I am not an engineer, but the number can't be less than 600 pounds.  
And that is a pretty good force for a 9 year old to develop. :>)

On Oct 5, 2005, at 7:57 AM, Blake Ashley wrote:

>  Maybe an engineer can tell us how much force
> is developed by a half-inch screw being turned by say 50 pounds at the
> end of a 12 inch lever? I'm sure it isn't an issue if the vise is used
> properly.   But it just kinda soured me on the design.
>
Jim Thompson, the old millrat in Riverside, CA.

------------------------------------------------------------------------