[TheForge] heavy hammers (Was Hammer Handles)

Fri Jan 9 08:58:15 EST 2009

A word of caution about heavy hammers.  I took a commission last summer that 
I designed using 1 1/4 square bar and 2"  thick-wall square tube.  Used a 5 
lb hammer for a week and I can still feel it in my elbows.  Learned the hard 
way that a heavy hammer does indeed require  a whole different technique, 
and especially moderation.  It has also been pointed out to me that the laws 
of physics actually sugggest hitting harder with a lighter hammer before 
going to a heavier hammer.

Movement of metal results from the amount of energy delivered in the blow. 
The kinetic energy of a moving object  (E) is a function of its mass (M) and 
the square of its velocity (V), in this proportion : E = 1/2 M x Vsquared. 
This means that you can double the energy delivered in a blow by doubling 
the hammer weight, but you quadruple the enrgy by doubling the speed of the 
blow.

But if you double the weight,  you double the amount of force not only 
required to lift it but also the force required to bring it down at the same 
speed, unless you are just letting that light hammer fall on its own, which 
I bet you are not.  Remember gravity accelerates all objects at the same 
rate, regardless of mass, so you have to supply the rest of the force 
required to move that heavier hammer at the same speed as the lighter one..

  If on the other hand you use the same hammer, and double the speed of the 
blow (by doubling the force of the downstroke) you quadruple  the energy of 
the blow.  Light hammer plus same force in the upstroke, double the force in 
the down stroke equals four times the energy in the blow.  HEAVY hammer, 
plus twice the force in the upstroke and twice the force in the downstroke 
equals only twice the energy in the blow.  And believe me, its the upstroke 
that kills the elbow.  That's why they call it TENNIS elbow, not boxing 
elbow.

Note that if you are doubling hammer weight but laying off on the 
downstroke, you are getting less than double the energy into the blow, and 
may not even be getting as much energy into it as with the lighter hammer. 
This is also why some power hammers can move more metal than others of the 
same or even much heavier weights: speed of the downstroke.

Once you have achieved all the VELOCITY in the blow that you can control, 
physics tells us that then and only then should you go to a heavier hammer. 
And when you do, lift it with the shoulder muscles (as in the description of 
Rick SMith's heavy hammer technique) rather than the  bicep and flexing 
elbow. Turn the hammer vertical with the wrist and rebound, lock the elbow 
and lift from the shoulder. you will find that the blow is delivered with 
wrist and shoulder action, very little movement in the elbow and very little 
bursitis resulting.  One smith I work with reflects this:  forearms like 
Popeye, shoulders like Schwarzenegger, and biceps like me.

BTW, FWIW, Mike's description of the old guy with the fish knives is exacly 
the classic hammer technique I was taught years ago -- and hardly ever 
use -- for all hammering at a BGOP demo years ago.

----- Original Message ----- 
From: "Mike Spencer" <mspencer at tallships.ca>
To: <theforge at mailman.qth.net>
Sent: Friday, January 09, 2009 2:19 AM
Subject: [TheForge] Re: Wooden Hammer Handles

>
>> At a CBA demo years ago, Rick Smith drew out a billet of fancy
>> pattern welded steel in one or 2 heats using a big hammer ( 6-7#s?
>> or more)....It looked like he didn't begin lifting the handle at the
>> moment of impact like i usually do, but rather, waited while the
>> rebound rotated the handle to a nearly vertical orientation. So when
>> he began his lift the hammer head was oddly close to his chest,
>> balanced atop the handle.
>
> Yeah, something like that was what I meant when I said, "...with a 5#
> hammer unless I use it very differently from the way I swing my
> favored 2-1/2# hammer."  I've found that slower and it uses very
> different muscles overall.
>
>> He moved a very impressive mass of steel...
>
> Maybe I should practice more with the 5-pounder instead of trying to
> avoid it where possible.
>
>> Wish we could run differing styles of hammering through the same
>> imaging process.
>
> Yeah.  Me too.  My annual gig at MIT evaporated after '95 and it was a
> significant hassle, even then, to arrange and coordinate the use of
> the cam and dedicated computer that Kodak had donated to the Edgerton
> lab.  Since then, I haven't thought of any way to prevail upon Kodak
> or its competitors to provide me with the hardware.  (Suggestions
> welcome. :-) It would be a whole lot of fun to do repeated runs with
> different smiths, hammers, anvil heights and so on.  Even to shoot the
> parts of running mechanical power hammers to tune them.
>
> The Edgerton lab also had a hammer with a built-in accelerometer and
> data cable.  When I heard about that I was keen to forge with it but
> was informed that it was more on the order of a tack hammer or light
> mallet and didn't come even close to being usable for forging iron.
> One of the students had it set up in a vise and was firing paint balls
> at it for some kind of undergrad physics experiment.
>
>
> - Mike
>
> -- 
> Michael Spencer                  Nova Scotia, Canada       .~.
>                                                           /V\
> mspencer at tallships.ca                                     /( )\
> http://home.tallships.ca/mspencer/                        ^^-^^
>
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