Reply by RobynHoodridge

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Posted on Shaving Giraffe - a shave horse re-design from Africa

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127 posts in 2355 days

#1 posted 01-30-2013 11:42 AM

Ooh, great point to bring up.
I’ll probably end up re-phrasing what you said so succinctly. If I do, it’s just to help explain, especially to those reading who haven’t already thought on this.

I probably talked about pushing with your legs shifting you because I imagine really having to bear down on the foot pedal to keep the stock still for some tasks. And especially if the perpendicular (normal) force in equal and opposite reaction to this hefty pushing is angled somewhat upward through your leg, it seems it would want to push you up and out of your seat backward. Obviously not a major issue with shaving horses, since they function and function well. And I may be entirely wrong about that scenario.
So at the same time I think you’re absolutely right, the rowing action against (or braced by) your legs is probably vital. Else you’d flop forward, rotating at the seat, if you were using a drawknife. Luckily you could still use your legs this way at the Giraffe. Only, pushing against the ground.
I imagine two scenes when you mention your trial at the out-feed table. In one you’re sitting on a chair or stool and get pulled horizontally toward the work and directly in line with it, rather than shaving it. (Your chair even has wheels in my head.) Because as you rightly say, there’s nothing to stop that. However, on a shaving bench (whatever kind) you’re attached to it in at least one place. You’re sitting on the very thing you’re pulling against.
(i’m certain this isn’t what you’re concerned about, but bear with me)

Being ‘attached’ to the structure you’re pulling on becomes especially handy when you’re not just pulling horizontally and relying on friction to act against a horizontal force. And this is the main ‘trick’ of the shaving bench design. It’s clamping platform is angled upward from the horizontal. Gives a better action of your arms movements, but also means you’re pulling against an equal and opposite force directed down into the bench. Which is structural, what you’re ‘attached’ to, and therefore something to pull against. The vertical component like pulling a peg out of the ground, and like the rowing machine. This vertical component you also counter with your legs of course (mostly). So again, yes a very important thing to be able to do. Makes me wonder how functional an angled setup on the out-feed table would be? So that you could direct more of the force down into the floor and have something to pull against. Standing this time of course.

So one could still apply all the forces at the Giraffe as at the Horse. However there may be a special consideration at the Giraffe. Yes you’re attached to it where you sit, and yes you can still pull against those strong-as-a-horse legs. But now what you’re pushing against with your legs isn’t attached any more. Not vertically at least. And the vertical component of the pull stroke that’s created by the wedge platform isn’t countered within the structure and system of the bench. So you’d be pulling the bench upward with the work piece. Now if you were standing above the Giraffe pulling upward on the pivoting design i’d say this would be a problem. But you wouldn’t be. You’d be pulling mostly toward yourself with some component of the force acting upward. And at the same time all the weight of yourself and the bench countering that partial upward force.

The other thing that makes me think that the giraffe won’t fold upward is what happens when you push against the ground when seated as you would be at the bench. Try sitting on a chair or stool with legs not folded beneath it, and push with your legs. What it causes is rotation (tendancy to roll or fall backward), not lift. And you’d turn that into pulling stroke force. It will be more demanding than the Horse on frictional forces at the seat and at your feet on the ground. But I don’t predict problematically so.
So I don’t think that having no foot peg to ‘row’ against will be a major problem.

Important to note though, is that this all has to do with pulling action such as using a spoke shave at the Giraffe. Tasks where you just need the piece clamped in place wouldn’t suffer from having no foot peg to push against even if i were wrong about the above.

Thanks JJohnston, that’s exactly the type of thing i need help thinking of. I hadn’t given it that much thought, and you worried me for a minute. :)

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