Discussion in 'Newbie' started by Paul A. Lewis, Apr 17, 2009.
Hello forum, my first post and my question is. Do you get less catches at a higher speed and RPM?
Catches don't diminish with speed, rather with tool control. You've got three good helpers to give you control - the rest, your arm and the work itself.
The rest should be kept in close, as close as you can manage, and if that means stopping and adjusting closer every minute, so be it. Idea is to limit the downward distance the tool can move in a "catch."
With the rest in close, and your "good" hand out near the end of your tool handle, you can make large moves at the handle which make small adjustments at the cutting edge. You also have, if you keep the tool handle within a 20 degree angle to horizontal, a great force multiplier to counter downward thrust as well. This multiplier (leverage) diminishes as the tool handle falls. At 90 degrees your arm and the work are on an equal footing or less, since you have to support the weight of the tool as well. Makes your rest pretty well worthless as a support as well, so you're in double jeopardy.
The work also helps with tool control. You can keep the tool at an effective angle more easily if you let the bevel of the tool maintain contact with the wood where you've been as you move toward your destination. Lots of grinds have variable angles, which can make things unstable and cause the tool to roll and catch, since they have a gap behind the bevel along your direction of advance. So stay in the sweet spot and don't make pitch or roll adjustments that might get you in trouble. Yaw the tool into (and out of) the work.
The wood will teach you how it wishes to be cut. When it's willing, the shavings slide down or across the tool with almost no pressure on your hand. If you increase depth of cut you increase the pressure downward against the rest, which doesn't care, and against your arm, which may tire, but so long as you're on both rest and bevel, you won't catch.
Thank you Michael, that was very helpful and informative.
Michael if I could add a comment to your excellent narrative. Tool control is improved greatly by using your body not just your arm. If you visualize where you want the tool to go, that is from the start to the finish of the cut, than plant you feet and position you body to move through the cut not just your arm. Than, with your hand near the end of the tool handle press the handle to your hip. The mass of you body is less likely to be effected by the tool than your arm. To illustrate the point, Stand six or eight inches further away from the lathe bed than usual and plant your feet. Now use just your arms and shoulders to make a long sweeping cut say on the outside of a bowl. I think you will notice a sever loss of control. I think David Ellsworth calls this "Dancing with the Lathe"
Almost as important as an orderly approach to the cut, is an orderly withdrawal. It doesn't take much inattention to produce a spectacular catch. Easier to do than to describe.
Absolutely. I look like I should put on a yarmulke and tallit at my lathe. Might as well be at the Western Wall the way my body moves in and out with the weight shifts.
Small muscles can't maintain the tool attitude properly. They retreat at a bump and advance reflexively. Often they advance with less-than perfect alignment. One reason why I don't use an underhand grip with my "off" hand. First, it's the clumsy one, second, it's a one-to-one movement in that close, rather than a twenty to one. On a pull cut I have to use that clumsy hand to move the tool, but I prefer to lock and lean.
Use your ears instead of just your muscles. Especially the small ones. Equilibrioception over proprioception for heavy work. Keep the rest and the bevel on your side, of course.