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Posted by Martin H. Eastburn on June 13, 2008, 11:09 pm
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I suppose you have to do the stress design on the entire part of the wrench.
This wasn't a obtw but from seasoned men I wish I had 1% of in me yelled to
stop...
Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/
John Martin wrote:
> wrote:
>> Take a wrench and hang it onto something.
>>
>> One way you are putting the pressure on the top jaw, the other way
>> puts it on the bottom jaw.
>>
>> You normally want it on the top one. The bottom jaw isn't as strong,
>> being that of a sliding jaw that moves side to side and in and out.
>> The latter can break if the main force is placed there.
>>
>> Martin
>>
>
> Martin:
>
> I think you're way off the mark with your mention of the "main force".
>
> As I see it, if you're pulling on a wrench with 100 pounds of force on
> the end of the handle, then the far jaw should have on it 100 more
> pounds of force than the near jaw. It's pretty much meaningless,
> though, because it is dwarfed by comparison to the force on the jaws
> coming from the nut's trying to wedge them open. That force is equal
> on both jaws.
>
> I wasn't trying to set you up with a trick question, though. I do
> expect that most people will say as you did: if you are pulling a
> wrench, the adjustable jaw should be toward you. I'm not sure that's
> right - here's why.
>
> If you're pulling on a wrench with the solid jaw away from you, the
> force is at the base of the solid jaw and the tip of the sliding jaw.
> The force on the sliding jaw is also to push it against the wrench
> frame.
>
> If you're puling on a wrench with the solid jaw toward you, the force
> is against the base of the sliding jaw, and is also to pull it away
> from the wrench frame.
>
> I'd rather have the force against the base of the sliding jaw, even
> though doing it "backwards" like that does try to pull the jaw out of
> the frame. But I'd like to hear what some others think.
>
> John Martin
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Posted by Ned Simmons on June 13, 2008, 11:26 pm
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On Thu, 12 Jun 2008 22:11:56 -0700 (PDT), John Martin
>wrote:
>> Take a wrench and hang it onto something.
>>
>> One way you are putting the pressure on the top jaw, the other way
>> puts it on the bottom jaw.
>>
>> You normally want it on the top one. The bottom jaw isn't as strong,
>> being that of a sliding jaw that moves side to side and in and out.
>> The latter can break if the main force is placed there.
>>
>> Martin
>>
>
>Martin:
>
>I think you're way off the mark with your mention of the "main force".
>
>As I see it, if you're pulling on a wrench with 100 pounds of force on
>the end of the handle, then the far jaw should have on it 100 more
>pounds of force than the near jaw. It's pretty much meaningless,
>though, because it is dwarfed by comparison to the force on the jaws
>coming from the nut's trying to wedge them open. That force is equal
>on both jaws.
>
>I wasn't trying to set you up with a trick question, though. I do
>expect that most people will say as you did: if you are pulling a
>wrench, the adjustable jaw should be toward you. I'm not sure that's
>right - here's why.
>
>If you're pulling on a wrench with the solid jaw away from you, the
>force is at the base of the solid jaw and the tip of the sliding jaw.
>The force on the sliding jaw is also to push it against the wrench
>frame.
>
>If you're puling on a wrench with the solid jaw toward you, the force
>is against the base of the sliding jaw, and is also to pull it away
>from the wrench frame.
>
>I'd rather have the force against the base of the sliding jaw, even
>though doing it "backwards" like that does try to pull the jaw out of
>the frame. But I'd like to hear what some others think.
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
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Posted by John Martin on June 14, 2008, 12:57 am
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> 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
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Posted by Leo Lichtman on June 14, 2008, 12:34 pm
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"John Martin" wrote: (clip)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? (clip)
^^^^^^^^^^^^^^^^^^^^
Yes, the forces can be resolved into two vectors, as you say, but if the
wrench is properly adjusted, the forces are essentially at right angles to
the jaw faces, so the second vector component is negligible. What makes the
difference is that one of the forces is close to the base of the jaw, and
the other is nearer the tip. Since the forces are equal, the one nearer the
tip creates more bending moment. You want this to be in the stronger jaw.
The movable jaw transmits its moment into the slot in the handle, which is
likely to be weaker than the stationary jaw. So you want it to receive less
moment. Therefore, turn the wrench so the force on the movable jaw is away
from, the tip.
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Posted by Mark Rand on June 14, 2008, 8:20 pm
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>
>The movable jaw transmits its moment into the slot in the handle, which is
>likely to be weaker than the stationary jaw. So you want it to receive less
>moment. Therefore, turn the wrench so the force on the movable jaw is away
>from, the tip.
>
Count that five for those that understand moments. I could never understand
how people could convince themselves that the other way was right.
Mark Rand
RTFM
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