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.

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.

I think that for those of us that turn a lot, we have our own comfortable speed ranges. In my own turning I find that faster is usually better. I have an 800 lb. lathe so vibration and lathe-walking isn't a problem. It is true that tools cut easier and better a higher speeds. However, safety issues are sometimes a deciding factor. Cracked wood, bark inclusions, etc.

If you think that having the piece fly off the lathe is because of too much speed, you're wrong. It's because the piece isn't securely fastened.

Wally

"Arch" wrote in message news: snipped-for-privacy@storefull-3176.bay.webtv.net...

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.

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.

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.

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.