do only ONE thing will do it better and with greater strength, same mass of metal, or close-to, and generally for less total cost over time, acquisition, repair and eventual replacement included.

That just might be why one-trick-pony chucks have always been far more common than combo?

Not as if you were going to TiG it to the spindle, is it?

PS: A 14" Mondiale Celtic should swing the same diameter nose-art as my HBX-360-BC, yah?

Any interest in a genuine FRENCH 3-J ("Handy") with two-piece top jaws in a standard and available mate-up? Came in as OEM on the Cazeneuve, and I don't like even having an apprentice chuck under my roof, let alone mounted.

CalG · Jul 25, 2018

The "Set-Tru really shines with easily crushable work pieces.

Four jaw chucks have rather course jaw movement screws and for small corrections, that often means just a little nudge of one jaw or the other against the fixed positions of the other three jaws. If you relax the opposite jaw, the movement is "too large".

The Set-Tru chucks have rather fine adjusting screws, and movement there does not result in a change of work piece clamping pressure.

I find the Set-Tru chucks easier to dial in to +/- .001.

An aside:

This afternoon I wanted to run up a small threaded nose piece in 3/4 inch brass. The purpose is to allow holding of an od sized threaded shaft in a 5C collet I have on hand. Nothing special or high tolerance.

I used brown paper to bring the stock to within .002 on the three jaw. It was a pretty rough piece, having been used for a brass knocker around the shop for some years. The chuck is actually better than that on good stock, but this stock needed help. ;-)

It cleaned up nice, and the cap came out just fine.

A 12 inch four jaw can try my patience, Chasing back and forth in pursuit of both centration and clamping.

thermite · Jul 25, 2018

CalG said:
The "Set-Tru really shines with easily crushable work pieces.

Point. My 6-jaw scroll is Tru-adjust or wotever Fuerda calls their version. Managing easily deformables (tubing, generally) is its primary reason for being here at all. AFAIK, a six-jaw scroll has LESS ultimate grip than a 3-jaw scroll on low-deformability stock. Some jaws might not be fully loaded - or even loaded AT ALL.

Four jaw chucks have rather course jaw movement screws and for small corrections, that often means just a little nudge of one jaw or the other against the fixed positions of the other three jaws. If you relax the opposite jaw, the movement is "too large".

The Set-Tru chucks have rather fine adjusting screws, and movement there does not result in a change of work piece clamping pressure.

I find the Set-Tru chucks easier to dial in to +/- .001.
.
.

A 12 inch four jaw can try my patience, Chasing back and forth in pursuit of both centration and clamping.

Might be worse-yet on the 20" and up I once lived-off of, but there you have it.

So long as I can reach end-of-life (mine, not the chucks) without having used a 3-J in over fifty years, I am simply oblivious to any 4-J hassle. It is what it is. Not really ever having known anything different, there's no problem hitting a thou, and it just isn't perceived as a hassle.

Forrest Addy · Jul 26, 2018

3 jaw set-tru chucks and 4 jaw independent chucks are intended for difference services.

The 3 jaw set-tru shines in second ops for a repeatable concentric grip on finished work and stock where semi-finish and final finish cuts are the rule. 3 jaw and 6 jaw chucks are delicate. It doesn't take much of a wreck to knock them out of whack: break a parting tool, that kind of thing. Just because you had a little wreck and re-dialed the work in doesn't mean you're out of the woods. If it dials in next to the jaws, does the work also dial in 4" out? It's surprisingly easy to spring a jaw.

4 jaw chucks can grip most anything in their range and, being simple and robust, hard to damage significantly. With a little practice and some mentoring it takes about a minute to dial in the registration feature of any odd shape part. OTH, if you have a dozen little fittings to face, drill, champher, and tap, a 4 jaw of any size or condition will be a PITA.

That said, I suggest mounting the 4 jaw. You can use it for anything and you can't really hurt it. When another back plate becomes available use that for the set-tru. When you get it mounted, treat it gently. 0.0005" concentricity is not something you risk by pushing the envelope.

Don't be put off by a worn 4 jaw. Worn or not, you can still split thousandths TIR but it might take a bit more time. When I was an apprentice (here I go, again) they made us do everything out of a 4 jaw and being apprentices, we got the dregs and we did the simple crude stuff. When we passed our time tests (dial in a part in one minute, make a complete 1" bolt and part it off in five, etc) we graduated to the better chucks and collets and were given more demanding work. Whoopee! but we cherished our little victorys.

projectnut · Jul 26, 2018

Forrest Addy said:
3 jaw set-tru chucks and 4 jaw independent chucks are intended for difference services.

The 3 jaw set-tru shines in second ops for a repeatable concentric grip on finished work and stock where semi-finish and final finish cuts are the rule. 3 jaw and 6 jaw chucks are delicate. It doesn't take much of a wreck to knock them out of whack: break a parting tool, that kind of thing. Just because you had a little wreck and re-dialed the work in doesn't mean you're out of the woods. If it dials in next to the jaws, does the work also dial in 4" out? It's surprisingly easy to spring a jaw.

4 jaw chucks can grip most anything in their range and, being simple and robust, hard to damage significantly. With a little practice and some mentoring it takes about a minute to dial in the registration feature of any odd shape part. OTH, if you have a dozen little fittings to face, drill, champher, and tap, a 4 jaw of any size or condition will be a PITA.

That said, I suggest mounting the 4 jaw. You can use it for anything and you can't really hurt it. When another back plate becomes available use that for the set-tru. When you get it mounted, treat it gently. 0.0005" concentricity is not something you risk by pushing the envelope.

