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New Metalworking Lathe... need help...


bjhines

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i've just got a Lathe myself (borrowed from a mate who is moving for a few months) and i was trying to find some info on how to centre the 3 jaw chuck a little better as it seems to not be centering very well.

 

i've read through the links posted and dont think the mods in

http://warhammer.mcc.virginia.edu/ty/7x10/vault/Lathes/7x10-7x12-Projects/SetTruBackplate/

are really something i wanna do with a borrowed Lathe

 

 

any tips would be great

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Generaly, 3 jaws simply do not run perfectly concentric, just the nature of the beast. Some can get pretty close, granted, but if you REALLY need to be precise, then a 4 jaw is what you need. Although a 4 jaw requires more skill/know how to set up a piece properly, it is the best way to run the piece perfectly true. That is an interesting link, but I would still go for a 4 jaw myself.. I don't believe that his 3 jaw (modified as it is) is going to be MORE acurate than a 4 jaw.. it just takes a lot of effort to get the 4 jaws running prefect (read; skill and patience!).

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How to center a 3 jaw: If the chuck itself is not acurate, clamp something in it to secure the jaws, and cut them true with either a boring bar (inside jaws) or tool bit (outside jaws). Generally, my chinese 3" 3 jaw clamps work perfectly, with no radial runout. I also have a chinese bandsaw that couldn't cut straight if my life depended on it, so if I chuck up something that I've cut on the bandsaw and measure runout an inch or so away from the chuck, its all over the place. Just get a dial indicator and small mallet and tap tap tap until you can measure runout in 2 places on your piece of stock and come up with 0. I through a hub on my 7x12 the other night to try to make it fit in a cobra rotor, and measured runout on the hub face as well as the radial runout. It took all of 2 minutes to get everything to 0. 4 jaw chucks are a pain in the ass. Maybe I'm just slow, but I usually spend at least 10 minutes or so trying to get something straight in a 4 jaw. I only use it for cutting odd shaped stock or offset holes. The 3 jaw gets used for everything else.

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