Shock absorbing hammer design

[Bob_Nor]

I earn my money in the office and do quite a bit of different hand work in my spare time, but I'm not really perfectly suited to the hard physical work I tackle. We heat our house partly with wood and in the past my wrists and hands were the body parts that limited my work volume when splitting wood. I then bought a Fiskars plastic handled axe without expecting much and was really astonished to realize, that it had much less rebound in the handle and made splitting wood much easier for me.

Fiskars x25 axe

The handle is made from fibre reinforced polyamide and is hollow. It won't be possible to produce such a handle for a hammer and plastic handles would't survive long in blacksmithing anyway.

A couple of years ago I was astonished to hear that Hofi fits the heads of his hammers with Sikaflex elastic glue to reduce rebound and immediately like the idea. Has anybody looked closer at the different possiblities to design a shock absorbing hammer?

Different design ideas come to my mind: Sikaflex-mounting, rubber bushes, hollow handles, shock absorbing handle cover. For me shock reduction would be most interesting in a blacksmith hammer, a smaller sledge and a framing hammer.

I would like to make some shock absorbing hammers and would like to discuss the design. What is you experience, what are your ideas?

 

Bob

[gote]

I never feel any shock or rebound in the hammer handle.  I do not think that there should be any if the head hits square on. I get shock in my left hand if I hold the stock in the wrong way and hit it when too cold. If I have to adjust something cold I put a heavy winter glove on my left hand.

Splitting wood is adifferent thing but I usually I get no rebound there either.

I do not hold the ax or hammer very hard and I use the whole handle. I do not use the edge of the head as a fuller - I use the edge of the anvil or the pein. I keep thye anvil at the height recommended by Glenn, Frosty and others, i.e so that a natural swing hits squarely.

 

[ThomasPowers]

For hammering we teach our students to NOT use a death grip on the handle; to have a very loose grip and so shock is not transmitted into the hand-wrist-arm.

From old european smiths I have been told that they should be able to stand by you and pluck the hammer out of your hand with no resistance anywhere in the swing.  I prefer to have a terminal bulb on the handle to provide a "stop" so I don't accidentally throw it in use...

[Frank Turley]

If purchasing a handle, you'll often get 2nd growth Hickory, which is OK. However, the entire haft is often oversized. Imagine yourself holding the wrong end of a baseball bat. I exaggerate.

I rasp or shave and/or sand my new hafts so they are quite slender in the neck area, and the handle portion is reduced to fit my hand. The slender neck allows some whip and shock absorbency. I definitely want to remove the shellac or varnish coating that is often covering a new haft. I give my hafts a coating of half linseed oil, half turpentine.

[Mark Ling]

this is just my preferences:

no varnish on my handles; I prefer linseed oil.

I cant stand fiberglass or any synthetic handles. I once bought one from lowes and ended up cutting of the plastic handle, drilling out the eye and putting in a wooden handle on.

also I prefer wedges. they have worked for people all around the world for a very long time, so why not keep it that way? and I really injoy putting new handles on hammers and wedging them.

I have never had any problems with shock; it may just be the way your gripping it.

                                                                                            Littleblacksmith

[ThomasPowers]

I've been trying to remember the difference in the way I swing an axe and the way I swing a hammer and realize that hewing, felling and splitting all had variations on how I hold and swing the axe and they differ quite a lot with how I hammer steel.

 

However it really comes down to "What works for YOU!" and "What YOU like!"  sometimes we can advise of possible problems some people have run into doing it that way; but that is more of a suggestion than a hard fast law.

[Charles R. Stevens]

I'm with Frank, resizing your hammer handle helps a lot, as do properly dressing your hammer head, you do not want dead flat (my rounding hammers were, and they jerkeked in the hand if you didn't hit the stock flat) I have also seen the handle slotted near the head. 

Honestly the biggest is to reshape the handle

[Bob_Nor]

You are right, I forgot the probably most important part: The lighter the grip, the less shock is transmitted. And the shape of the face also influences the generation of rebound, when the workpiece is not hit straight.

Here are som pics to illustrate the topic:

My axes

It is clear, that the wood handles are not shaped very well. They don't expand to the end, they get slightly thinner. The big 3 kg splitting hammer is a standard type that is sold in Germany in masses. The handles are also quite fat. Maybe the splitting hammer handle is made to withstand inexpert use.

