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View Full Version : How does one measure a chuck?



oddball racing
01-12-2009, 09:02 PM
I keep seeing various chuck sizes. How are they measured? Is a 8" chuck 8" in DIA, or does it hold an 8" piece of stock?

Boucher
01-12-2009, 09:06 PM
It is 8 inches in diameter.

Teenage_Machinist
01-13-2009, 12:20 AM
Approximately 8 inch diameter, that is. Many are metric.

A 4-jaw can often hold things bigger than itself.

dp
01-13-2009, 02:42 AM
Approximately 8 inch diameter, that is. Many are metric.

A 4-jaw can often hold things bigger than itself.

I've never seen a lath chuck that cannot hold an object larger than itself. A three or 4-jaw chuck can be expanded to internally chuck a cylinder larger in diameter than the chuck, for example, though it is probably not common to do so. When chucking the internal diameter of a work that has been bored the only limit on the outer diameter is that of the space over the ways - and hopefully your cross slide and compound are out of the way.

Teenage_Machinist
01-13-2009, 09:13 PM
Umm, my 4 inch 4 jaw holds 4 inch-slightly more and could take a bit more. Also LMS rates practical max as 5 inchs which seems too high.

dp
01-13-2009, 09:36 PM
Umm, my 4 inch 4 jaw holds 4 inch-slightly more and could take a bit more. Also LMS rates practical max as 5 inchs which seems too high.

Is that in compression or extension? Here's a picture of a 4-jaw (scroll down a bit) with the jaws fully extended - imagine now a large diameter pipe (larger than the chuck) fitted over the outside of the extremities of the jaws. The other end of the pipe might be fixed in a cat head or steady rest.

http://mini-lathe.org.uk/mini_lathe_chuck.shtml

A 4-jaw chuck can chuck a 9" brake rotor by placing the jaws inside the hub and expanding the jaws. You'll definitely need head room to do that.