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Lathe Chucking Rule of Thumb


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Just wondering what the general rule of thumb on how large a part can be chucked in a given chuck size.  For instance, if you have a 10" chuck, can you chuck larger than the chuck diameter?  I know that there are ways to do so, but am wondering what the industry norm is.

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Just wondering what the general rule of thumb on how large a part can be chucked in a given chuck size.  For instance, if you have a 10" chuck, can you chuck larger than the chuck diameter?  I know that there are ways to do so, but am wondering what the industry norm is.

 

There is no industry "norm"

 

I would typically go by the swing available on the machine..

 

As you can flip jaws, size is confined by the swing

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Mill guy now for many years but I did a bunch of manual lathe stuff back a ways ( not saying how far back). So long as you don't hit the ways it's good to go. Might need some special jaws for holding or something and pay attention to your spindle speed. Did a lot of funky stuff. Here is one I did . Leveled it up. Chucked it in and clamped on some counter weights. Was for a 600 ton crane. Weighed I think around 600 lbs. Cleared the ways by thousandths lol.

 

 

post-12785-0-12852800-1476719264_thumb.jpg

 

post-12785-0-32022100-1476719273_thumb.jpg

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Nice crane part.  That's an odd shape, but still within your chuck diameter, so balancing is key as you did.  The swing would be your definite max diameter.  However, we've got a Doosan Lynx with a 6" chuck.  Doosan states that max turning diameter is 12.5".  Since there's not enough space put on a larger chuck, I would doubt that putting 12"dia on a 6" chuck is the smartest idea.  

 

On another lathe, we've got a 10" chuck.  I've chucked larger than the chuck diameter before, but what safety factor would you say is ok?  2, 4, 6in larger than chuck diameter?  

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Max swing of the machine max size part to put on the chuck. I have swung a 24" diameter part on 10" chuck. Machine had 26" of X diameter travel and with 2 face plates was able to machine the part. Work holding seems to be a lost art. I use to make crankshafts on a CNC Lathe. Really one of the 1st CNC Lathe jobs I programmed and setup from scratch. Was about 96 and and I use 2 Dead centers to hold the part. Once was on the center of one set of lobs and the other was on the other. Took me over 40 hours to program setup and prove out the part. I had never programmed CNC lathes before and had all my experience on CNC Mills before that point.

 

We use to run 42" diameter parts on 24" chuck on a 36" Swing Conventional lathe by removing the gap to turn the parts.

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Thanks for the replies.  I agree that workholding is a lost art.  It's hard to learn workholding creativity without going through the experience.  

 

How do you figure it's a "lost art"

 

It happens every day....and has gotten FAR more exotic in many corners....

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It depends a bit on the type of work you do.  We are not a job shop and have product lines that we manufacture.  Almost all parts are square or round, so workholding is always very straight forward.  

 

I figure it's a lost art both from our shops experience and from the people that I've interviewed.  We all know the job market is tight and hard to find employees.  Finding an experienced programmer/machinist where his experience actually means something is like a diamond in the rough.  That's my 2C and you can take it for what it's worth.

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