Some hammer handles I made

from left to right:

1. Ball peen hammer with round face, handle expands, but could be a bit thicker for the weight of the hammer

2. Diagonal peen hammer, good grip behind the head and at the end of the handle. The finish is a bit too smooth. The wood should offer quite good damping, it is soft and flexible.

3. Small ball peen with round face, good shape but a bit too thin

4. Soft ball peen, handle could have a bit more shape

 

My sledge hammers

5 kg with long handle, german standard type, ash handle could probably be a bit thinner and could have a much better shape

3 kg with fat short handle, german standard type, in this condition completely useless, much more rebound than 5kg version. Ash handle needs to be a lot thinner and must have a much better shape

 

So probably the starting point always has to be the shape and texture of the handle. What I would like to find out is, what a shock dampening connection between handle and head could offer in addition. Has sanybody had the opportunity to compare a Sikaflex-Hofi-hammer with a comparable shape of hammer with standard wedging of the head?

 

Bob

[Charles R. Stevens]

Ok, handle thickness is dependent on your hands, but I find US made "blacksmith" handles to be to thick, but better than hand sledge handles. 

 

[Charles R. Stevens]

I know a lot of pictures, but it gives a point a reference. The first hammer is a 4# hand sledge with the handle shaved down, it is still a bit thick but not as bad as it was. The second hammer is an odd Asian hammer, the handle is just about right. And the last is a reference to my hand, tho I am 6'2" I don't have meat hooks. 

i don't have an issue with standard sledges used two handed, much of that is technic, as I was about 8 when I learned to swing an 8# sledge. Talk about letting the hammer do the work, lol. Re work your hand hammers untile you are confortable, strait for most of their length, as this allows you to "choke up" for finer control and use the full handle for heavy blows. Chose a handle length that reaches the inside of your elbow when the head is filed in your hand. 

Ovoid the death grip, I occasionally throw the hammer (let it get away) cold adjusting shoes. I my self use a modified sword grip, to say my pinky grips tighter, with each finger griping progresively less, but this is flexible as my grip tightens and loosens threw my swing.  

[Charles R. Stevens]

Their is a technich to to lifting the hammer as well, when making full swings, tilt the hammer so the handle points up, then lift the hammer over your head, this reduces the leverage of the head on your arm. Now as you swing you guide the head, exelerating threw the first 2/3 to 3/4 of the swing, bringing the handle fully vertical at the last of the swing. A similar technic with the sledge and splitting mall, now I admit to standing tall, even to raising my heals to get every bit of hight to start the swing, using even my back and legs, starting with bent knees and ending with them, but I am known to choke up on a 14# sledge and one hand it. 

A note to sledge handles, for smithing you want it short, cup the head in your hand and the handle should reach your arm pit, will your splitting mall and regular sledge will reach from cuped hand to we get of chest. 

[Charles R. Stevens]

Anvil hight is an issue as well, setting your anvil at rist hight for light forging with a hand hammer and little use of top tools, fist high for heavier hand forging, light sledge and top tools and first knuckle for heavy sledge work (remember to bend your knees). Same with your splitting anvil, cut your stump so the top of your average peice of fire wood is from rist to first knuckle. Use your legs and back and relaxe at the end of the swing. 

[Crazy Ivan]

I've heard some farriers wrap their handle in the eyes with a bicycle inner tube to mount it more securely and supposedly to absorb some shock. I can't say that it works for that or not but it might be worth a try. Good advise already above. Especially about the loose grip. 

[gote]

Fiskars are known for using ergonomic design. I think that the ax is good because the edge has the right shape and the right angle to the handle and the handle has the right profile. I doubt that any flexing has anything to do with it. Some tools are just badly designed. Some are designed to do a different job than that which they are put to do. When you get a tool designed by a real pro for the job you are doing, that makes all the difference; be it hammer, sledge, ax, spade or whatever.

[rockstar.esq]

So far nobodys mentioned that the length of the handle influences the shock transmitted.  Every standing frequency will have nodes which are points where the vibration is maximized, as well as anti-nodes where the vibration is effectively zero.

If the handle were a completely uniform shape from hammer head to the end, there would be a spot somewhere along the line that has less vibration.  If the handle was sufficiently long, you'd find that there are similar low vibration spots at regular intervals.

