[TheForge] treadle hammer design (was: treadle hammeranvils)

Thu Jan 23 09:46:00 2003

Larry and Artgawk(?):

Good thinking, but I'm ahead of you on this one.

I actually tried a counterbalanced hammer back in 1997 or so.  (It might =
have worked as a treadle hammer, but I had rigged it up as a hand-held =
hammer.) With RIGID connections (including no slop in the pivots) such a =
machine might work, but it was my impression that Artgawk's (OK, what's =
your REAL name?) intuition about slower BPM is right on.  The thing moved =
VERY slowly.  So slowly, that all advantage of using a heavy hammer was =
lost.=20

In that respect, please consider that momentum =3D m*v, but work =3D =
energy =3D mv^2 =3D (m * v-squared); where m =3D hammer mass and v =3D =
hammer velocity at impact.  Hence the speed of the hammer is (within =
limits) much more important than the mass.  (Useful work is a different =
concept:  A bullet may do more "work" than a single blow from a power =
hammer, but I don't see anyone changing over to machine-gun smithing!)  I =
readily demonstrated to myself that a slow-moving 16# slegehammer was MUCH =
less useful than a hand-held 2-lb hammer.

In designing the Weightless Hammer (a hand-held sledgehammer), I overcame =
this speed problem by using a 24"/4" pulley(-sprocket) speed increaser.  =
Although the Weightless hammer employs a garage-door spring to balance the =
hammer, the concept works just as well with a heavy weight (16 lb. x 24" / =
5" =3D ~100 lb) (but is a lot more awkward and less portable).  This =
works:

http://www.monmouth.com/~freeman/wh/wh.htm

Responding to Larry's original post:  I previously designed a more elegant =
weightless treadle hammer, namely the Grasshopper Treadle Hammer:

http://www.monmouth.com/~freeman/bmf/grashopr.htm

In this case I still use (4) garage door springs to balance the weight of =
the ram.  Again, this is mostly for practical reasons.  A weight would =
have been easier to design in (as it doesn't change its force as it =
changes position) but I would probably have needed a several-hundred-pound =
weight for the purpose. =20

I went one step further here.  You don't really need ANY continuous spring =
force to lift a weightless ram.  You only need an initial acceleration.  =
In an ideal world, the bounce you get when the ram hits the anvil might be =
enough.  However, you can't count on that, especially when some hot metal =
will absorb all the impact.  Therefore, I designed in an adjustable =
"kickback" force mechanism. =20

This kickback mechanism is equivalent to the ram - a the bottom of its =
stroke - coming down on and compressing a short, light spring.  When the =
momentum of the ram was dissipated in the work, this spring would then =
push the ram back up, but the push would only be for a short time.  =
However, "an object in motion tends to remain in motion," so this is =
sufficient to carry the ram all the way back up.

The action of this mechanism is clear in the animation:
http://www.monmouth.com/~freeman/bmf/GHanimNW.htm

Enjoy,

Bruce Freeman
Nj

>>> [email protected] 01/23/03 04:02AM >>>
At 02:29 PM 1/22/03, you wrote:

Thought about doing the same thing. Figured that the set up would require =
a=20
much heavier frame and base plate as well as  a massive pivot mechanism =
and=20
lever arm...thought about making the weight adjustable along the arm.
The advantages would be, not only double mass, but also a slower, more=20
penetrating blow. Disadvantages would include slower BPM , cost and loss =
of=20
portability...cause you sure would have to tie that dog down.

>I have looked at the designs of several different styles of treadle=20
>hammer.  And they all seem to have one thing in common, some sort of =
lever=20
>and large springs which lift the hammer, and a treadle to over come =
the=20
>springs and lower the hammer.  So I ask, what would be the result if =
the=20
>springs were replaced with a weight great enough to balance the=20
>hammer.  Then a light spring could lift the hammer.  Say a conventional=20=

>design has a hammer of 50# and the operator can accelerate that weight =
to=20
>say 5 fps and the travel is 8 inches.  You would have an
>impact of XXX pounds per sq. inch.  If you had a hammer where the head =
was=20
>balanced, say 25# hammer and 25# counterweight, would it not strike at =
the=20
>same pounds per sq. inch when moving at 5 fps?
>This does require the ram and the weight be rigid to each other.  The=20
>point being is that you still have 50# of mass in motion, and the =
energy=20
>is transferred in the blow, not in the motion of the head.  Seems=20
>somewhere it is written that a mass in motion will remain in motion, =
or=20
>something like that.   Just something to think about.  I'm sure I am =
over=20
>looking some obvious law of physics that says this is not how things =
work.
>
>Larry
>
>
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