Lathe size vs 4-jaw chuck capacity

[Dunc]

This 10 inch lathe, http://busybeetools.ca/cgi-bin/picture10?NTITEM=B2227L
has a 5 inch 4-jaw chuck recommended (optional purchase).

This 9 inch lathe, http://busybeetools.ca/cgi-bin/picture10?NTITEM=CT039 has a 7.5 inch 4-jaw chuck included.

Why does the smaller capacity lathe have a larger chuck?
What is/are the (a) reason(s) for this?

Is there a formula/rule of thumb to relate lathe size to chuck size ( 3- and 4-jaw)?

Any other thoughts?

[JCHannum]

The 7-1/2" chuck will not prove very useful on a 9" lathe. Once the jaws are slightly opened, they will foul on the bed. I suspect the information on the data sheet is a misprint.

Chuck size is typically about half the swing for a three jaw and the next size larger for a four jaw. Chuck size for a 9" swing lathe would be a 4" three jaw and 5" four jaw. Add an inch for a 10" swing lathe.

[airsmith282]

you can use upto a 6 inch chuck on the 10x18 but your asking for trouble on lager stock..
the 9inch well pretty much the same why they do it who knows

id stick with the 5 inch 4 jaw for sure on the 10x18 anyway

i thnk 10 inch is really a myth i mounted a 9 inch band saw wheel once on my b2227L and it had just enough clearence under neath so a 10 inch would fit but there would be no room for wobble if the peice was dead centre in the chuck,there would be less then a MM of clearence

[Ian B]

JC,

You're right about the jaws on an "oversized" 4 jaw fouling the bed - this happens on my little ML10 with a 5" 4 jaw. It always annoyed me.

Then I realised that I could hold the same size work that I could with a smaller chuck, but the jaws at full extent were much better supported than they'd have been with the smaller chuck.

Arguably, a smaller (ie. lighter) chuck would also have slightly thinner steps on the jaws, allowing a slightly greater holding capacity - a few mm maybe.

An oversized 4 jaw looks odd on a lathe. However, apart from this, and assuming you're smart enough to turn the spindle over by hand before running on power, is a bigger chuck a problem?

Ian

[knudsen]

Just cuz it fits don't make it right. Ref: Rogue's Gallery thread.

[airsmith282]

what i think i would worry about on a larger then reccomended chuck would be how the bearings would react your talking more weight in the larger then reccomended chuck as well this might cause some bearing issues i would think,also would the spindel shaft not being built to spec for a larger the reccommended chuck would it suffer any problems ???

[kvom]

Reversible jaws allow a larger chuck to be used vs. one with non-reversible jaws.

[airsmith282]

Reversible jaws allow a larger chuck to be used vs. one with non-reversible jaws.

explain this in a bit more detail, forgive the ignorece but last time i checked reversable jaws allow the holding of a larger diamter peice this has nothing to do with holding a larger chuck.

[knudsen]

I read the post as meaning, for example, in a 4" chuck, you could flip the jaws around and hold a 3" bar (very short slice to be practical) without the jaws sticking out as they would if not reversed.

[Black_Moons]

yea the reversed jaw position lets the steps hold large stock without the jaws being extended so far, and also grip very large pipe from the inside with lots of the jaw.
the normal position lets you hold small stock very securely and get it further out from the chuck/jaws to help keep the jaws outta the way of your toolpost/etc, as well as hold verious sizes of pipe from the inside.

4 jaw independant chucks almost allways have reverseable jaws afaik
3 jaw chucks require 2 sets of jaws, one normal, one reversed, or two part jaws.
while two part jaws require possabley a little more effort to reverse, the possability of making deticated soft jaws outta aluminum/mild steel often outweighs that disadvanged in the long run.

I would'nt worry too much about the bearings, even on a small lathe the bearings should be good for a lot of weight due to having to surive cutting forces and the odd minor crash.

[S_J_H]

The 7.5" chuck that comes with some of the import 9x20's is a faceplate type or wood working chuck.
They look just like this one-

http://grizzly.com/products/4-Jaw-Chuck/G1082

They are lightweight chucks with a crude jaw system. There is a nut on the back side of each of the 4 chuck jaws not seen in the above link which also needs to be tightened once the chuck is adjusted.
But they work "kind of Ok" on the 9x lathes once you get used to using them.

If you look at the bearing load ratings on most lathes, you'll see the bearings will handle anything you could hang off them... well within reason.

Steve

[pipeclay]

I often use my 8" chuck on my 9" lathe ,when turning 127 tooth gear blanks,it comes down to correct holding method for the job at hand.