[TheForge] Re: Hammers

[Mike Spencer]

Andrew Vida <osan@netlabs.net> quoth:

	As for that, weight is one factor, but another it the diameter
	of the handle.  I have watched many smiths, particularly the
	less experienced ones, wielding hammers with these thick
	handles.  It took a while for me to figure that one out, too.
	I had a favorite hammer but I always got fatigued, but there
	was this large Stanley ball pein that I could work all day
	long without tiring.  I finally figured out that the Stanley
	had a very narrow handle.  When I whittled the other handle
	way down, I was in heaven with that hammer.

I would say just the same.  Bill Gichner once gave me a 2.5# cross
peen with a warped handle.  Didn't seem too wonderful and I blamed it
at first on the warp.  But after I slimmed the handle at the grip and
necked it down a bit near the head, it immediately became my favorite
hammer and still is, even after replacing the handle with a straight
one (and repeating the mods.)

There's another theoretical factor that I haven't explored but it's
one that may make a difference.  The "center of percussion" isn't
necessarily the same as the center of gravity.  It's similar to the
"sweet spot" on a baseball bat. [1] With a steel head and
a wooden handle, both centers fall somewhere within the head but a heavy
handle moves both back toward your hand.  If your hammer doesn't hit
the iron on (or on a line through) the center of percussion,
vibrations are set up that probably can fatigue your hand and arm even
if you don't notice them as you would the painful crack of a badly
hit baseball.

Ideally, the handle would have zero mass and the center of gravity and
center of percussion would (effectively) be in the center of the face.
I just googled this and the only mention wrt hand hammers seems to be a
post by (otherwise unidentified) Ron G on Keenjunk:

    I have made a lot of bad handles and a few good ones. I agree that a
    thin neck (light weight neck) is a very good thing, but not because of
    flex or shock absorbtion. The key IMO is to get the 'center of
    percussion' (AKA sweet spot) as close as possible to the point of
    impact, and thereby creating less shock. This means a minimum weight
    handle - especially in the neck. [2]

What Ron G calls "shock" is vibrations in the helve that have large
amplitude where your hand grips.  You can't eliminate vibrations but
you'd like to have your hand on a "node" where the amplitude of the
vibrations is (approximately) zero.

A trick I was shown (so long ago I forget by whom -- Bert Shaw maybe?)
is to make the handle with a gently tapered narrow neck between the
grip area and the head.  Then saw the handle from the head end
longways in both directions, (i.e. as if you were going to split it
lengthways into quarters) down to a couple of inches below the head.
Then mount the head and wedge with wood in both kerfs.  This makes a
nice limber, good-feeling helve but either I haven't got the knack
just right or the native ash available here isn't quite strong enough.
My experiments with this have broken too easily.  Hickory (which
doesn't grow here) or some other superior wood might be better.

- Mike


[1] See some nice animations as well as explanatory text at: [3]

       http://www.gmi.edu/~drussell/Demos/bats/bat1-bend.html

    It matters for some very light-weight hammers.  See:

      http://mmd.foxtail.com/Archives/Digests/199911/1999.11.27.09.html

[2] http://www.keenjunk.com/_junkyard/jp0012_2.htm


[3] It has been said that using footnotes in email is pretentious. :-)

-- 
Michael Spencer                  Nova Scotia, Canada 
                                 
mspencer@tallships.ca            
http://home.tallships.ca/mspencer/