[TheForge] "DROP" Hammer - Bounce vs. dead drop

[Bruce Freeman]

Actually, it may be more beneficial than that, even.  

The force delivered to the struck object is equal to the change in momentum divided by the duration (time) of the collision.   Momentum is mass times velocity.  The change in momentum is the initial momentum minus the final momentum * but since momentum is a vector quantity (i.e., it has direction) subtracting an upward ("negative") momentum from a downward ("positive") momentum is really ADDING the ("scalar") momenta.

Hence, a hammer delivers more force when it bounces than when it hits dead.  (This may seem counterintuitive, but it's what a "live" anvil is all about.)

The other factor of considerable importance is the collision duration.  If the collision is quick, then the force is higher.  If slow, the force is lower.  The collision duration is not an easily definable thing, but may be considered the time between first and last contact.  Deformation of hammer, anvil or object will increase the collision duration and reduce the force of the collision.

Bruce
NJ


>>> mrscherm at aol.com 10/5/2005 8:56:45 AM >>>
With conventional (commercially used) drop hammers, the "bounce" is a 
real advantage, as it becomes the start of the next stroke, i.e., the 
bounce in essence overcomes the inertia and provides the start of the 
lift of the die to it's "up" position for the next blow, thereby 
greatly easing the workload of the lift mechanism.
Michael

-----Original Message-----
From: Bruce Freeman <FREEMAB at pt.fdah.com>
To: theforge at mailman.qth.net 
Sent: Wed, 05 Oct 2005 08:07:49 -0400
Subject: [TheForge] "DROP" Hammer - Question

I've been wondering for some time about that idea - loose lead fill in 
a hollow
hammer. Seems to me that only would only work in a "driven" (e.g., 
hand-held
dead-blow) hammer.

I would gusss that, in a drop hammer, everything (hammer and lead fill) 
would be
falling at the same speed. Unless compression of the fill were 
involved, there
would be no less tendency to bounce. But then, I've never tried it.

Bruce
NJ

>>> lughaid at earthlink.net 10/4/2005 4:20:09 PM >>>
Yup, I used to work with Michael Stewart at Quick Silver Minting,
Tool and Die. We made the crank up drop hammer you saw, and quite a
few others. Hammer head is a well casing with a 3 inch plate welded
to the base, capped and filled with lead shot. about 125 pounds head
weight for a dead drop to keep from double striking the
"coins".


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