On Jun 13, 11:26*pm, Ned Simmons wrote:

I agree with your conclusion, and I think for the same reasons. But I
don't agree that the "wrong" way applies the force on the moving jaw
in a different direction, i.e., pulls the jaw away from rather than
pushes it toward the frame.

To apply a torque to the nut there are two equal and opposite forces
(a couple, in statics jargon) applied to diagonally opposite corners
of the nut. (As you said, we can safely ignore the relatively small
force applied to the handle by your hand.) So depending on which way
you apply the wrench, the force on the adjustable jaw can be acting
either near the frame or near the tip of the jaw. In either case the
force applied to each jaw face is the same magnitude and direction,
and is resisted by the adjusting screw. What differs is the moment
produced by that force, which is trying to pry the jaw out of the
frame, and that moment increases as the point of application of the
force moves away from the frame.

Mark me down for pull with fixed jaw towards you.

--
Ned Simmons- Hide quoted text -

- Show quoted text -

Ned:

I'm glad you agree that pulling with the fixed jaw towards you makes
sense, because I now know that there are at least two of us doing it
the way that almost all others, in my experience, believe is wrong.

Since those forces are acting on diagonally opposite corners of the
nut, can't you look at the forces on each corner as two vectors - one
perpendicular to the face of the nut (and the face of the wrench), and
one at right angles to it? It's that second one that I'm seeing as
pushing the jaw towards or pulling it away from the frame of the
wrench.

It's been a long time since I took physics, though.

Maybe I should ask my younger son Matt, who has just finished his
second year in the physics PhD program at RPI. Here's a bet - if I do
ask him and he asks some of his physics and engineering buddies - my
bet is that there will be proponents in both camps.

John