What's the primary benefit of the adjustable 3 jaw scroll chuck?

[skcncx]

A set-tru style one can adjust the TIR down to typically under 0.0004", and it should repeat within this range when you switch out the stock. The tolerance also should repeat within the scroll range,

With that the value proposition goes up a lot for me.

I have found myself flipping parts a lot on my Atlas 618 so I would like something on my PM-1236T that is as easy to use as a scroll 3 jaw but still hold good tolerances when I flip parts.

I did lookup a toolmex 6" 3 jaw adjustable, I think they were around $1300... so the PM one for $700 seems like a good deal, and for $50 you can get an extra set of jaws. PM also states it's precision balanced, I would think that is of benefit, especially for a smaller weight PM-1236T lathe (big for me though)

My 3J 6" scroll is a PBA Setrite with a single scroll pinion and it repeats very well.

Excuse my ignorance... but single scroll pinion just means there's only one spot on the circumference of the chuck to use the chuck key to clamp it down?

And, am I right, on these adjustable chucks, the way you indicate it in for less TIR, unlike a 4 jaw where you adjust each jaw independently, but rather use some screws on the face of the jaw to move it around? That's the impression I got by watching a tubalcain video. So, given the repeatability of an adjustable 3 jaw after you indicate it in, it's set it and forget it.... assuming it doesn't shift out of place.

 

[skcncx]

Lets not forget about boring soft jaws either .

So, is that like tru-ing up a 3 jaw chuck just by modifying the jaws themselves while it's turning on the lathe?

I assumed soft jaws were just for softer materials to not mark them and ruin any finish by clamping down on them.

 

[mmcmdl]

So, is that like tru-ing up a 3 jaw chuck just by modifying the jaws themselves while it's turning on the lathe?

Soft jaws are either aluminum or steel used for multiple parts requiring close TIR . Bore them to the finish size of your part . They are re-usable also , and can be bored for multiple set-ups . No , they will not mark parts .

 

[mikey]

Is this a correct statement? The primary benefit is when you plan to chuck the same sized parts and or need to flip a part and keep it concentric. The second you open or close the jaws too much for a larger or smaller part, you lose the benefit of an adjustable (scroll type) 3 jaw chuck where TIR was all but removed... and you are back to the characteristics of a standard, non adjustable 3 jaw chuck.

Unless you're in a production situation, the need to turn the same size stock repeatedly enough to justify a set-tru chuck is not common in a hobby shop. Most work is one off. Flipping a part and getting it concentric again is, however, a common scenario. This can be done with a set-tru or a 4jaw.

I own two set-tru style chucks - a very fine Yuasa 3 jaw and a mint Pratt Burnerd International 6 jaw. Both are adjustable into the low tenths and neither one is used all that much. 95% of the work I do on a lathe is first operations stuff so a simple 3 jaw is as accurate as I need. If I have to flip a part and tolerances are tight I switch to a 4 jaw, not a set-tru or a collet chuck.

There is nothing wrong with owning set-tru chucks. Just know that they are not all that necessary in a hobby shop.

If I'm tracking correctly, what's the tolerance for "same sized parts" in an adjustable 3 jaw chuck. In order to keep TIR very low between chucking different parts all have to be within a few thousandths? Or is it more like 1/2"?

Same means same. If your chuck is adjusted to minimize run out with a specific diameter then if the next part is of a different diameter then run out will increase. This has been measured and proven by many of us. How much pressure you apply to the chuck key, the amount of oil on the stock, and the specific pinion you use to lock the chuck down can also impact on TIR. This really only applies to second op work, most commonly applied to production runs. A collet chuck with a torqued nut may be a better/cheaper option.

I only raise these issues because of the expense of these chucks. They cost a lot of money and I'm not convinced they deliver all that much value in a hobby shop setting. My two chucks alone retail for almost $5,000 and are not used anywhere near enough to justify their cost. Quite frankly, a really good 3 jaw and 4 jaw chuck and a decent collet chuck for threaded or polished work will do most of us just fine.,

 

[Jimsehr]

Unless you're in a production situation, the need to turn the same size stock repeatedly enough to justify a set-tru chuck is not common in a hobby shop. Most work is one off. Flipping a part and getting it concentric again is, however, a common scenario. This can be done with a set-tru or a 4jaw.

I own two set-tru style chucks - a very fine Yuasa 3 jaw and a mint Pratt Burnerd International 6 jaw. Both are adjustable into the low tenths and neither one is used all that much. 95% of the work I do on a lathe is first operations stuff so a simple 3 jaw is as accurate as I need. If I have to flip a part and tolerances are tight I switch to a 4 jaw, not a set-tru or a collet chuck.

There is nothing wrong with owning set-tru chucks. Just know that they are not all that necessary in a hobby shop.


Same means same. If your chuck is adjusted to minimize run out with a specific diameter then if the next part is of a different diameter then run out will increase. This has been measured and proven by many of us. How much pressure you apply to the chuck key, the amount of oil on the stock, and the specific pinion you use to lock the chuck down can also impact on TIR. This really only applies to second op work, most commonly applied to production runs. A collet chuck with a torqued nut may be a better/cheaper option.

