Lathe Chuck Sizes

[Jammer Six]

Given a small lathe, (9x20, in this case) what is the biggest three jaw chuck you would use?

Is it different for a four jaw?

It seems to me that collet chucks are all smaller, they're all in the less-than-one-inch range.

How do you decide what size chuck to use for a given job?

[140mower]

A typical size for a 9 or 10" South Bend would be a 5" 3 jaw and 6" 4 jaw and an 8" face plate. I would think that the same would apply.

[The Metal Butcher]

5-6"

Sometimes. I size 3 jaws around typical work diameter. I size 4 jaws to the best size for the maximum swing of the lathe. Say for a 14" lathe, a 10" with the jaws sticking out 2" will hold the biggest part the lathe can swing. A 4-5" 3 jaw is typically about right for that machine and a 6" 4 jaw will be nearly perfect for all but the biggest jobs.

I typically use a 12" 4 jaw because I trust it not to throw parts on my 18.5". It is heavy so I typically leave it on. I try to have the jaws inside the chuck body for most jobs, when practical, so there is a kinda-sorta rule of thumb.

I also have a 12" 3 jaw that fits the envelope well on that machine. On dad's 14" machine, we typically use a 9" 3 jaw and a 10" 4 jaw. On the 14" machine at work we use a 10" 3 and 4 jaw. On my 20" class Daewoo, I have a 16" 3 jaw that is about right, though I would prefer a 12" 6 jaw for daily work and a 16-18" 4 jaw. On dad's 10" Rockwell he has a 6" 6 jaw which is perfect and a light duty 8" 4 jaw which is also perfect. I made a backplate for a 7.5" 3 jaw and it is decidedly too big. It is much less stiff due to the extra stickout.

Today I used an 8" chuck on my 18.5" lathe because it was the only one that fit inside the part and gripped it properly. Sometimes you need various chucks.

Collets are for small stuff, yes.

Hopefully that gives you some feel for what is "right". It comes down to preference and what is safe for the job.

[JRouche]

Given a small lathe, (9x20, in this case) what is the biggest three jaw chuck you would use?

Is it different for a four jaw?

It seems to me that collet chucks are all smaller, they're all in the less-than-one-inch range.

How do you decide what size chuck to use for a given job?

Great questions I think.

I have a nine or ten inch lathe. I like the six inch size chuck, . Four or three. JR

[Doozer]

When I was younger, I had a 10" Atlas (sucky) lathe
and I bought a brand new Bison 8" three jaw from Enco.
It was really too big, because you had to be careful to
prevent the jaws from hitting the carriage wings when
they were extended way out. But it really was not a problem.
I was happy with my choice, because even though technically
too large, it allowed me to chuck much larger work. I ended up
building a project that required turning some 6" dia plates for
wheel flanges and brake rotor flanges. The 8" chuck I bought
was perfect for that. I don't think a 6" chuck would have been
able to grab the plates I was machining.
If you have a 9" lathe, 6" would be max. I have seen 7" chucks
but they are rare. I think Vertex makes one. But 7" is the outer
limit. Don't forget, when chucks get larger, they get thicker, and
that means more stick out distance from the spindle bearings.
That means less rigid. So if you can afford it, it is handy to have
a few different size chucks for your lathe. Collet chucks too.

--Doozer

[Georgineer]

... Don't forget, when chucks get larger, they get thicker, and
that means more stick out distance from the spindle bearings.
That means less rigid. So if you can afford it, it is handy to have
a few different size chucks for your lathe. Collet chucks too.

--Doozer

What he said! (My emphasis.)

In my experience, three-jaw chucks tend to stick out further than four-jaws, because the body has to accommodate the scroll mechanism.

George

[old mart]

The Smart & Brown model A at the museum is a 9 x 20 and I have 100mm, 125mm, 5" , 6" 160mm and a 6 3/4". The optimum sizes IMO are 5" or 125mm threejaw scroll and 160mm four jaw independent. A lightweight 6" four jaw independent is at least 1 1/4" shorter than a 160mm standard type and may be a better choice.

[J Tiers]

Decent rule.... 3 jaw 1/2 to 2/3 the size of the swing as a general max. A 4 jaw can be a bit larger. Yes, you need to consider some stickout of the jaws in certain cases, but that is not required if the chuck is bigger, as you need not extend the jaws for that same piece that you need to work on.... use your head and consider the limits..