Musing about spindle speed
 

"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?


Turn to Safety, Arch
Fortiter



http://community.webtv.net/almcc/MacsMusings

Musing about spindle speed
 

Arch wrote:
OTOH, why is turning at the highest possible rpm any better?

Two quick answers 'cus I have to go.

- high speed vibration is easier to overcome with out bodies.
- except for TaiChi masters, slow flowing movements are difficult to
achieve, and slow feed rates are needed at slow speeds.

--
Derek Andrews, woodturner

http://www.seafoamwoodturning.com
http://chipshop.blogspot.com - a blog for my customers
http://www.seafoamwoodturning.com/TheToolrest/ - a blog for woodturners

Musing about spindle speed
 

Because my lathe's motor is not very robust (That's what I get for
opting for the $200 H.F. cheapie), when I'm roughing larger bowls, it
stalls very easily at lower speeds. But, the lathe is dancing around
from the wood being out of round. I've noticed that a higher speed
gives a better centrifugal momentum (and faster cutting as a result),
but increases the risk of the blank flying off. This is especially
true because I usually initially rough between centers. Well, actually
the greater speed doesn't increase the chance of it flying off, but it
certainly affects at what force it flies off at!

Anywhoo - So far I've been hit in the belly/chest twice now by a 5-10
pound piece of wood flying out of control. From what I remember, it's
because I had the speed too high and I was standing in the wrong spot.
Me standing wherever doesn't affect the wood comming off, but it
certain affects how *I* end up. I suppose the cutting tool was to
"blame" as well (always the worker blaming his tools), since it caught
the piece good enough to throw the wood off center.

On body stance, there still is a chance that even if you've out of the
way, a piece could still hit you. I've had broken pieces bounce off
the wall(s) or other objects and hit me. In this case, usually the
force isn't good enough to cause any bodily damage. I'm positive
anyone reading this already knows all this.

My vote is lower speed for safety purposes. I'd rather take longer to
rough for the sake of being safe. I'm taking this in the context of
medium/large sized bowls. I'm not sure (yet) about spindle/smaller
works.

Musing about spindle speed
 

On Wed, 10 May 2006 09:21:07 -0400, (Arch) wrote:

_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?

For my part, I like turning fast- it gives me better results. Then I
sand at the lowest speed possible.

But here's a practical reason to slow the lathe down. Most of the
wood I turn is green, and I like to turn thin (3/16"-3/8") Depending
on the type of wood, spinning thin vessels too fast can cause them to
explode as they dry and crack- my guess is either that the air
whipping past the crack pulls the thing apart, or the tool tip gets
wedged in the new crack and breaks it up. Sounds like a small caliber
handgun going off, and can hurt a bit.

I know a lot of folks will say that turning fast is an indication of
poor technique, and that may be true- but I turn for fun, not to get a
good grade on it. What I find is that the peice stays a little more
true, and the chisel tends to fly over the low spots as the piece drys
and begins to deform. With a slow speed, my ham-fisted technique
tends to cause the chisel to follow the distortions in the bowl.

Musing about spindle speed
 

"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.

Musing about spindle speed
 

Brent wrote:
Because my lathe's motor is not very robust (That's what I get for
opting for the $200 H.F. cheapie), when I'm roughing larger bowls, it
stalls very easily at lower speeds. But, the lathe is dancing around
from the wood being out of round. I've noticed that a higher speed
gives a better centrifugal momentum (and faster cutting as a result),
but increases the risk of the blank flying off. This is especially
true because I usually initially rough between centers. Well, actually
the greater speed doesn't increase the chance of it flying off, but it
certainly affects at what force it flies off at!

Anywhoo - So far I've been hit in the belly/chest twice now by a 5-10
pound piece of wood flying out of control. From what I remember, it's
because I had the speed too high and I was standing in the wrong spot.
Me standing wherever doesn't affect the wood comming off, but it
certain affects how *I* end up. I suppose the cutting tool was to
"blame" as well (always the worker blaming his tools), since it caught
the piece good enough to throw the wood off center.

On body stance, there still is a chance that even if you've out of the
way, a piece could still hit you. I've had broken pieces bounce off
the wall(s) or other objects and hit me. In this case, usually the
force isn't good enough to cause any bodily damage. I'm positive
anyone reading this already knows all this.

My vote is lower speed for safety purposes. I'd rather take longer to
rough for the sake of being safe. I'm taking this in the context of
medium/large sized bowls. I'm not sure (yet) about spindle/smaller
works.

Musing about spindle speed
 

I generally rough at the slowest possible speed .I then shape at what I
feel is a medium speed.I almost always do a finishing cut at a medium
high speed. I was simply taught this procedure from an old and talented
turner and,it has always served me well.I have never had to use my
lathe above three quarters of the maximum speed.As for the higher speed
on the final cut,Maybe it is my imagination but...The chisel or scraper
doesn't seem to chatter as much and I feel that I am getting a cleaner
cut.