3 jaw or 4 jaw chuck

[Sandyn]

I need to get a new chuck for my ML7 Lathe and favour a 4 jaw self centering chuck. I mainly turn round and square stock, never triangular or hex. I already have a 3 jaw self centering and 4 jaw independent, both are well past their best, but still usable. I'll probably get an HBM from RDG Tools, or Chronos.
Are there any disadvantage of the 4 jaw I haven't thought of?

 

[Daniel2]

I can imagine two limitations, rather than disadvantages, with this chuck.
First, is not being able to set the workpiece off centre, for certain operations.
Second is the inability to grip irregular shaped pieces, which includes pieces
of rectangular section.

 

[Rorschach]

I can imagine two limitations, rather than disadvantages, with this chuck.
First, is not being able to set the workpiece off centre, for certain operations.
Second is the inability to grip irregular shaped pieces, which includes pieces
of rectangular section.

He already has a 4jaw independent for those tasks.

I use a 4 jaw self centring chuck a lot, works great. The only thing you need to watch for is if you are using round stock that isn't perfectly round, a 3 jaw handles this much better and you would probably never even notice it wasn't round but in a 4 jaw you can run into some problems if you are not careful. Otherwise though, go for it, a 4 jaw SC gives you machining options that are almost impossible on a 3 jaw and for regular stock much faster than the 4 jaw IND.

 

[Daniel2]

He already has a 4jaw independent for those tasks.

I use a 4 jaw self centring chuck a lot, works great. The only thing you need to watch for is if you are using round stock that isn't perfectly round, a 3 jaw handles this much better and you would probably never even notice it wasn't round but in a 4 jaw you can run into some problems if you are not careful. Otherwise though, go for it, a 4 jaw SC gives you machining options that are almost impossible on a 3 jaw and for regular stock much faster than the 4 jaw IND.

I think a 4 jaw sc chuck is probably a very handy accessory, but, in addition to an
independant.
The OP's question was if there were any disadvantages, so I was trying to
imagine some.
It saves having to clock the work in, I suppose.

 

[TFrench]

I always find the more options you have, the better. Always having the right tool for the job saves a lot of struggle. If you turn a lot of square stock it makes perfect sense!

 

[Sandyn]

The only thing you need to watch for is if you are using round stock that isn't perfectly round, a 3 jaw handles this much better and you would probably never even notice it wasn't round but in a 4 jaw you can run into some problems if you are not careful.

That's just the kind of info I was looking for! I do turn a lot of rolled steel which is never really round. What you say suggests there are ways round the problem. Is it a case of rotating the bar until it grips better?

Thanks everyone for replies

 

[J-G]

Is it a case of rotating the bar until it grips better?

If your stock is out of round, rotating it in a four jaw SC chuck will have little effect since you will still be holding on only 3 of the jaws. It might be a different one that doesn't actually make contact.

It would be possible (though you may have to be very precise with your positioning) to hold on only two jaws of course. With a three jaw, the out of round issue goes away completely.

As @TFrench has said, having more options is certainly good and (for me) the availability of 'Soft' jaws is of paramount importance. I have 4 jaw Independent, 4 Jaw SC and 3 jaw SC chucks and all get used as needed but the majority of my work is done using soft jaws (mild steel or hardwood) on the SC chucks. My 4J SC is ostensibly a wood-turning chuck and therefore has carriers to which I can screw Steel, Brass, Alum, Beech, Oak (or any hardwood) 'Jaws' which I can machine to suit whatever work-piece is in use.

Using my CNC machine I can even accommodate 'off centre' or 'non-round' work.

The referenced chuck from RGD is unlikely to have either soft jaws or 'carriers' available.

 

[Phil Pascoe]

If your stock is out of round, rotating it in a four jaw SC chuck will have little effect since you will still be holding on only 3 of the jaws. It might be a different one that doesn't actually make contact. ...

It might, if you rotate only 45 degrees.

 

[J-G]

It might, if you rotate only 45 degrees.

It's a moot point Phil.

