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Using a cutoff tool

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  • countrybj2006
    When using a cutoff tool, do you put the top edge at center? or just above? The other day when I was using the cutoff tool it caught and jumped causing the
    Message 1 of 2 , Feb 3, 2006
      When using a cutoff tool, do you put the top edge at center? or just
      above?
      The other day when I was using the cutoff tool it caught and jumped
      causing the piece I was cutting to break. I was using the back gears,
      so lathe was turning slow.
    • Jon Elson
      ... Cutoff work requires a very sturdy lathe and setup. The downward force on the toolpost, and the reaction to the high infeed force can lift the rear of the
      Message 2 of 2 , Feb 3, 2006
        countrybj2006 wrote:

        >When using a cutoff tool, do you put the top edge at center? or just
        >above?
        >The other day when I was using the cutoff tool it caught and jumped
        >causing the piece I was cutting to break. I was using the back gears,
        >so lathe was turning slow.
        >
        >
        Cutoff work requires a very sturdy lathe and setup. The downward force
        on the toolpost, and the reaction to the high infeed force can lift the
        rear of the carriage or otherwise deflect the lathe such that the tool tip
        goes below the workpiece center, or the workpiece climbs over the
        tool. If you chuck jaws are worn at the tips (VERY common) then you
        can't really grip the work right at the edge of the chuck jaws. You
        want the compound slide backed up such that the cutting edge is
        supported by the lower part of the compound and the cross slide.
        It may be necessary to tighten the compound gibs, or even the cross
        slide gibs, to keep things rigid.

        Grinding a slight groove in the top of the cutoff tool so that the
        chip folds inward on itself seems to help prevent the chip binding
        up on the sides of the cut. This groove should be radial from the
        workpiece, ie. running straight down the length of the cutoff tool.

        Lots of lube is needed to keep the chips flowing out of the groove.
        And, it may be that the backgear speed is too slow. Depending on
        the material, a higher speed may cut better. And, my experience
        is that parting-off large diameter pieces of aluminum may be a fool's
        errand, even on the most rigid of lathes, due to the extension of
        the tool bit required. It works great even for thick wall tubing, but
        if you have to go all the way to the center, it gets messy. I do all
        that work on the bandsaw, now.

        Jon
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