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
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.
You are not thinking hard enough about the problem that is solved by impact
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
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.
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...
Joe Agro, Jr.
Automatic / Pneumatic Drills: http://www.AutoDrill.com
Multiple Spindle Drills: http://www.Multi-Drill.com
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.
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?
2008 10:22:27 -0400, Bill Smith, email@example.com 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.
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
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
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.
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