On Sun, 03 Oct 2004 19:36:22 -0700, Tim Douglass
wrote:
On Sun, 3 Oct 2004 18:57:09 -0500, "Todd Fatheree"
wrote:
However people confuse ejection for kickback,
where kickback is generally far more dangerous. Ejection occurs when the
workpiece is ejected straight back due to the friction force between the
workpiece and the saw blade. Per Kelly Mehler in _The Table Saw Book_,
"kickback is caused by the tendency of the rising teeth at the rear of the
blade to pick up the workpiece, catapulting it toward the operator at speeds
approaching 100 miles per hour." When this happens "the workpiece is
hurtled diagonally backward toward the operator." If you're standing to the
left of the blade, you're going to catch a kickback right in the gut.
I have never seen or heard of a saw actually kicking a piece in any
direction other than in line with the blade. Based on physics, I can
see a potential for the piece to perhaps move somewhat to one side or
the other depending on weight and contact with the fence, but for it
to be thrown so that it will hit an operator to the side seems
questionable.
I got whacked with a 2.5" x 2.5" x .75" piece of maple when
crosscutting, but I was stupidly using the fence as a spacer in
conjunction with my miter gauge. I did hit me when I was standing on
the left, but it was nowhere near as bad as kickback that shoots in
line with the blade. The gouge on the back of the wood was curved, so
it must have caught the fence somehow.
Consider: The piece gets caught on the teeth at the back of the saw
and the back edge of the piece rises, for all intents and purposes the
force acting on the wood is tangent to the circle of the saw blade.
The saw cannot exert any force to either side so I would assume that
the piece will rise from the table and the leading end will be kicked
upward and back in line with the blade. The piece will only travel
diagonally in the sense that it is moving up and back from the saw,
toward where an operator in-line with the blade will be standing.
I've had a few pieces of wood shoot across the shop, but only in line
with the blade.
Tim Douglass
http://www.DouglassClan.com