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Dan J -- The other guys have covered the potential problems with a 3-jaw chuck fairly well, but it does sound to me like your lathe bed may well be twisted. Assuming that your lathe is mounted on solid ground, one of the simplest and fastest ways to check a lathe for twisting is to use a precision level. As with most jobs, there are dozens of different ways to use a level to check for twisting . . . but the way I'd suggest involves running the carriage up as close to the headstock as it'll go and then setting the level (tool) on the top of the cross-slide or compound. Shim between the level and the lathe surface it's sitting on the bring the bubble to the center of the vial. Then, without moving anything else, crank the carriage down to the other end of the bed. The bubble should still be in the center of the vial; if it's not either the level moved on the carriage or the lathe bed is twisted. Run this test a couple times to be sure you get the same result, and then if necessary re-shim between the lathe bed and the bench at the tailstock end of the bed as needed to center the bubble in the vial. The millwright's standard level (tool) for setting up a lathe is called a "master precision level" and the vial is graduated so that roughly 0.0005 inch of tilt per foot is needed to change the bubble position in the vial by one division. The next step down is the "millwright's and mechanic's level", which is graduated so a tilt of 0.005 inch per foot moves the bubble one division. Either one of these tools should be adequate to set up a home shop lathe. Carpenter's levels don't usually have graduated vials -- and even a very good carpenter's level is not nearly as sensitive as a millwright's level -- but if a carpenter's level is the best level you can get you hands on, checking your lathe with a carpenter's level beats not checking it at all. John
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