Chuck size question

I'm looking to buy a 4 jaw chuck for my lathe. I have a 10" lathe (Atlas 10X36) and an 8" 3 jaw chuck already
I'm Looking to add a 4 jaw and i'm wondering if there are advantages to using a bigger chuck over a small one other than the Obvious of being able to chuck up bigger work. and the Obvious Disadvantage in price.
Assuming i dont need to put anything over 6" in the chuck are there other advantages to having a bigger chuck over a little one?
And anyone selling a 4 jaw that fits a 1 1/2" x 8 TPI threaded spindle?
Thanks all
Brent
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Brent Philion wrote:

A 9" lathe uses a 6" 4-jaw and a 5" 3-jaw. Presumably you could go as large as 7" on a 4-jaw. Have to be careful of projecting jaws hitting you or the ways or the apron. Other drawback to larger chucks is the weight, although a 7" chuck won't strain you too bad.
Be careful buying used 4-jaws, if the jaws are bell-mouthed you'll have a lot of trouble. I suggest the PC brand from ipstool.com, they seem like some crappy import but I have one of their 3-jaws, use it a lot, *much* better than my original chuck that came (in 1949) with my lathe. They are reasonably priced, too.
GWE
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Grant Erwin wrote:

My current 3 jaw is 7 1/2 inches and it appears to have over an inch of clearance over the cross slide on it
My face plate is 8 1/2 and it clears fine too
Can the bigger chuck cause additional wear? Or have smoother cuts due to the chucked work having more inertia and be deflected less by the cutter? Or something else entirely that i havent considered
I'm a newbie on the machining side and would like to continue using this lathe until its a working antique (instead of just being almost double my age)
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    [ ... ]

    [ ... ]

    What happens when the jaws are extended for grasping the maximum size object possible with the non-reversed jaws? Will the extension of the jaws hit the cross slide then?

    But a face plate does not have extending jaws.
FWIW, on my 12x24" Clausing, I'm running a 6-1/4" 3-jaw chuck with two-piece jaws, so I can either reverse the hardened top jaws or mount and bore soft jaws for special tasks.
    As far as a 4-jaw, I'm running a 10" Bernard Pratt, but I am very careful about checking clearance if the jaws extend beyond the rim of the chuck (and really they should not do so by very much at all, as such loading stresses the ways in which the jaws run.
    Note that the length (thickness) of a 3-jaw chuck is typically greater than that of a 4-jaw chuck (the need for room for the pinion and scroll plate), and even more so with a Set-Tru feature added. This increases the leverage of the cuts to increase the chance of chatter.
    My rule of thumb is that a 3-jaw chuck should be on the order of half the size of the lathe's maximum swing. A 4-jaw can be significantly larger, as can a faceplate, which is significantly thinner than the 4-jaw even.

    It can speed wear on plain bearings. Of course, so can the weight of a large workpiece. I would not expect much effect with either ball bearings or roller bearings.
    It can also increase the chance of bending the spindle in case of a crash. The larger the diameter of the spindle, the less likely this is to happen.

    It can, indeed. And, it can smooth out angular vibrations during turning as well, with the inertia of the chuck helping tomaintain a constant spindle speed.

    Good luckk with that.
    Enjoy,         DoN.
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I've got an essentially new 8" Bison 4-jaw chuck with 1-1/2-8 backplate that is surplus now that I no longer have my 12x36 Craftsman lathe. That's probably too big for you, but email me if you are interseted in it.
Mike
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