Thursday, March 01, 2018

Getting HAMMERED # 2 - Dynamics

Number two in a series :
Follows up from yesterday's post (looking at hammer shapes)

So - I had illustrated a number of the wide range of hammers, even in the same weight class, I keep here at the Wareham Forge.

I have a total of SEVEN hammers held in a basket, attached right at the anvil stub:
• my primary hammer (800 gm 'Engineer's')
• two rounding hammers (800 / 1000 gm 'Diamond')
• two wider cross peens (800 / 1000 gm 'Antique Farrier's')
• two heaver, sharp cross peens (1000 / 1500 gm 'Classic'
I have about another 10 more specialist hammers along the edge of the forge table. This includes various straight peen, ball peen, diagonal peen - with variations of weight / aggressiveness of peen. Plus a couple of replica Viking Age hammers. All those don't get used all that often, but are still close to hand.

What elements effect the dynamics of any given hammer?

click for roughly life size view

Here you see a comparison between a Swedish and 'Diamond' pattern. These two hammers that are the most different in the elements under discussion, plus my primary hammer (Engineer's). All three are 800 gms.

A - Distance of striking surface (face) from centre line
Swedish = 5.5 cm
Diamond = 4 cm
Engineer's = 6 cm

B - Mass distribution around centre line - head / core / peen - % (estimated)
Swedish ≠ 45 / 35 / 20
Diamond ≠ 30 / 40 / 30
Engineer's ≠ 40 / 40 / 20

Both of these elements, taken together, define the 'snap' against 'balance' as the hammer moves through the air.

A hammer with more of its mass forward the face, will tend to suddenly jump forward, as you swing it from vertical (starting position) to 90 degrees (striking the anvil).
This will accelerate the head, increasing the energy of the impact. *
However, this sudden 'snap' also puts increased strain on to the joints of the user, especially the elbow. (The 'French' pattern, with so much weight on the face side, is especially extreme in this effect.)

A hammer that has its mass centred on the handle will remain extremely balanced as it moves through the swing = better aim. This may reduce the possible impact energy of the stroke, but most importantly, it will greatly increase the ability to control not only the point of impact, but also the angle of the face when it strikes. The best example of this is the 'Hofi' pattern, which is perfectly balanced (1/3 to 1/3 to 1/3. With that hammer you can set an angle, then drop it - it will be in exactly the same angle (pitch and yaw) when it strikes the floor!)

Both are extremely critical in my opinion : "It don't matter how HARD you hit - if you MISS."

Both of these factors, balance and snap, will importantly effect individuals differently, largely based on physical size and strength.
Note here that these are NOT the same thing at all. Someone with a 'robust' bone frame, is not automatically strong - just as someone light of build is not necessarily 'weak'. That being said, the truth is that muscles can cushion bones and joints, but in turn can only prevent shock to a certain amount.

C - Handle length
Swedish = 35 cm
Diamond = 32.5 cm
Engineer's = 38.5 cm

The 'ideal' effective length for a hammer handle is based on the physical dimensions of the user. (This is simple ergonomics, the principle applies to swords, golf clubs, ... Almost any tool used in motion needs to be fitted to the individual body measurements.) *
The classic method to determine this 'ideal' is to place the butt end of the hammer on to the crook of your elbow, with your arm extended up, with fingers outstretched. The top edge if the head, hammer resting and extended along your forearm, should match the tips of those fingers.
(In my case, I have extremely long arms - thus the considerably longer than normal handle length. I find I just can not develop much impact force with the Diamond, although it is the same * mass * as my Engineer's. My partner Kelly, who is all of 4 foot 10 inches tall, uses one of the Diamonds as her primary hammer - at loves it.)

Next up - Fitting that Handle

* I may address the raw physics of hammer motion / energy in a further posting.

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February 15 - May 15, 2012 : Supported by a Crafts Projects - Creation and Development Grant

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