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Posted to rec.crafts.woodturning
George
 
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Default Vibration Hollowing A Bowl


"Barry N. Turner" wrote in message
. ..
Another friend of mine suggested that I take the bowl walls to final
thickness incrementally, say an inch at a time, rather than making one
sweeping cut from rim to bottom. I think that may work. I just didn't
expect to have vibration when the walls were well over an inch thick.

It's not the lathe. All four (4) feet are solidly on the floor. I don't
think it was the speed either, but it could have been. I tend to turn
slower than most people I know. The blank appears sound. I have some
doubts about the 1/4" bowl gouge too. I have one, but have never used it.


On a rim that thick, at relatively slow speed, I'd inspect the mounting.
Applies to wobble both free and with a load. You wouldn't be the first guy,
especially on green wood, to have squeezed too hard and crushed some fibers
so the chuck's no longer firm. Especially if you're holding wet sapwood.
Shake the piece. If it moves, re mount.

If it's not moving on its own, but only under load, it's the presentation of
the edge or the pressure on the bevel. With a 1/4" flute, you don't have to
be cutting too deep to bury the upper, non-cutting part of the profile, and
that will cause you to rip and slide over end and side grain. The pickup
fuzz should be obvious on green wood if this is the case.

Last, you could be riding that bevel. That will still give you a relatively
fuzz-free cut, but you'll get out-of-round really rapidly due to the
difference between end and face grain. If the gouge wants to move in and
out, that's what you've got. Sometimes you can even see compressed lighter
areas against a wet background where you rubbed the heel of the bevel too
hard trying to make a quick curve.

Changing speed is often suggested, but it's really the same as those folks
who say if you drive your car faster down a washboard gravel road you won't
feel it as bad. You'll still beat the crap out of your car, of course, and
increase the impact force with the square of the velocity, not to mention
the loss of control as your shocks are no longer able to get the wheels back
to the road. Same on the lathe. I turn slow, too. No problem, as long as
you sharpen and present properly. You can carve with only the gouge in
motion, after all.

A 1/4" gouge is a great tool where the curvature is fast, or the access
narrow. Use it where you have to, though mine has almost no grind at the
ears, making it more suitable for the above uses.

One last shot in the dark, though this one should have been obvious at the
get-go. I once cut a blank from wood that had been on its side for a while,
ending up with all the water on one side of the blank. That was a grin and
bear it. Not to mention, I had another blank to cut just like it,
afterward....