[TheForge] treadle hammer design (was:
treadlehammeranvils)
Bruce Freeman
[email protected]
Fri Jan 24 19:18:01 2003
Randy,
Right! You'd STILL need a snappy spring to provide return force. The =
counterbalancing alone won't do it. =20
But in addition, you would have to have really tight pivot bearings to =
ensure that the counterweight mass would add to the ram mass in providing =
the blow. Any slop anywhere and you'd lose impact force.
Bruce
NJ
>>> [email protected] 01/23/03 02:54PM >>>
I built a treadle hammer from the ABANA plans a few years ago , at that =
time
I also thought about a counter ballance arrangment. It sure seems like two
25lb weights on either end of an arm would move as fast as one 50lb wt on
one end. Of course you would need enough spring tension to raise the =
hammer
rappidly, this not just a balancing act. If the arm between the weights =
was
a leaf spring it might add some life to the whole affair.
Randy Mundt
----- Original Message -----
From: "Bruce Freeman" <[email protected]>
To: <[email protected]>
Sent: Thursday, January 23, 2003 7:18 AM
Subject: Re: [TheForge] treadle hammer design (was: treadlehammeranvils)
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.
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=20
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=20
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.
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.
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=20
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
much heavier frame and base plate as well as a massive pivot mechanism =
and
lever arm...thought about making the weight adjustable along the arm.
The advantages would be, not only double mass, but also a slower, more
penetrating blow. Disadvantages would include slower BPM , cost and loss =
of
portability...cause you sure would have to tie that dog down.
>I have looked at the designs of several different styles of treadle
>hammer. And they all seem to have one thing in common, some sort of =
lever
>and large springs which lift the hammer, and a treadle to over come the
>springs and lower the hammer. So I ask, what would be the result if the
>springs were replaced with a weight great enough to balance the
>hammer. Then a light spring could lift the hammer. Say a conventional
>design has a hammer of 50# and the operator can accelerate that weight to
>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
>balanced, say 25# hammer and 25# counterweight, would it not strike at =
the
>same pounds per sq. inch when moving at 5 fps?
>This does require the ram and the weight be rigid to each other. The
>point being is that you still have 50# of mass in motion, and the energy
>is transferred in the blow, not in the motion of the head. Seems
>somewhere it is written that a mass in motion will remain in motion, or
>something like that. Just something to think about. I'm sure I am over
>looking some obvious law of physics that says this is not how things =
work.
>
>Larry
>
>
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