As I'm sure you'll appreciate (knowing my previous posts), I could go into great detail with drawings but I'll not bother

 

[Sandyn]

Thanks for all the replies and great information, I think a new 3 jaw would be more sensible to start with then get a new 4 Jaw independent if I find I still use the old one a lot.

 

[Daniel2]

 

[Rorschach]

That's just the kind of info I was looking for! I do turn a lot of rolled steel which is never really round. What you say suggests there are ways round the problem. Is it a case of rotating the bar until it grips better?

Thanks everyone for replies

Depends how out of round really. Usually turning it a little bit will help, a bit like the the old rotate your table if one of the legs wobble on uneven ground, you usually find a sweet spot that evens things up. A 3 jaw is definitely better for round stock that is a bit uneven but most round stock will be fine in the 4 jaw too. Really the 4jaw SC excels at holding square stock or self centring on odd stock be either gripping at 45deg or even just by taking out 2 jaws and using it as a 2 jaw chuck.

Like I said, I like mine, I use it an awful lot, way more than my 3 jaw chucks and almost as much as my collet chuck. It's a nice thing to have for any lathe user but I think a 3 jaw is still pretty essential for most people as well as the 4 jaw independent.

Collet chuck is really nice, you will want one of those too (I recommend ER40).

 

[Sandyn]

A 3 jaw is definitely better for round stock that is a bit uneven but most round stock will be fine in the 4 jaw too

Thanks. More good info, looks like it's time to get a coin out and make a decision!!

 

[Inspector]

If a 4 jaw is better than a 3 jaw then a 6 jaw has to be better than both of them.

Pete

 

[Fergie 307]

Surprised no one has mentioned the obvious problems with any SC chuck, namely that they don't hold a piece exactly on centre, there is always a degree of error. A real problem if you ever need to turn the work round and machine something concentric in the other end. With an independent you can do this, just down to how much trouble you are prepared to go to setting it accurately. And I would definitely go for a collet chuck. I have a 5c, use it all the time, and you can get square collets as well if you turn square stock a lot. Mine is only a cheap Chinese job, about £200. Pretty impressed with it though, accurate to about 0.001 inch which is plenty good enough for anything I do. Makes life very easy for anything that will fit in it.

 

[Rorschach]

Surprised no one has mentioned the obvious problems with any SC chuck, namely that they don't hold a piece exactly on centre, there is always a degree of error. A real problem if you ever need to turn the work round and machine something concentric in the other end. With an independent you can do this, just down to how much trouble you are prepared to go to setting it accurately. And I would definitely go for a collet chuck. I have a 5c, use it all the time, and you can get square collets as well if you turn square stock a lot. Mine is only a cheap Chinese job, about £200. Pretty impressed with it though, accurate to about 0.001 inch which is plenty good enough for anything I do. Makes life very easy for anything that will fit in it.

I would have thought that bit of knowledge was a given for any lathe user?

Collet chucks are definitely very useful, as I mentioned I have an ER40 which personally I think is the better choice for your average home DIY type lathe user for quite a few reasons.

 

[J-G]

...the obvious problems with any SC chuck, namely that they don't hold a piece exactly on centre, there is always a degree of error. A real problem if you ever need to turn the work round and machine something concentric in the other end.

That's precisely the reason that I use soft jaws and machine them concentric with the lathe centre-line each time I mount the chuck. This is even better than using a collet chuck (I do also have an ER32 Collet set).

'Clocking' work in an independent chuck is an art and, unless you have had many many years experience, is unlikely to be more efficient (time wise) than using soft jaws.

If I need absolute end-on-end concentricity I turn between centres.

 

[Rorschach]

That's precisely the reason that I use soft jaws and machine them concentric with the lathe centre-line each time I mount the chuck.

That assumes your scroll is accurate all the way through it's range of motion

 

[Daniel2]

.... and chasing that last elusive angstrom of precision.

 

[J-G]

.... and chasing that last elusive angstrom of precision.

For me that's a given

If you don't aim for it you'll never achieve it.