Don't be put off by a worn 4 jaw. Worn or not, you can still split thousandths TIR but it might take a bit more time. When I was an apprentice (here I go, again) they made us do everything out of a 4 jaw and being apprentices, we got the dregs and we did the simple crude stuff. When we passed our time tests (dial in a part in one minute, make a complete 1" bolt and part it off in five, etc) we graduated to the better chucks and collets and were given more demanding work. Whoopee! but we cherished our little victorys.

I find it interesting you made the statement "Don't be put off by a worn 4 jaw. Worn or not, you can still split thousandths TIR but it might take a bit more time".

I have over a dozen chucks around the shop for various lathes. Most are the 8" to 10" four jaw variety and some show their age. Having said that for some reason the most used one for one offs is an old LW four jaw 10". The jaws are so loose they sounds like castanets, but it still can be adjusted to .0005". It should probably be retired, but for some reason it always seems to be the right size. Not only for holding the work, but it doesn't require 2 men and a boy to carry it around, and I don't need a crane to install it. With all its faults it still works for the one off jobs. I will admit it doesn't get used for multiples, whether it's 10 or 100. It would be just too time consuming to dial to in every part.

richard newman · Jul 26, 2018

No ones mentioned using soft jaws on a 3 jaw. Makes repeatability pretty much a non issue for multiple parts or something that has to be re-chucked several times.

thermite · Jul 26, 2018

projectnut said:
I will admit it doesn't get used for multiples, whether it's 10 or 100. It would be just too time consuming to dial to in every part.

In high volume, collet systems, ELSE power-actuated chucks have dominated that scene since forever-ago anyway - even before CNC.

Those are not out of our reach. Used-but-good market has equipped me with a 6" English-built-Hardinge branded 2-Jaw with commonly available top jaw blanks. Also a Walker-for-Hardinge 6" magnetic.

Used SMT, Kitagawa, Samchully, etc. and their air-operated actuators are out there as well.

A scroll-operated 3-jaw, in my experience, is a perpetual "third place winner" compromise, if-even third-place. As with the "combo" chucks, there are performance, durability, longevity, and strength penalties to be paid for their "convenience".

Everything those can do is better done with two or more alternative workholding systems.

Powered 3-Jaw that are NOT scroll-operated are a whole 'nuther universe, of course.

Those earn their expensive keep rather competently on serious tasking.

leeko · Jul 26, 2018

Thanks everyone for the input. I wasn't aware of the compromises a combination chuck involves...

I do have a complete Jacobs rubberflex collet chuck and collets that came with the lathe. Seems pretty nice, though I haven't played around with the hammer-tru technique outlined in the manual yet (!). Run-out was around 0.001" on an endmill close to the nose without any adjustment.

Bill, thanks for the offer but I'll have to pass. I have chucks coming out of my ears after a couple of recent auction bonanzas. I just need to pick a 3J and 4J to complement the collet chuck. I don't do enough thin wall stuff to merit a 6J, and I'm not even sure what a 2J is used for. No need for power chucks here, either - just puttering around with one-off things for the most part.

Thanks again

Lee

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thermite · Jul 26, 2018

leeko said:
I do have a complete Jacobs rubberflex collet chuck and collets that came with the lathe. Seems pretty nice, though I haven't played around with the hammer-tru technique outlined in the manual yet (!). Run-out was around 0.001" on an endmill close to the nose without any adjustment.

I have two, great for some things, PITA otherwise, the Rubberflex.

2-J. The obvious is obvious, pipe jaws for example, basically just the opposed Vee-block concept. I'd not have spent a dime for that capability.

The "value" in 2-J comes when you tool or fixture the top jaws or plates. ANY shape that you can find a way to work to a "parting" line, even one that doesn't really exist, can be gripped with very, very high repeatability.

Suppose you had race-track shaped castings to work with a standing boss offset to one end of it - much like an automobile transmission input shaft support casting. You need to turn the OD and bore the ID of that off-center feature. Bespoke plate, jaws, or sometimes just an array of dowel-pins, and the parts can be located clamped, machined, unclamped with no "dialing in" involved.

The alignment was done - once-only - when you crafted the top-jaws or top-plates.

In that sense, the 2-J is cousin to a tooled-up vise or bespoke fixture on a mill.

2JW

HuFlungDung · Jul 26, 2018

A 4 jaw combination is pretty much just a 4 jaw independent chuck: yes you have to dial it in every time. BUT, it can save you some time if you have marked the part, take it out and put it back in, as the jaws will be close to the proper place. I make extensive use of this for rechucking motor endbells for boring, sleeving and then boring again. But it's not a must have feature for an occasional user.

But one feature that is a byproduct of having scroll base plates and screws on the jaws is that you can get a fair amount of increased chucking capacity if you allow the jaws to overhang the base jaws a little and let the base jaws hang out of the scroll a little. This can increase your available holding options for awkward parts that are of such a diameter or depth that you'd maybe not have to reverse the jaws (to get better reach).

I believe at the time I got my Summit with the 4.125" spindle bore, that there was not many options to purchase a small 12.5" chuck with a through bore big enough to match the spindle bore (or could stand being bored out to match). That's the real reason I got the Rohm 4 jaw combination (and the 3 jaw combination as well). I never liked self centering chucks that lacked any adjustment hence my option to go for the 3 jaw combination. Yeah, the chuck might be .005" out every time you put something in, but you can fix it to zero if you like in a few seconds, rather than screwing around with shims and mostly settling for less than perfect as a result. But you don't absolutely have to dial a 3 jaw in every time, but a 4, you do have to tweak at least 2 jaws, and then things go to hell fairly quick on the next iteration

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