PICTURE -- Big vs. small impact wrench

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Your statement indicating that you've never looked at the design, explains why you don't understand the actions involved, and why the rest of your theories about the tools' actions are incorrect.
The rotational direction of the striking parts is not reversed, doesn't change direction (unless the user changes the direction of the output to reverse the direction of rotation of the fastener).
The striking parts work with other parts to deliver glancing blows to the driven parts (output shaft).
BTW, the impacting action doesn't start until the fastener exhibits some rotational resistance/opposition to the tool's output (the fastener being installed becomes seated, a self-locking fastener, rusted or damaged threads, or a seated fastener needs impacting force to loosen it). However, mechanics that frequently assemble threaded parts cross-threaded, will experience the impacting action more often.
The practice of starting the fastener for the first couple of turns with just finger power generally eliminates the possibility of cross-threading the fastener.
Normally, the tool acts like a rotational driver unless a high(er) driving force needs to be applied.
Typically, some torque can be felt by the user that holds an air-operated impact wrench not attached to a fastener, and gooses the trigger to wide-open repeatedly, just to hear the tool's exaust noise. This torque is caused by the tool's air motor rotor jumping from zero/low speed to full speed, and the counter force of compressed air acting between the tool housing and the air motor's moving parts.
WB ......... metalworking projects www.kwagmire.com/metal_proj.html


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You are not thinking hard enough about the problem that is solved by impact wrenches.
The only net torque that must get transfered to the operator is the torque required to make the nut and socket and rotate in free space - aka when not attached to anything. This is because as the nut comes off, the only thing that actually moves, is the nut and the internal parts of the wrench, and therefor the only torque that must be transfered to the operator is the torque required to turn the nut a few rotations if it were floating in weightless in space - which is basically something even a 50 lb kid could support.
The very large amounts of torque applied to break the nut free is applied, and then removed - so the net change is zero. In a perfect impact driver, if the nut didn't move, the operator would feel no torque at all.
It works because it applies a large amount of torque in a short time - which causes some part of the wrench to start moving, but then a smaller torque is applied in the opposite direction for a longer period of time, causing the moving parts to come to a stop - with no need to transfer any net motion or torque to the operator if the nut didn't move. And when the nut does move, the only torque transfered to the operator is the torque to overcome the angular momentum of the nut.
Still, life is not perfect, and I'll bet that big ass wrench could knock a very big guy on his butt at times.
--
Curt Welch http://CurtWelch.Com /
snipped-for-privacy@kcwc.com http://NewsReader.Com /
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wrote:

More likely if the big guy was off balance when he tried to pick the tool up. ;~)
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Ah, the patch.....
I remember many times when roughnecks would ask to borrow "those little wrenches" (anything smaller than 2").
-Zz
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Google search Bob Sapp and re-evaluate. :)
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Joe Agro, Jr.
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Sorry. If you can't post a cite to back up your argument, it has to be a weak argument.
Steve
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Steve, IIRC Joe makes a living working with this kind of stuff.
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Hmm... Define "Makes a living" <grin>
It was more of a joke than a serious post although Bob Sapp is probably one of the scariest human beings on the face of the earth when it comes to raw strength and size. If there is a human who can conquer the larger tools without beinbg tossed around like a play thing, it's him. Of course, he probably doesn't have a minute of tool training in him so who knows...
Regards, Joe Agro, Jr. (800) 871-5022 01.908.542.0244 Automatic / Pneumatic Drills: http://www.AutoDrill.com Multiple Spindle Drills: http://www.Multi-Drill.com
V8013-R
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I'm no pipsqueak, but this guy looks like he could frighten a 5" diameter bolt loose!!!
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Yet a real pipsqueak could get the big bolt off there using the proper technique and tool. Sometimes big guys are plain vanilla dangerous.
Steve
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SteveB wrote:

Did you happen to see the "Dirty Jobs" episode in which one of the jobs was changing a tire on a heavy recovery vehicle? The motor pool sergeant weighed about half what the tire did (and she was kinda cute too) and had no trouble handling one. On the other hand, Mike Rowe, trying to do it by brute force and awfulness instead of by using the tools designed for the job, managed to drop one on a cameraman, who fortunately managed to avoid injury.
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--John
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wrote:

I was a Teamster for 37 years. One of the favorite sayings was, "Give a lazy man a job, and they will find the quickest easiest way every time."
Steve
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J. Clarke, snipped-for-privacy@cox.net wrote:

I didn't see the show, but I have to weigh in here. A heavy recovery vehicle doesn't have tires, it has tracks. ;-)
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wrote:

And the Heavy Recovery Vehicle (M88A2) has a 1" hydraulic impact in its arsenal. The M88A1 was considered a Medium Recovery Vehicle. The M578 is a Light recovery vehicle and it has tracks too.
The 10-Ton HEMTT (Wrecker) could be considered a Heavy "Wheeled Vehicle" Recovery Vehicle and it does have large tires. The 900Series 5-Ton Wrecker would be a Medium/Light Wheeled Recovery Vehicle..
Only the M88, M88A1 and M88A2 have the 1" hydraulic impact wrench (which runs off the Little Joe APU). There is a lot of feedback to the operator with one of those. Been there, done that.
Anything else no-one wanted to know?
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Smitty
Somerset, PA
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Bill Smith wrote:

And that is IIRC the vehicle in question. The cameraman was _not_ a happy camper after the wheel and tire landed on him.

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2008 10:22:27 -0400, Bill Smith, snipped-for-privacy@wpia.net wrote:

Yup, M88's were exactly what I was thinking of. A2 version was well after my time. According to wikipedia A1 was also "Heavy" with only the original M88 being "Medium." Maybe wikipedia needs a "fix" on that point?
I was on the Service side of S&R and S&E platoons, so I rarely went out on recoveries.

Yup, those too. Even had the "opportunity" to help change some of those tires. My faded memories seem to include 3 guys to get those HEMMT tires off the rims. I'd have sure liked to see that episode of Dirty Jobs.

There's a couple of wikipedia pages that refreshed some memories. http://en.wikipedia.org/wiki/M88_Recovery_Vehicle http://en.wikipedia.org/wiki/HEMTT
Heh, ever seen an M88A1 try to drive on glare ice over cobblestones on a slope? Downright funny (though potentially quite dangerous).
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--
Smitty
Somerset, PA
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I think anyone who REALLY knows and understands tools will say, beef don't matter. And little guys can get just as much done or more by using their heads, leverage, and by using the tool properly.
It is common for a power tool to eat the lunch of even the beefiest operator when that operator doesn't use the tool properly, or tries to use muscle over technique. Many amputees will verify this fact of life.
There is no glory in someone being so burly as to use power tools in an unsafe and unintentioned way over the skinniest guy using it right and getting the job done and going home with all his fingers. If I had to work with either, give me the skinny safe operator rather than the beefcake showoff.
Steve
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That is correct. When I was operating the 1" impact drives I was 22 years old and a heafty 125 lbs. dripping wet with sweat. I will say that the first time I looked at it I was very intemidated. One of the mechanics told me that if I can simply lift it I would have no problem after that. After grabing and holding on for dear life I was shocked at how little effort was actually required.
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Yer right. My comments were just a general statement about power tools, and not any one in particular. But even if it's a simple pry bar, you have to admit someone who knows how to use it RIGHT will use less effort than some big Bubba who just uses force.
Steve
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