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Lathe chucks

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rleete:
I have a Homier 7x12 "Speedway" lathe.  One of the chinese clones.  It came with a 3" self-centering 3 jaw chuck. 

Recently I obtained a small piece of DOM tubing in 3" ID.  Just barely too big for my 3" chuck to hold.  Pity, as it would make excellent rims for flywheels.  So, I started looking at getting another chuck.

LMS and others sell a 4" and a 5" version.  The price difference is minimal ($95 vs. $105).  Both include the adapter at that price.  Is there any big disadvantage to getting the larger one? 

bogstandard:
Roger,

First off, couldn't you use the normal jaws for holding the tube internally?


I personally wouldn't go too large, just because it fits, doesn't mean it is right. I could, in theory, put a 17" chuck on mine, but I think the lathe would disintegrate when I turned it on.

A couple of reasons, the first being the larger the chuck, the more mass on startup to get it turning. I know nothing about your lathe, but if it uses those electriconical circuit board thingies, you might just overload it and burn it out. The same goes for actually turning, the larger the item held and turned, the more loading on the motor and board.

The second is actually the mechanical bits of your lathe. These machines are usually made down to a price, and everything on them is designed to do the job and not much more, bearings, gears etc.

So looking at it, go for a larger chuck, but don't push it by going too far.

With the few bucks saved by going for the smaller of the two, look to see if you can put it towards buying a set of soft jaws for the chuck you buy, that will really help improve your tolerances greatly.

I hope this helps

John

foozer:

--- Quote from: rleete on July 26, 2009, 09:35:02 PM ---I have a Homier 7x12 "Speedway" lathe.  One of the chinese clones.  It came with a 3" self-centering 3 jaw chuck.  


--- End quote ---

Like the man said, bigger not always better. I have a 6 inch faceplate 1 inch thick AL for my AA109. No way, no how do I crank the speed up, just to much rotating mass. Fitted a 3 inch Taig soft jaw chuck and its pure heaven. Has low mass so can crank it up over 3000rpm with little worry. Can make the jaw pieces for those times when the part is just a tad too big. They virtually eliminate any chuck runout, need to face off flywheels, wonderful tool for that.

Check out Bogs Making a Flywheel post, the pics explain better than I. Cant take hard cuts with em, but then the little lathes argue that point anyway. Was money well spent.

Robert

Stilldrillin:
I now have a 4" chuck on my Churchill 7 x 20.

There is a very noticeable difference in rotating mass, overcoming the starting, & stopping inertia.

I mostly use the lower gear ratio (to 1,100rpm), but always build up the revs over a couple of seconds, or so.......

David D

Darren:
Hi Roger, there is another issue I believe with the larger 5" chuck.

You can't open the jaws out fully as they will hit the bed, so no real gain over a 4" size.

The extra mass would be my biggest concern though as has already been mentioned.

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