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

The plans were taken from Shopnotes 1992 No2.

http://www.youtube.com/watch?v=t-j3UcfQ_rE

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.
Martin

On 2/17/2014 10:34 PM, wrote:
I made a mallet (deadblow?) from walnut, maple and BBs. Incredibly fun project.

The plans were taken from Shopnotes 1992 No2.

http://www.youtube.com/watch?v=t-j3UcfQ_rE

Subject

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

Lew

On 2/18/2014 12:40 AM, Martin Eastburn wrote:
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.
Martin

On 2/17/2014 10:34 PM, wrote:
I made a mallet (deadblow?) from walnut, maple and BBs. Incredibly
fun project.

The plans were taken from Shopnotes 1992 No2.

http://www.youtube.com/watch?v=t-j3UcfQ_rE


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

--
Jeff

On Tuesday, February 18, 2014 12:40:22 AM UTC-5, Martin Eastburn wrote:
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.


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.










Martin



On 2/17/2014 10:34 PM, wrote:

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



The plans were taken from Shopnotes 1992 No2.



http://www.youtube.com/watch?v=t-j3UcfQ_rE

On 2/18/2014 1:50 AM, wrote:
On Tuesday, February 18, 2014 12:40:22 AM UTC-5, Martin Eastburn wrote:
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.


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.










Martin



On 2/17/2014 10:34 PM, wrote:

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



The plans were taken from Shopnotes 1992 No2.



http://www.youtube.com/watch?v=t-j3UcfQ_rE




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.

--
Jeff

On Tuesday, February 18, 2014 1:55:33 AM UTC-5, woodchucker wrote:
On 2/18/2014 1:50 AM, wrote:

On Tuesday, February 18, 2014 12:40:22 AM UTC-5, Martin Eastburn wrote:

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.





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.





















Martin







On 2/17/2014 10:34 PM, wrote:



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







The plans were taken from Shopnotes 1992 No2.







http://www.youtube.com/watch?v=t-j3UcfQ_rE









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.

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.







--

Jeff

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.

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.

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.


http://www.hgtv.com/home-improvement...dex.html#dname
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.
--
Jim in NC


---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

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

The plans were taken from Shopnotes 1992 No2.

http://www.youtube.com/watch?v=t-j3UcfQ_rE

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

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.

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.

On 2/18/2014 9:15 AM, wrote:
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.

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.







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.

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.





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.

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!

On 2/18/2014 8:29 AM, 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

Yes. Thank you for the 'not'.

On 2/18/2014 10:11 AM, wrote:
Yes. Thank you for the 'not'.

LOL


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

In article ,
Morgans wrote:

various arguments about dead blow hammer design snipped...
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.



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?


--
There is always an easy solution to every human problem -- neat,
plausible, and wrong." (H L Mencken)

Larry W. - Baltimore Maryland - lwasserm(a)sdf. lonestar. org

In article ,
Leon lcb11211@swbelldotnet wrote:
oN 2/18/2014 9:15 AM, wrote:
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.

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.


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)

Larry W. - Baltimore Maryland - lwasserm(a)sdf. lonestar. org

On Monday, February 17, 2014 10:34:56 PM UTC-6, wrote:
I made a mallet (deadblow?) from walnut, maple and BBs. Incredibly fun project.



The plans were taken from Shopnotes 1992 No2.



http://www.youtube.com/watch?v=t-j3UcfQ_rE

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.

http://video.pbs.org/video/2365021538/

On 2/18/2014 6:09 PM, Larry W wrote:
In ,
Leonlcb11211@swbelldotnet wrote:
oN 2/18/2014 9:15 AM, wrote:
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.

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.


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.






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

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

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

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.

http://en.wikipedia.org/wiki/Impact_wrench

--

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

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

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.

http://en.wikipedia.org/wiki/Impact_wrench

Boy - this group can dive down into esoteric rabbit holes! Why doesn't
someone just try it rather than deliberating all of the theoretical
I-don't-really-know stuff?

--

-Mike-

On Tuesday, February 18, 2014 11:26:06 PM UTC-5, Mike Marlow wrote:
dpb wrote:

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

...



I don't know, I can hold the impact with a large enough socket, with

my bare hand, with a little slippage.



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.



http://en.wikipedia.org/wiki/Impact_wrench



Boy - this group can dive down into esoteric rabbit holes! Why doesn't

someone just try it rather than deliberating all of the theoretical

I-don't-really-know stuff?



