On Sun, 13 Jul 2003 15:19:31 GMT, (Gary Coffman)
wrote:

On 10 Jul 2003 16:32:36 -0700, jim rozen wrote:
You need to be more specific about the 'critical speed'
problem.

What it means is, unless the entire shaft that protrudes
is *securely* supported along its ENTIRE length, the
machine operator will be confronted with a piece of
one inch diamter bar stock that has bent at a 90
degree angle where it emerges from the far side
of the headstock, and is WHIPPING around in
a huge circle at about 1000 rpm.

Ask me how I know. :-(

Gary

Sometime ago, I got stupid and in a hurry, and did just that, with a
piece of 303 5/16", about 3 feet long. Stuck it out the collet in the
Hardinge, leaving about 18" sticking out.

I would have SWORN the speed was set to about 100 rpm ( I was going to
part off several pieces)..but in fact it was set to 3000 rpm.

It got really exciting there for a minute or two, and while it didnt
harm the lathe besides removing some paint, it did cost me a nice
plastic trash can, an oiler, a nifty gouge in the wall, and a couple
years off my life.

I went into a shop a few years ago, where this had been done with a
piece of 1. 25" leadloy. The machinist had put the 5' stubb on stands
but didnt secure the stands very well. It actually moved that 16"
lathe about 4 feet before they managed to get the main power turned
off. Screwed up the floor, the walls, several workbenches and the
machinists chance to advance in that company......

Gunner

"What do you call someone in possesion of all the facts? Paranoid.-William Burroughs