Make a Mallet (Shopnotes)

[brian]

I made a mallet (deadblow?) from walnut, maple and BBs. Incredibly fun project.

The plans were taken from Shopnotes 1992 No2.

[Martin Eastburn]

[Lew Hodgett]

RE: Subject

See abpw for a similar unit I made, but without metal balls.

Lew

[woodchucker]

Looks good, but I would agree with Martin, also I might use lead shot to increase the weight with less fill.

[brian]

Not convinced. Here's why:

F = ma : Half full gives me approx F = 1/2 ma

"Many hammer blows" : Force = ma (collission1) + ma (collisions2) ... etc. = m(total)a

You only end up with approx 1/2 the amount of force as a full hammer head spread out over multiple smaller collisions. The sum of which are still 1/2 a full head.

[woodchucker]

So I was wrong, I thought Martin was talking about the bounce back. With a full head, you gain mass, but I don't think it gives you the deadblow, that is desireable. That's why I would go with less fill, but lead, to gain back the mass.

[brian]

No. Substitute the mass for lead in my equations above. You are still better off with a full head of lead than 1/2 full head of lead. It's the same equations.

[Morgans]

What you are describing is a weighted mallet. For a deadblow hammer to be effective, the shot moves to the back of the hammer as you start to swing, then crashes forward at impact, thus reducing rebound. It can not shift if it is full. See the definition, here.

dead-blow hammer Strikes blows without damaging the work's surface. The tool's hollow head is partially filled with small metal shot, which reduces rebounding.

[Leon]

Nice looking mallet!

BUT with no internal loose mass, your answer about " deadblow?", would be no, not until the bb's slowly deform the cylinders and have more room to move to give the secondary amount of force to help counteract bounce back. The more movement the more counteraction to bounce back you will have.

Having said that, walnut being significantly softer than maple might itself cushion/absorb some of the impact and lessen the bounce back if you don't strike squarely or until the walnut rounds off or splits off.

If you are building these for a conversation piece, the walnut looks very nice. For actual use I would recommend that the striking faces be of equal hardness. As the softer material mixed with a harder material wears away faster the striking surface naturally becomes smaller and the force is concentrated in a smaller area. This might leave an unwanted impression on a wood surface if you are using the mallet for adjustments. That particular use is what deadblows excel at.

If you used a heavier material, walnut is pretty lite weight, with less loose mass internally you benefit more with more counteraction to bounce back.

Now let me throw you a curve on your "force calculation". First off your equation does seem logical. BUT an impact driver delivers more efficient force than does a drill/driver with the same available power supply. It's the multiple impacts of the impact driver that wins the contest of loosening the stuck screw vs. the constant force of the drill/ driver.. So while loose shot in a dead blow hammer might seem to have less force at initial impact the amount of work being done is probably close to the same given the second impact force of the loose shot. That is going to be hard to formulate given some loss from the secondary force counteracting the bounce back. Maybe if the entire mallet striking surface was walnut the bounce back would be diminished. Whew! :-). Something to think about. LOL

[brian]

ok. Then what i have is a mallet and I named it correctly. I'm concerned with the mallet head bouncing back. I'd rather strike fewer times with more force than more times with less bounce back.

[brian]

Consider this:

A large force that is delivered in smaller doses is not as efficient at driving a joint home as one force all at once.

Each smaller force would have to first overcome the coefficient of friction before it can move an object. Any small fraction of the force that is below the coefficient of friction is a loss.

Consider the extreme : dropping 100 kg of lead weights on a stuck joint at a 1g at a time versus dropping the 100 kg all at once. If the 1g force doesn't break the coefficient of friction you will have very little net joint closure.

[Leon]

Perhaps in theory. but in real life, the impact driver works with multiple lighter strength impacts. Its the multiple impacts that produce more work in a given period of time. A larger single force may be way too much or simply not enough.

Agreed there is that, but addressing the deadblow that you mentioned, the loose shot works more to dampen the bounce back rather to increase force. There are all kinds of factors to consider here. The loose shot's main function is really not to increase the driving force. Your adding of the loose BB's to fill the void was more of a convenience to add mass than to add the feature of a dead blow mallet. You have to have the second impact of loose shot to tweak the mallet to have dead blow characteristics.

That is correct however in a dead blow hammer the loose shot weight does not have that extreme of a difference to the rest of the hammer head as the 100 to 1 ratio.

I think your reference to the mallet possibly acting like a deadblow was whet most of the replies were questioning.

I was just throwing the countless possibilities to be factored in to get different affects depending on the size of the shot, weight of the shot, shot weight ratio, size and shape of the shot chamber... ;~) Just something to think about. ;~)

Either way your mallet looks really cool!

[Leon]

Probably "not" concerned with the mallet bouncing back....

With that thought you have exactly what you were going for.

Imagine using mercury for the weight, I wonder if it would leak out. LOL

[brian]

Yes. Thank you for the 'not'. :)

[Leon]

LOL

Welcome to MY world. Thinking one thing, typing something else all together.

[Larry W]

Make the hammer twice as big, using equivalent of a full load of shot from the original smaller size, for the best of both worlds? :)

[Larry W]

I believe the flaw to that argument is that an impact driver in fact does NOT use multiple lighter strength impacts, but actually, due to the nature of impact, uses momentarily HIGHER forces than the static tool torque spec would imply.

[Michael]

It looks great but I think a solid head where you drill, fill, and cap on both sides would be more useful. Also, why not taper the mortise and insert the handle end first so that it gets more snug the further you pull it through?

Here's Roy Underhill getting it done.

[Leon]

I don't know, I can hold the impact with a large enough socket, with my bare hand, with a little slippage.

[dpb]

On 2/18/2014 7:00 PM, Leon wrote: ...

Because impact wrenches don't actually deliver torque, per se, but an energy impulse. Somewhat paradoxically, against a "springy" resistance like your hand, there is very little, if any actual torque delivered as opposed to it working against a stuck fastener.

There's a decent albeit not fully rigorous discussion at wikipedia under a heading "Effect of Impact Drive"...in short to transfer the hammer action to the driven part requires an essentially elastic (the cue ball on the object ball thingie) impact whereas your hand hold is very non-elastic.