I only raise these issues because of the expense of these chucks. They cost a lot of money and I'm not convinced they deliver all that much value in a hobby shop setting. My two chucks alone retail for almost $5,000 and are not used anywhere near enough to justify their cost. Quite frankly, a really good 3 jaw and 4 jaw chuck and a decent collet chuck for threaded or polished work will do most of us just fine.,

A set true chuck needs a little slop to be able to set it true. You can also make a set true chuck by using a larger chuck back plate and counter boring it so that the chuck body fits into the counter bore with a little slop and 4 set screws to adjust it true. That way the chuck body is used as the register.
jimsehr

 

[skcncx]

I only raise these issues because of the expense of these chucks. They cost a lot of money and I'm not convinced they deliver all that much value in a hobby shop setting. My two chucks alone retail for almost $5,000 and are not used anywhere near enough to justify their cost. Quite frankly, a really good 3 jaw and 4 jaw chuck and a decent collet chuck for threaded or polished work will do most of us just fine.,

I think that's where the value of PMs adjustable 3 jaw chuck made in Taiwan for $700 is a good value. I was looking at non adjustable scroll jaw chucks from TMX and they are $1000+, I assume that would be a really good 3 jaw. I guess when I'm ready to upgrade, I'll look around but my guess is that I won't beat PM's adjustable 3 jaw scroll chuck.

 

[Ischgl99]

The 3 jaw that comes with the PM-1236T might be good enough for what you plan on doing. When I got mine, it was 0.005-0.007” out, and I was not happy with that. Disassembling it and cleaning did not help any, but after using it a bit, it is now 0.001-0.003” depending on the diameter and whether using the inner our outer jaw surfaces. I suspect there was a burr in there somewhere causing the problem that I did not see originally. Since you are getting it anyways, maybe check and see how good/bad it is and then decide what you need. I use the 4 jaw frequently since I got pretty good at dialing it in quickly, so I have no plans to get a set through 3 jaw chuck.

I bought the ER-40 and 5c collet chucks from PM, both are set through and I have them dialed in to 0.0001” on the taper. I prefer using them over the jaw chucks since I can work close to them and not worry about knuckle busters. I got the inch set of ER collets, I should have gotten the metric set since there are gaps in usable ranges for some of the things I do, and the metric set has more collets. I got the inch set since I expected to use to mostly for raw stock, and some second operations, but since I do almost exclusively metric parts, I can’t hold some parts in it and have to switch to the 5c chuck. ER collets need the part to be long enough that it engages the majority of the collet, so you might need a 5c for second operations on short parts, but 5c collets have a very small clamping range that makes ER attractive, and with the PM collet set, your parts can’t be oversize at all, at least with my set. Which one, if any, are good for you will depend on the work you intend on doing.

 

[cathead]

To me a three jaw chuck is pretty useless so mine sits under the lathe collecting dust. Once you get used to
centering a round part with a four jaw chuck, it becomes routine. Maybe the reason I do this is because I have
two lathes in the shop and one has a home made 5C collet block installed pretty much all the time. It all depends
on what one machines so if you turn more odd shapes and do one-off repairs like I do, it might be worth some
consideration. If I did a bunch of pipe work, I might consider using the three jaw but that probably will not happen
any time soon. Another consideration is that just to change out the four jaw to a three jaw for one operation would
be pointless as it weighs in at about a hundred pounds.

 

[erikmannie]

My 6-jaw chuck is a Set-Tru. At least lately, it has seen the most use because I work on a lot of tubing and pipe.

When I first installed it, I very carefully used the Set-Tru adjustment to get TIR under .001”.

Since then, I use it as one would a 3J or 6J scroll chuck. That is, I have not yet revisited the Set-Tru adjustment screws. It merely functions as a scroll chuck with very low TIR.

I regularly take work out & then put it back in for further machining. To my pleasant surprise, I have had excellent repeatability.

One could imagine that you buy a scroll chuck & test the TIR when you install it. If that TIR was .001”, you would be very happy with that chuck.

Both of my 5C collet chucks are not Set-Tru, & I have to live with whatever TIR I get. Not the best situation for a 5C collet chuck.

If I am going to work on something that (1) will be removed & rechucked, and (2) calls for a very tight (e.g. .001”) tolerance, I use a 4-jaw.

 

[skcncx]

Thanks for every one's input!

For now I'm waiting on upgrading the chuck that comes with the PM-1236T, a 3 jaw economy chuck. Like @Ischgl99's input, it might be all I need for awhile. I have so many other things to buy as well.

When I'm ready or need higher precision on a 3 jaw the ultra precision from PM is a great value where price/accuracy meet. And at that point, it may be just get a 4 jaw for versatility. Though, I have yet to use a 4 jaw and have one for my atlas 618... for a few reasons, its never been worth it for one or two operations, I'm primarily doing round and hex stock, nothing square/odd shape to date and fear . I just gotta practice dialing one in. In the end I'd rather put $$ into a chuck that's likely the primary player most of the time. Or maybe the way the wind blows when I pick up my lathe in October if I see it on the shelf, could be impulse time.. though, I might reserve that for a small mill. Aren't we supposed to have both lathe and mill?

Sometimes the only way to know if something is worth it is to buy and try!