[TheForge] treadle hammer design (was:
treadlehammeranvils)
Bruce Freeman
[email protected]
Fri Jan 24 19:18:07 2003
Marc,
First, without regard to the "why" question, it is my observation based =
upon real tests that a see-saw hammer is slow. "Experimental observation."=
Now, let's see what we're comparing. No question that putting one 25-lb =
child on each end of a see-saw will result in a balance, or weightless, =
condition. But how fast does a see-saw move? Ever see one move real =
fast?
To get motion out of it at all, there would have to be some degree of =
IMbalance when the hammer was at the anvil. The opposite weight would =
have to provide a return force. =20
(As I mentioned earlier, this can be done by using a see-saw bent downward =
at the pivot point. Hence lowering the hammer is lifting the weight, and =
they are out of sync. so there WILL be a return force by the time the =
hammer hits the anvil.)
The problem is that if that is a SMALL force (because most of the =
counterweight is still balancing the hammer) the acceleration will be low, =
and the hammer will not move fast. It's not that it couldn't be MOVED =
fast, it's that there isn't the force to do it.
Remeber that we're comparing this to a spring. By the time we strike the =
anvil with the ram of a treadle hammer, the spring is stretched a good =
deal and provides a snappy return force. Unfortunately WE really provide =
that force in stretching the spring in the first place =AF that's the =
problem we're trying to fix here. The ram is NOT at "near-zero" gravity =
when it hits the ram. It's at a substantial NEGATIVE "gravity" (=3D =
spring force).
Did I make that clear?
BTW, for the two 25-lb weights to add to 50 in effect, it would be =
essential to have zero slop in your pivot bearings and all other links. =
Otherwise at best you'd get a dead-blow hammer of 50 lb total.
Bruce
NJ
>>> [email protected] 01/23/03 01:37PM >>>
I've been following this thread and need some clarification on why a
counterbalanced hammer would be slower than a spring return one.=20
The original question asked if, instead of a 50lb ram, you had a 25lb
ram with a 25lb counterweight. The mass stays the same, so, not counting
gravity, the same acceleration would take the same force. And it would
then result in the same hitting force.
If you throw gravity at it, yes, you have to "lift" the counterweight,
but you also have to stretch the springs. The net desired effect is to
have the hammer at near-zero gravity in both situations. So gravity is
canceled out.
I'm not refuting any claims, just need to understand. I've got a degree
in EE, so that naturally makes me an expert in all things scientific :-)
-Marc
On Thu, 2003-01-23 at 12:06, Bruce Freeman wrote:
> Larry,
>=20
> 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
>=20
> But not a problem at all.
>=20
> 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.
>=20
> 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
>=20
> Now, accelerating a 50-70-lb ram with your foot is no big deal either.
>=20
> Bruce
> NJ
>=20
> >>> [email protected] 01/23/03 11:38AM >>>
> Hi Bruce, Pete,
>=20
> 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
>=20
> 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.
>=20
> Larry
>=20
> Bruce Freeman wrote:
>=20
> > 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),=20
>=20
>=20
--=20
Marc Godbout
http://www.ironringforge.com=20
New England Blacksmiths Membership Director
http://www.newenglandblacksmiths.org=20
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