--



-Mike-



It's physics. All of which can be extremely modeled with math w/o lifting a finger.

"Mike Marlow" wrote:
dpb wrote:
On 2/18/2014 7:00 PM, Leon wrote:
...

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

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.

http://en.wikipedia.org/wiki/Impact_wrench

Boy - this group can dive down into esoteric rabbit holes! Why doesn't
someone just try it rather than deliberating all of the theoretical
I-don't-really-know stuff?


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

Leon wrote:
"Mike Marlow" wrote:
dpb wrote:
On 2/18/2014 7:00 PM, Leon wrote:
...

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

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.

http://en.wikipedia.org/wiki/Impact_wrench

Boy - this group can dive down into esoteric rabbit holes! Why
doesn't someone just try it rather than deliberating all of the
theoretical I-don't-really-know stuff?


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

You get the beer prize then. I just sometimes find it funny how much we
kick ideas or thoughts around here instead of putting some of them to the
test. It does show we've got some thinking people here and sometimes I'm
downright amazed at what the guys here contribute, but still...

--

-Mike-

On 2/18/2014 10:26 PM, Mike Marlow wrote:
dpb wrote:
On 2/18/2014 7:00 PM, Leon wrote:
...

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

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.

http://en.wikipedia.org/wiki/Impact_wrench

Boy - this group can dive down into esoteric rabbit holes! Why doesn't
someone just try it rather than deliberating all of the theoretical
I-don't-really-know stuff?

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.

--

On 2/19/2014 6:19 AM, Mike Marlow wrote:

You get the beer prize then. I just sometimes find it funny how much we
kick ideas or thoughts around here instead of putting some of them to the
test. It does show we've got some thinking people here and sometimes I'm
downright amazed at what the guys here contribute, but still...

That's why it is invaluable, when either taking or giving advice, for
those seeking same to be able to see some actual evidence of the
advisor's skill and knowledge of that which he speaks.

IOW, thank dog for hypertext markup language and Sir Berners-Lee giving
some us the ability to do that when proffering advice.

All too often the advice proffered in forums like this are based on
Googled knowledge and damned little to none, actual experience.

--
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KarlCaillouet@ (the obvious)

On 2/19/2014 9:41 AM, Swingman wrote:
....

All too often the advice proffered in forums like this are based on
Googled knowledge and damned little to none, actual experience.

Well, being a "trained physicist" sometimes helps to understand the
underlying principles involved, too. Google did help find a
readable article, however, that outlines them...

--

dpb wrote:
On 2/19/2014 9:41 AM, Swingman wrote:
...

All too often the advice proffered in forums like this are based on
Googled knowledge and damned little to none, actual experience.

Well, being a "trained physicist" sometimes helps to understand the
underlying principles involved, too. Google did help find a
readable article, however, that outlines them...

Ok - I risk going out on a limb here, in areas that I'm not qualified to
speak into, but I do recognize your claim to credentials. What I have seen
many, many times is where there is some other consideration that the trained
eye failed to see. Not at all to downplay those credentials, but it is fair
to say that even the best design by the best engineering mind, falls prey to
the discovery of the prototype. You know - the oops moment when we realize
that we didn't recognize some aspect of the problem, or the likes. If
everything worked in the theoretical realm as it seems it should (as we see
it...), there would be no need for prototypes, proof of concept, testing,
etc.

Ok (again...), I lean towards the practical. I appreciate the theoretical
and in fact I value it greatly. But - I go to "just doing it" at some
point. Maybe that's just me, but it's the only way I can really prove the
theories behind what I'm doing.

--

-Mike-

On 2/19/2014 11:07 AM, Mike Marlow wrote:
....

Ok (again...), I lean towards the practical. I appreciate the theoretical
and in fact I value it greatly. But - I go to "just doing it" at some
point. Maybe that's just me, but it's the only way I can really prove the
theories behind what I'm doing.

Well, certainly I'll never claim every analysis I ever did was perfect
when taken to the lab w/o modification... (*)

OTOH, a prototype w/o some design basis in theory has a likelihood to
not be very successful, either, at least w/o a lot more testing effort
than could be necessary.

