YES! Let us SEE Nahum's treadle hammer. You keep teasing us with these descriptions! I'd like to post photos of Nahum's treadle hammer on my "others" page, if that's okay with you and Nahum.
(Maybe we should do a comparative test of treadle hammers: Smash a lead cylinder and see which hammer turns it into gold!)
It sounds from your description that Nahum hit upon a scheme rather similar to what I've hit on in the Grasshopper combined with what I've used in the Weightless Hammer.
To whit, if you use a weak spring (i.e., one with a low force-per-inch-stretched) you'll have to stretch it a LOT to simply support the ram. However, at this point the additional stretch needed to bring the ram down to the anvil will involve a relatively small increase in the spring force -- and hence rather little resistance to the foot. However, the consequent problem is that the spring may be so weak that it won't lift the ram back to the top quickly enough to be useful.
This problem is easily overcome by bottoming the hammer against another spring. By the time your ram hits your anvil, it's moving fast and has considerable momentum. If it bottoms out on a spring (of one sort or another) there will be little lost from this momentum, BUT the spring can exert enough force to push the ram back up to the top. That's exactly what I call "kickback" (in the Grasshopper).
From your description, it sounds like the main spring is not all that week in Nahum's hammer. To see hot to "weaken it" practically, visit my Weightless Hammer pages:
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In that design, I use an ordinary garage door spring against with a huge (~50:1) "mechanical disadvantage" (which is just "mechanical AD-vantage" worked backwards) so that the effect is of a weak spring stretched very far. (In the Weightless Hammer this is accomplished with a bicycle wheel "pulley" system. That is not the only possible means. For example, a block and tackle could achieve the same mechanical disadvantage if moment of inertia were not an issue.) Hence, the differential force from top to bottom of the stroke is very little. (There is almost no return force at all in the case of the Weightless Hammer. This hand-held hammer must be raised by the smith, but it "weighs" virtually nothing, so this is easy to do.)
I've gone one step better on the Grasshopper. By a mathematical analysis (that I wouldn't want to have to repeat) I determined that -- for the geometry of the Grasshopper mechanism -- I could virtually completely balance the ram by means of simple springs (NOT greatly extended, and hence less likely to fail catastrophically) and an excentrically mounted round pulley. This works well. However, as demonsrated by the Weightless Hammer, it is NOT absolutely necessary to achieve such perfect balancing of the ram. Beyond a certain point, you don't notice the difference anyway.
I, for one, would be very interested in what other improvements Nahum has made in his design. Much of the Grasshopper design (anvil, etc.) is obviously based upon Clay Spencer's design. There's much we can learn from what others have done.
Now, one more point. Time and time again folks have claimed the Grasshopper is SO SO complicated. I disagree. Yes, it uses two crankshafts in addition to the (typical) two hammer arms, plus a "grasshopper leg" strut. Big deal! As Cameron Stoker (see start of this thread) reports, his Grasshopper took about 50 hours to make. Not inconsiderable, but not excessive for a tool of this caliber.
MOST of the grousing seems to relate to the APPARENT complexity of the machine. It is for THAT reason that the Grasshopper plans and instructions are so complete. Every machined part is fully described in a separate engineering drawing, and every assembly has a corresponding engineering drawing, even including how and where to weld, and the order of assembly. Even the procedure for adjusting the Grasshopper, once assembled, is fully described. Cameron tells us he used the Grasshopper plans to train a newby in fabrication. Can't get much easier than that! (I never doubted the ease, however, since I was a newby myself, going into this development.)
At this point I must toss out that the Grasshopper plans are not currently available. I'm redesigning the kickback mechanism, and I will not reprint until that redesign is complete. The new design will be simpler to build AND to use. Namely, there will be one adjustment crank, not two, at the front of the machine, that will adjust the treadle height and the kickback simultaneously. (It took all these years for it to dawn on me that this was both desirable and easily possible! Good thing I can't literally kick myself in the head!) The prototype Grasshopper is now equipped with a prototype such adjustment that works well. I'm modifying the design further for good reasons and hope to improve it further. When I am satisfied with the redesigned kickback mechanism, I'll modify the Grasshopper plans and reissue them.
Bruce Freeman
BTW: Aren't babbitted bearings a bit complex ;^) for a treadle hammer?