Independent vs self-centering 4 jaw chucks: advice?

S

STEMtheMachining

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I'm looking at adding a 4 jaw chuck to my lathe, and this is a pretty simple question: if cost is not a factor, is there anything that a self centering chuck can grab that an independent 4 jaw chuck can't?

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I don't have a 4J self centering (scroll) chuck - guess I'll have to get one! Sooooo many toys to buy. Quick like a 3J, slightly less distortion on thinner pieces (i.e. plastic pipe), a little less deflection between the jaws compared to a 3J (a little less 3 lobe cogging on unsupported work). Of course the 6J does all those things even better, so very hard to justify a 4J scroll. I had one job on the CNC 4th axis that I had to snuggle in between the jaws to work two features 180° apart, so the spacing of the 3J didn't work. It was not a large piece run, but a 4J independent would have been a real pain to set for every part (and I don't have one setup for the 4th axis).

Maybe cool, but a pretty specialty item.
 
Don't they make 4-jaw scroll chucks with independent jaws too?
 
A 4J scroll is rarely used, one of the issues with 4J and 6J scrolls is that the stock needs to be symmetrical in diameter otherwise there may be an imbalance in the holding of a set of jaws. A 4J independent is more versatile, unless you need to do a lot of repeat work. The other downside is many 4J independent chucks have wide coarse jaws so may not work well for smaller stock. There are 4J combination chucks which have a scroll and separately adjustable jaws like and independent, the scroll repeats to about 0.001". They also have narrower jaws which will hold down to 0.2" on the Bison 8" combination. Grizzly is running a sale on the Bison chucks if you are looking, either 4J independent or combination.
 
No, there is nothing you can do with a 4-jaw scroll chuck that you cannot do with independent jaws. On the other hand there are many things you can do with independent jaws that you cannot do with a scroll chuck. I would not for a moment even consider a self-centering 4-jaw until long after getting an independent jaw. (I'm being kind, I really can't think of any reason at all to own a 4-jaw scroll chuck...)

GsT
 
@STEMtheMachining 4 jaw scroll chucks are only useful in very specific situations.

Frankly the extra use you'd get with the scroll is not worth the added expense and more importantly, weight. a 4J scroll with adjustable jaws weighs more than a 3J scroll chuck.

Spend the money on a high-quality independent 4J chuck you can trust. a loose fitting 4J chuck is more difficult to work with, and will discourage long term use.
 
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