I have a couple of hammers with handles that are pretty uniform along their length.  Based on the stains in the wood, I can see that I'm gripping in two spots depending on whether I'm choking up for control, or falling back for a heavier blow.

I strongly suspect that I end up at those points because it's more comfortable. 

Please note that most of that goes out the window when you've got a handle that's got a skinny neck, and a coke bottle swell going on.  Thicker masses will resonate differently than thinner masses.  Perfectly designed handles will put your hand on the anti-node while providing sufficient leverage, and control of the tools mass. 

Also, it's worth mentioning that putting your thumb on the back of the handle seems to magnify the shock transmission into your arm.

[ThomasPowers]

Got that backwards; nodes are places where it's zero and anti nodes are places where it's max; the link covers that.

This also a reason that swords are not just big knives.  if you don't have a node at the grip you've made a sword that will jump out of your hand in use.

[Bob_Nor]

The standing frequency of the handle will be lowered if the handle is made thinner. A very stiff handle will have maximus and minimums within the lenght of the hands grip. In this case the position of the hand wouldn't matter very much. My 3kg sledge has a short, fat handle and is extremely uncomfortable to use. Compared to the 5 kg sledge the shape and texture are nearly the same, so the "death grip" argument doesn't count here.

Probably the handle of the 3 kg sledge would have to be thinned first to make it tuneable and then the shape and length have to be adjusted to the least vibration at the grip point. It might even be possible to show the standing frequency on the handle by finely spreading some powder on it and look where it is shaken off.

I sure that one feels the best point on the handle with your hands, but I don't really like to hit with a hammer holding it more than a hand width from the end of the handle. So for me it would not be easy to test for the best point.

Compared to the position of the maximum amplitude the overall level of acceleration of the hand by the rebound is more important from my point of view. My 3kg sledge has a very harsh transmission, probably due to the short fat handle. I don't use it much, so optimizing it is a low priority project.

For me it's very interesting to see how much details have to be right to get a hammer that is a joy to use. The hammer - the most basic tool, a better club. Not really !!!

[rockstar.esq]

Thomas, thanks for the correction.  I typed it right the first time, then corrected myself.

 

[ThomasPowers]

NP I double checked to make sure I was remembering it right before I posted!

[navasky]

There's the double s driving hammer but I have no idea how effective it is.

[Bob_Nor]

Using O-rings as damping material is a good idea. The damping properties could be changed by varying the number and elasticity of the O-rings.

Maybe I'm wrong but the overall design doesn't look as if it has been through a demanding practical test.

[JHCC]

On 6/22/2016 at 6:18 AM, Bob_Nor said:

1. Ball peen hammer with round face, handle expands, but could be a bit thicker for the weight of the hammer

2. Diagonal peen hammer, good grip behind the head and at the end of the handle. The finish is a bit too smooth. The wood should offer quite good damping, it is soft and flexible.

3. Small ball peen with round face, good shape but a bit too thin

4. Soft ball peen, handle could have a bit more shape

Looks like straight peen, diagonal peen, small cross peen, soft cross peen to me. Am I missing something?

[Bob_Nor]

1 minute ago, JHCC said:

Looks like straight peen, diagonal peen, small cross peen, soft cross peen to me. Am I missing something?

Sorry, of cause you are right. I mixed up the expressions...

[JHCC]

The handles of my three main hammers. The one on the bottom (aka "The Beast") has been thinned down somewhat since this was taken, but needs a bit more. 

[SmoothBore]

Long, long ( 40+ years ) ago,... after breaking "yet another" sledgehammer handle, I set out to make a "bullet proof" sledgehammer.

I had made any number of "soft" hammers, by pouring #3 zinc alloy into a simple mold, and inserting a knurled bar for a handle.

Having access to a wide selection of "moly-steel end drops", ... and a fully equipped machine shop, ... it was a simple thing to "turn" a hammerhead, and knurl some pipe for handle.

So, ... I welded it all together, ... and hit something with it. 

That was quite the "learning experience." 

From that moment forward, I had a much clearer idea of the actual function of a hammer handle.

 

That horrible monstrosity is still laying around here somewhere, ... but I can guarantee that the head is still pristine and new.

Just thinking about it, still makes my hands sting.