On 08/30/2011 12:49 AM, Dave wrote:
On Mon, 29 Aug 2011 19:44:41 -0800, Kevin
wrote:

I never developed much of an interest in turning, but I've always
wondered how a burl like that is turned. Specifically, how do you
prevent it from cracking and breaking up completely while turning with
all the existing cracks and voids? I'm assuming, maybe incorrectly,
that there must be some type of violent vibration when a cutting tool
crosses a void or a crack.

There is a bit of chatter when crossing voids, but in general it isn't
so bad as one might suspect. It depends on several things such as the
speed the bowl is spiinning at, how sharp your tools are, what type of
cut you're making and how deep of a cut.

Even at a slow speed like 500-600 rpm the about of time the tool crosses
the void is so minimal that the tool doesn't really have a chance to
deviate from the path it's on so when it encounters the far side of the
void it hasn't significantly changed the geometry of the cut.

Dealing with cracks is an issue at times. I've had wood fly apart on me
when the rotational stresses were too much. A full face shield is a
must. In this case, by design, I left the walls pretty thick so there
was plenty of sound wood to work with so it wasn't a major concern.

....Kevin
--
Kevin Miller
Juneau, Alaska
http://www.alaska.net/~atftb
"In the history of the world, no one has ever washed a rented car."
- Lawrence Summers