Make a Mallet (Shopnotes)

[Leon]

Well actually, as indicated with one of my last reply, I have tried it.

[dpb]

Not really so esoteric at all...it's the explanation for _why_ Leon's experience is so....that seems at best at least counter-intuitive on first blush.

[brian]

"Minimal rebound makes better use of the applied force"

How do I get a better use of force here? How did this myth start? I want to blame someone. Norm? Can I blame Norm? :)

Again if F = ma. And I apply the m a little at a time apposed to all at once, how is this a better use of the applied force? I think we officially debunked Leon's hammer driver explanation :)

[Leon]

Probably thinking one thing and saying another. With a dead blow you don't have to worry about the the hammer bounce back coming and hitting you in the head. ;~) Consequently you can bang harder and not worry that so much.

[dpb]

want to blame someone. Norm? Can I blame Norm? :)

You _really_ don't want to get more into the physics of hammers, trust me... :)

But, besides the conservation of energy, there's conservation of momentum to be considered and the transfer of energy from/to the target is also a dependent on the characteristics of both the driver head and the target.

And, the actual force is an impulse wherein the motion of the hammer comes to rest in a distance that is dependent on the resistance of the target--the more resistant, the shorter the distance moved and the higher the delivered force because that resisting force times the moved distance must be the same as the kinetic in the hammer to balance the energy.

A well-designed dead-blow hammer has most of the mass in the head in the innards so the actual head has essentially come to rest when the internal mass then delivers the blow. The effectiveness comes from the more effective transfer and less recoil energy that doesn't go into the target with a conventional hammer head.

And, that's all I'm going to say and I'm _not_ going to go into a full-blown analysis...if I still had access to a nonliner FEA system I might be inclined to set up a couple or three examples that could show what happens w/o having to actually set up the detailed analytical solution, but having returned to the farm from the consulting gig I don't. It's a lot like a simplified case of the collision analyses the major auto manufacturers go through where they actually use such to help design survivability into their vehicles...

[brian]

What I don't understand in particular are these two phenomena that would se em to reduce the effectiveness of the applied mass:

1) when the deadblow is accerated toward the object the mass (majority) is in the rear of the cavity (from inertia). After the deadblow makes contact the mass leaves the rear of the cavity and travels to the from and as it d oes, it decelerates. (Loss of a thus loss of efficiency)

2) there is still bounce back inside the deadblow head. After the shot is thrown against the front inside of the deadblow it will bounce back. The e nergy that is lost to internal bounce back should equal any energy lost to the bounce back of a non-deadblow mallet of equal mass. Correct?

[brian]

*Should be "of equal mass and close mass distribution"

And please don't swap the terms. Recoil? Leon likes the term bounce back :)

[Leon]

Bounce back = Energy that is not entirely absorbed by the strike and which is deflected.

Recoil is a good term. Not all of the energy spent inside a bullet is pushing the bullet down the barrel, much is absorbed by the person shooting the gun.

[dpb]

Both, essentially, "no" with a proper choice of materials and construction. 1) doesn't decelerate except by hitting the head (albeit some indirectly thru the elements ahead of them) to any appreciable extent. The benefit comes from the marked difference in recoil energy lost. The internals don't act as does a solid; it's that elastic/inelastic thingie again...

[brian]

But you still have deceleration. A point that gets at the increased efficiency claim. The magnitude can certainly be debated.

I'm not sold on the increased efficiency from a better recoil property for the shot. It's still going to recoil. Bang into each other (energy loss) and bang into the sides of the cavity (energy loss)

You also have a loss in energy via heat (from banging into each other) that doesn't come into play on a solid hammer of equal mass. Again, this gets to efficiency. Magnitude can be debated.

I don't think we get a free lunch here. More efficiency from a hammer strike with the same amount of mass - not convinced.

[Morgans]

Look at the swing as a closed energy system. If the hammer bounces back, that energy came "from somewhere." It came from not driving the object being struck. When there is no bounce, all of the energy (minus a very small amount of friction of the shot heating up) gets expended driving the struck object. That is the only way you can look at it.

[brian]

There is bounce. That's my point. The "bouncing" is occurring on the inside of the cavity. A ball dropped from one end of a cavity to the other is going to bounce.

[dpb]

On 2/20/2014 2:59 PM, [e-mail] wrote: ...

They're _not_ the same system and that _does_ make a difference in how they behave.

[Leon]

The mallet head striking an object bounces. The shot hitting the opposite end of the mallet when the mallet bounces back "helps" to cancel out the head bounce back.

[none]

On Thu, 20 Feb 2014 16:06:50 -0600, Leon

Pretty much as I'd have explained it. But however one looks at it, a dead blow mallet is a damned useful tool. You don't really realize it though until you actually use one.

[Leon]

Now I will say........ I had a dead blow mallet back in the 70's. It eventually degraded and the plastic disintegrated and left the steel handle and a shot gun shell sized capsule partially filled with the pellets.

I suspect that a lot of the bounce back is also absorbed by the plastic material that is used to encase the steel parts.

For the past 20 or so years I have used one of those smaller hammers with a red rubber face on one end and a yellow plastic face on the other. The plastic face end is a similar plastic that is used on the dead blow mallets. My current non dead blow hammer does not have much bounce back either....

[brian]

inside of the cavity. A ball dropped from one end of a cavity to the other is going to bounce.

It helps to cancel out the mallet bouncing back. I'm not arguing this poin t. We agree here.

There is bouncing in either case that results in an energy loss. This does n't address the deadblow's claimed increase in efficiency.

Hundreds (arbitrary) of shots smacking into the bottom of a cavity or a sho t filled cavity are going to bounce and bang around. The sum loss in energ y from the bounce back (including any collisions between each other) of eac h shot is going to be significant.

If you were to compare the efficiency of a deadblow's strike and a mallet o f equal mass and size (shot filled w/ no empty space), and take into accoun t the above, I wouldn't expect an increase in efficiency from the deadblow.

[brian]

Agreed. They behave differently and I touched on the differences in length.

[none]

On Thu, 20 Feb 2014 16:56:54 -0600, Leon

This is the one I have.

[Lew Hodgett]

---------------------------------------------------------------- When it's time to replace, HF is your place.

About $5 for the equivalent.

Lew