[TheForge] treadle hammer design (was:
treadlehammeranvils)
Bruce Freeman
[email protected]
Thu Jan 23 13:17:00 2003
Larry,
I'm not absolutely sure I follow you, especially about that trap door, but =
I think what you mean by "the acceleration aspect that becomes a problem" =
is the fact that the user has to accelerate the ram, rather than gravity =
doing it. Obviously true. =20
But not a problem at all.
It simply is not that difficult to accelerate a weightless mass. We =
accelerate hand-held hammers all the time. See how much work you get from =
a hand-held hammer if you let gravity do all the accelerating. Not much! =
So we typically fling hammers down on our work with considerable accelerati=
on.
Having worked a bit with a weightless 16-lb sledgehammer, I can assure =
you that even accelerating that without gravity's help is no big deal. =20
Now, accelerating a 50-70-lb ram with your foot is no big deal either.
Bruce
NJ
>>> [email protected] 01/23/03 11:38AM >>>
Hi Bruce, Pete,
I thought about the speed thing, it is the acceleration aspect that =
becomes a problem. Some thing about a mass at rest........ I thought =
about using a pulley arrangement where one end anchors to the frame and =
the other to the ram or some where between and the pulley to the treadle. =
I think this is how you did the grasshopper. At any rate it works well on =
a trap door for one of my shops. I can see that when the ram is moving =
with gravity then acceleration occurs naturally, and when the weight is =
moving both up and down
then the task of acceleration becomes completely upon the operator. Hence =
the slow moving ram. In as much as speed =3D impact force, I see where =
this becomes the factor in limiting efficiency. More thought must be =
applied. Thanks for your insights and experience. Maybe with a little =
combined effort, we can like this dog yet.
Larry
Bruce Freeman wrote:
> 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 accelerati=
on. 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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