"Arch" wrote in message
...
"Speed Kills" is a general truism, but very often "Speed Helps". I don't
need to give examples of the value of speed, but what about spindle
speed in turning wood. I mean cutting and scraping _not sanding and
polishing.

I know that many good woodturners believe it best to work consistently
at speeds way below that necessary for safety and comfort. If it is
best, why is this preferable to turning as fast as the law allows
without being arrested for speeding? For me somehow, turning fast is
more enjoyable and things 'just seem to go better'. YMMV and it probably
does.

I can understand that the _way we turn plays a role in this. Ex: most of
us have to cut slower and deliberately as the tool nears the lower
velocity at the center of a large diameter blank. Since this is owing to
the lesser velocity at the center, it sort of makes my point, but again
YMMV.

_NOT considering sanding and polishing, what are some empiric, practical
and physical reasons for turning wood at a rpm below that which insures
comfort and safety for the turner and doesn't stress the equipment?
OTOH, why is turning at the highest possible rpm any better?


It's Newton. Remember that the energy at the tool is equal to half the mass
(or rotational inertia) times the velocity squared. As the energy required
to remove a shaving with a properly sharpened and presented edge is low,
evidence of which is provided when the shavings continue in the direction of
rotation - excess speed might well be considered as merely extra danger.
The shavings obey Newton's first law when properly removed by following the
vector course they posses by virtue of being in motion. When acted upon by
an outside force in a counterproductive direction, they follow the third law
by flying in the opposite direction. This puts a bunch of strain on the
tool, the operator, and the piece, because this force is in addition to that
required to overcome rotational inertia. Makes it tougher to clean up too,
because the shavings don't drop into the bag or stay on the gouge to be
dropped.
http://groups.msn.com/NovaOwners/geo...to&PhotoID=228
With my girth and age, I hate to bend over and shovel.

Further, when a piece is imperfectly balanced, as they almost all are at
some time, in spite of good preparation, the out-of-balance condition
creates asymmetrical force which increases by the radius of the center of
gravity (mass) from center of rotation. Said mass difference then varies
with the velocity squared. Double whammy, for those old enough to remember
Pansy Yokum.

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html Has some easily
understandable insights for turners. Without delving into inelastic versus
elastic collisions which cause the piece to distort, and distortion by
squirming caused by differences in the coefficient of friction by those who
think "riding" the bevel does nothing besides increase the heat, that's a
quick and dirty.

Removing the wood with the least required force is simply easier on your
elbow, the bearings, the rest, and the tool. When the amount of force
necessary to do the same job becomes greater due to blunting or edge
presentation, present properly and/or resharpen. Having all that potential
ready to ruin the piece or your day by speeding things up isn't worth the
price of the steel.