And, of course, the type of problem one's out to try to solve has a lot
to do with how much and how involved calculations needs must be. I only
tossed this one in here because the case of the impact wrench behavior
brought up isn't so apparent as to why since as Leon notes one can hold
it by hand yet it has the ability to break loose "frozen" fasteners that
simple leverage often can't. That seemed worth pointing as to what is
actually happening.

(*) Then again, they didn't give us a practice reactor to go run
experiments on before first criticality and power ascension; we had to
get it right from basic principles. Needless to say, there definitely
were some tight muscles in certain areas when that day came...but, turns
out theory correctly applied _does_ work and we hit hot zero power
criticality soluble boron concentration within about 10 ppm of the
computed value (1190 vs 1200).

--

On 2/19/2014 10:00 AM, dpb wrote:
On 2/19/2014 9:41 AM, Swingman wrote:

All too often the advice proffered in forums like this are based on
Googled knowledge and damned little to none, actual experience.

Well, being a "trained physicist" sometimes helps to understand the
underlying principles involved, too.

No worries, those who are trained in just about any scientific
discipline are generally quite capable of recognizing the same in others
of very different disciplines, Google notwithstanding. g

That fact might have a time limit on it though ...

--
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KarlCaillouet@ (the obvious)

On 2/19/2014 4:12 PM, Swingman wrote:
....

No worries, those who are trained in just about any scientific
discipline are generally quite capable of recognizing the same in others
of very different disciplines, Google notwithstanding. g

That fact might have a time limit on it though ...

If that's referring to what I'm presuming, I'm forgetting more and at a
more rapid rate every day, too...

A fellow at the morning coffee klatch the other morning had seen a Nova
program with Brian Greene wherein he had apparently (I didn't see it)
mentioned getting interested in physics in HS when he realized could
write equations for complex systems and solve for the resulting motion.
I guess the example was the HS physics instructor hypothesized a
baseball stuck to the ceiling w/ a wad of gum and what would happen?

After the obligatory explanation of Newton (the fellow's a geologist,
not an engineer so his physics is even rustier than mine), I explained
how there's an easier formulation altho I doubted that even Dr Greene
knew anything about it at the HS level. So, I started to write the
Lagrangian show him how to set up the two coordinates of angle and
vertical displacement and then...and then...and then...

Just been too long. So, anyway, I've spent the evenings last week or so
after that humbling experience glancing thru a couple old texts again
while the Olympics bumbles along in the background...

One thing is clear...the practice w/ the modern computer and things such
as Matlab, Mathematica, and all the other engineering toolsets is a far
cry from the early days when was issued the 20" K+E slide rule when
first reported for duty at B&W NPGD...

--

On 2/19/2014 4:41 PM, dpb wrote:

One thing is clear...the practice w/ the modern computer and things such
as Matlab, Mathematica, and all the other engineering toolsets is a far
cry from the early days when was issued the 20" K+E slide rule when
first reported for duty at B&W NPGD...

Last couple of semesters of college making up for lost time with as many
math courses as I could handle, my slide rule skills were like a sharp
pencil when I was drafted into the Army. As a young Fire Direction
Officer, I had no trouble routinely sending commands to the guns before
our computerized system cleared its buffers.

Today, I'd have a hard time using one to stir my coffee ...

--
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http://www.custommade.com/by/ewoodshop/
KarlCaillouet@ (the obvious)

I hate to keep kicking this horse but... I just received my electronic issue if Popular Woidworking today. An article on mallets was on the inside. What a coinkydink.

On the topic of dead blows the cabal says:

"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

On 2/20/2014 10:47 AM, wrote:
I hate to keep kicking this horse but... I just received my electronic issue if Popular Woidworking today. An article on mallets was on the inside. What a coinkydink.

On the topic of dead blows the cabal says:

"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








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.

On 2/20/2014 10:47 AM, wrote:
I hate to keep kicking this horse but... I just received my
electronic issue if Popular Woidworking today. An article on mallets
was on theinside. What a coinkydink.

On the topic of dead blows the cabal says:

"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? ...

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...

--

What I don't understand in particular are these two phenomena that would seem 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 does, 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 energy 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?

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

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

On 2/20/2014 2:23 PM, wrote:
*Should be "of equal mass and close mass distribution"

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

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.

On 2/20/2014 1:29 PM, wrote:
What I don't understand in particular are these two phenomena that would seem 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 does, 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 energy 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?

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...

--

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.