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Peter N
10-28-2006, 01:36 PM
Loosely related to a previous thread about fixtures, I’ve been thinking about the various approaches to clamping round stock, and whether 3-point or 4-point clamping is more appropriate depending on direction of force, or where the resistance to force is required.

Obviously both methods utilise vee’s – giving 2 pressure points – and a flat opposing plate will give a 3rd pressure point, or an opposing vee will give 4 pressure points.

Machine vices with jaws for round stock usually have a single vee and opposing flat, but bench vices for pipes etc. have double vee’s. The machine vice is usually clamping against an x-y type force while a pipe vice is clamping against rotational forces.

I started doing some force/vector calculations but gave up as it was no fun and many years since I was any good at these :D , so I thought I would throw this open to the board for any opinions as to which is best for which situation.

So, any thoughts on this (theoretical) question gentlemen?

Peter

John Stevenson
10-28-2006, 03:13 PM
No................................................ ...................................



.

Peter N
10-28-2006, 04:25 PM
No................................................ ...................................
.

I said Gentlemen :D :D

I take that a plain 'no' was just too short?

Ed Tipton
10-28-2006, 06:03 PM
Peter... that is an interesting question. I do not pretend to be smart enough to solve it mathematically, but I do have a thought about it. This is no doubt an over-simplification of the problem and of course in any given situation.... At first glance, the tendency is to say the four point clamping would be superior, but consider a three legged table vs a four legged table. On a level surface, with equal weight applied to both tables, both are steady. But, given a situation where the floor or pressure is uneven, the four legged table will tend to "rock" whereas the three legged table will remain steady as long as all three legs are bearing weight. While some may say that this is an apples vs oranges scenario, I think it may have some merit. Obviously the forces generated when making chips is very different, but as the cutter moves with respect to the workpiece, the forces applied to the workpiece and the associated clamping would change considerably in both direction and magnitude. Just a thought.:o