As I posted, I'd use a 50% fill of BB's - the video shows 100% fill.
You want the many hammer blows when you smack something.
On 2/17/2014 10:34 PM, firstname.lastname@example.org wrote:
On Tuesday, February 18, 2014 12:40:22 AM UTC-5, Martin Eastburn wrote:
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.
On 2/18/2014 1:50 AM, email@example.com wrote:
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.
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.
Strikes blows without damaging the work's surface. The tool's hollow head is
partially filled with small metal shot, which reduces rebounding.
On 2/18/2014 8:29 AM, firstname.lastname@example.org wrote:
> 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.
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
On Mon, 17 Feb 2014 22:50:28 -0800 (PST), email@example.com wrote:
But you have ended up with a sledge hammer, not a dead blow.
A proper dead blow transfers all its force and no bounce back. You can hit
it as hard as you can on a concrete floor and it just "sits" there.
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
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.
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.
On 2/18/2014 9:15 AM, firstname.lastname@example.org wrote:
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
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!
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.
There is always an easy solution to every human problem -- neat,
plausible, and wrong." (H L Mencken)
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
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