Make a Mallet (Shopnotes)

Page 2 of 4  


Well actually, as indicated with one of my last reply, I have tried it.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 2/18/2014 10:26 PM, Mike Marlow wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Monday, February 17, 2014 10:34:56 PM UTC-6, snipped-for-privacy@garagewoodworks.com wrote:

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/
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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 :)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 2/20/2014 10:47 AM, snipped-for-privacy@garagewoodworks.com wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 2/20/2014 10:47 AM, snipped-for-privacy@garagewoodworks.com wrote:

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...
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
*Should be "of equal mass and close mass distribution"
And please don't swap the terms. Recoil? Leon likes the term bounce back :)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 2/20/2014 2:23 PM, snipped-for-privacy@garagewoodworks.com wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Right. Energy that isn't absorbed is useless, however that which isn't moving the struck object is just being absorbed uselessly as heat anyway. I don't see that the lack of "bounce" necessarily makes the hammer more "efficient". It just means it's absorbing energy, rather than the user's arm.

Newton's third law kinda makes this a given.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Friday, February 21, 2014 6:22:15 PM UTC-5, snipped-for-privacy@attt.bizz wrote:

It doesn't.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It also depends on your definition of what an "efficient" hammer blow is and what its purpose is. If I remember my physics right, there actually is a _greater_ transfer of kinetic energy to the strcuk object when the striking object rebounds. Conservation of momementum demands it. On the other hand, that's based on "inelastic" objects and and when there's deformation then things are calculated differently.
Maybe the deformation is what you're after, rather than kinetic energy transfer. I've been away from the math of physics for too long to figure out or remember how this translates for instance into driving a tenon into a mortise or other common tasks. I'm sure one of our engineer participants will address this soon enough. :)
--
Make it as simple as possible, but not simpler. (Albert Einstein)

Larry W. - Baltimore Maryland - lwasserm(a)sdf. lonestar. org
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 22 Feb 2014 00:52:14 +0000 (UTC), snipped-for-privacy@sdf.lonestar.org (Larry W) wrote:

You just contradicted yourself. There is *not* a greater transfer of energy if the hammer rebounds. The energy required for the rebound is not imparted to the object, which is sorta the purpose of striking it in the first place. There is no such thing as conservation of momentum, in this case. There is *always* conservation of (matter and) energy.

Deformation is kinetic energy transfer. You're converting the kinetic energy into heat (still kinetic energy with perhaps some potential energy in a chemical/physical state change).

It all turns into heat. ;-) You're trading the kinetic energy from the hammer into heat from friction (heat/kinetic energy) of the mortise into it's tenon.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

What he said. Where did the energy for the mallet come from to make it reverse direction. From the object being struck not soaking up all the energy. Been saying that all along.
This horse is about dead, isn't it?
--
Jim in NC


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 22 Feb 2014 16:28:52 -0500, "Morgans"

That said, because it doesn't rebound doesn't mean that it did its job, either. If the energy is absorbed in the hammer's head (heat), it's not doing much good either. Of course, if it dents the paint on your just completed cherry table, it isn't doing its job either. ;-)

You're supposed to put the glue on the tenon _before_ pounding it into the mortise.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Check out the math. If we're talking about kinetic energy and conservation of momentum, more will be transferred to the struck object in an elastic collision, where the striking object by definition is free to rebound and there is no permanent deformation of either object. Of course, most of the time in woodworking, we're NOT talking about an elastic collision and it's not what we want either.
--
Often wrong, never in doubt.

Larry W. - Baltimore Maryland - lwasserm(a)sdf. lonestar. org
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 2/20/2014 1:29 PM, snipped-for-privacy@garagewoodworks.com wrote:

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...
--




Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.
--
Jim in NC


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.