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chuck a chuck onto a lathe?

Gordon Heaton

Stainless
Joined
Feb 19, 2007
Location
St. George, Utah
People do it. If you're chucking a 6" in a 9" you'll be turning the jaws around so grip length will be pretty short, and overall stickout will be long. For light cuts it should work.
 

partsproduction

Titanium
Joined
Aug 22, 2011
Location
Oregon coast
First though, perhaps a mental exercise of imagination would help, imagine a chuck, or any heavy object, dancing at high speeds around the shop floor. I think about that every time I chuck large objects, especially out of balance parts, and the farther a part or a chuck sticks out of the chuck the more potential danger the setup has.
The affect this concept has on me is to make me take the time to make sure it's safe, and that speeds are appropriately lower before starting the spindle.
Of course that's SOP.
 

wood2steel

Aluminum
Joined
May 17, 2013
Location
georgia
Taiwan L,
I prefer to have the small chuck mounted to an arbor shaft instead. I have a 4" and a 6" 4 jaw that have long enough arbors to fit deep in my Lodge and shipley 12" chucks. Nobody's going anywhere here. Arbor and chuck's are machined together so runout issues are very minimal. Use them often for very small 1 or 2 part runs. Just run them at lower rpm speeds when possible.
Johnny
 

4GSR

Diamond
Joined
Jan 25, 2005
Location
Victoria, Texas, USA
Place I worked at years ago had a nitwit chuck up a 15" 3-jaw chuck up in a 19" power chuck in a Daewood CNC lathe. Needless to say, got up to running speed and facing tool engaged the work piece. The 15" chuck came out of the power chuck and when the dust settled there wasn't one piece of sheet metal that wasn't dented up and destroyed. So be careful how you do it! Ken
 

wood2steel

Aluminum
Joined
May 17, 2013
Location
georgia
Ken, You've got that right! Holding a hobby lathe chuck in a real man's machine is perfectly OK. Putting a 300 lb chuck in a machine with a 310 lb chuck is INSANE! There ARE limits!!!
 

dcsipo

Titanium
Joined
Oct 13, 2014
Location
Baldwin, MD/USA
Is it ok, or safe if say a lathe has a 9 inch 3 jaw chuck, but I chuck another smaller lathe chuck (say a 6" 4 jaw) onto the 3 jaw chuck?

Is this done, or if it's even safe to do?

I read somewhere that it's not allowed...

Why are you doing this? If to hold something that is smaller than the smallest diameter the big chuck can grip, then use a smaller chuck, like a 3" or even a 2" chuck, whatever is the largest your 9" can grab without using outside jaws. Using the outside jaws on a larger chuck will create a real knuckle buster. It is also a more common practice to hold a small 3 jaw in a larger 4 jaw. Once you dial in the OD of the small chuck the 3 jaw chuck will repeat reasonably well. In the reverse setup, you have to indicate every part. In case you do not have a 4 jaw mountable for your lathe, well maybe it is time to get one :)
 

john.k

Diamond
Joined
Dec 21, 2012
Location
Brisbane Qld Australia
Ive done it many times........supposed to be dangerous in certain circumstances.......and there are pics on PM of a chuck in chuck that let go at 3krpms,and went through a CNC machine enclosure ,thru a workshp partition and thru a block wall...........this of course is extreme......and would never happen to me!
 

Marty Feldman

Titanium
Joined
Feb 21, 2005
Location
Owl's Head, Maine
You ask "Is it ok, or safe..." There is too much risk here for the answer to be a simple yes or no. It could be safe if you've got sound machine sense, but the fact that you are asking suggests that you may not have the experience to do this safely. Exactly what are the details of your job that prompts this? Why not invest in proper workholding gear?

-Marty-
 

thermite

Diamond
Is it ok, or safe if say a lathe has a 9 inch 3 jaw chuck, but I chuck another smaller lathe chuck (say a 6" 4 jaw) onto the 3 jaw chuck?

Is this done, or if it's even safe to do?

I read somewhere that it's not allowed...

Bad idea with that combo, especially.

- To the good, a 3-J scroll typically has HALF the grip of a 4-J independent.
So it is less likely to damage the aft body of the 4-J than the other way 'round - 4J gripping a 3-J.

(Lest we forget that a chuck body is NOT "solid".... there are limits to how much grip force may be safely applied before something is damaged or flexes and impairs grip..)

- To the bad, by the same metric, half the grip means it is twice as likely to come OUT under stress!

If you have a 6" "flat back" 4-J, or one with the wrong mount that can be removed.. wiser to spend the usually modest price of a backplate.

Machine it on the lathe so as to give the 6" its OWN mount.

Swap as needed.
 
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Nmbmxer

Hot Rolled
Joined
Jun 22, 2008
Location
VA
I prefer to use an adapter bolted to the face of the larger chuck. I used a 6” adjust tru bolted to the face of a power chuck in my hobby shop for years. If I could justify setting.up soft jaws I would, if the part was small (hard to make small soft jaws imho) it went in the 3 jaw.

Currently for my manual lathe I have adapter plates for the face of my 12” 4jaw for the same 6” adjust tru, 6” 4 jaw (grips small od’s) and a 5c chuck. Quite handy and it beats changing out 12” A2-6 chucks. You also have to watch the speed rating of the larger chuck but I’d you remove the jaws and bolt to it you don’t.
 

Big B

Diamond
Joined
Jun 26, 2009
Location
Michigan, USA
First though, perhaps a mental exercise of imagination would help, imagine a chuck, or any heavy object, dancing at high speeds around the shop floor. I think about that every time I chuck large objects, especially out of balance parts, and the farther a part or a chuck sticks out of the chuck the more potential danger the setup has.
The affect this concept has on me is to make me take the time to make sure it's safe, and that speeds are appropriately lower before starting the spindle.
Of course that's SOP.

Why would a small chuck be any more prone to coming out of a larger chuck than any other steel object of it's size? And as long as the smaller chuck has something tightly chucked in it there shouldn't be any problem with any thing coming loose there either.
 

Turbowerks

Cast Iron
Joined
Nov 9, 2018
Location
Windom
Why would a small chuck be any more prone to coming out of a larger chuck than any other steel object of it's size? And as long as the smaller chuck has something tightly chucked in it there shouldn't be any problem with any thing coming loose there either.

I agree with this statement but because of circumstances involved on such a setup a little common sense needs to come into play. I’ve done some sketchy setups with multiple chucks to get things done. Would i put the rookie on it? Probably not but if you need to, you need to


When I find it I don’t need it
When I need it I can’t find it!
 

CalG

Diamond
Joined
Dec 30, 2008
Location
Vt USA
I hope it's OK. I do it frequently.

I've got a six inch four jaw on a 5C Stub arbor. and another Outside jaws only three jaw on a 1 inch stub.

Sometimes I'll mount either of them into the 12 inch chuck on the bigger lathe. If the four jaw is holding the little three jaw. It's sort of a poor man's adjust-tru. ;-)
 








 
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