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Shaving Giraffe - a shave horse re-design from Africa

by RobynHoodridge
posted 447 days ago


21 replies so far

View MattADK's profile

MattADK

20 posts in 891 days


#1 posted 447 days ago

Very cool!

-- Matt

View Rick M.'s profile

Rick M.

3384 posts in 882 days


#2 posted 447 days ago

This is interesting but I suggest making a life size version along with a traditional shaving horse and actually trying them out.

-- |Statistics show that 100% of people bitten by a snake were close to it.|

View woodsmithshop's profile

woodsmithshop

1085 posts in 2048 days


#3 posted 447 days ago

you will have to stand up to change your clamping position

-- Smitty!!!

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RobynHoodridge

126 posts in 832 days


#4 posted 446 days ago

Woodsmithshop, you’ve brought up what i think is the biggest thing to address.
You may not need to stand up completely. Just take up your body weight with your legs. I agree this could be too much to ask the user to repeat for very long.
But that’s for a version of the design concept where one’s weight is (the seat is) far forward of where the rear support holds up the Giraffe. How about if we move that forward to be directly under, or nearly under the seating position. Maybe even resting on a see-saw point – something much like a saw horse with an apex. Then a slight shift of ones weight backward (rolling on ones bum, so no standing up required) would release any clamping force. Maybe even counter the clamping that’s a result of the mass of the Giraffe?

-- Never is longer than forever.

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RobynHoodridge

126 posts in 832 days


#5 posted 446 days ago

What i’ve thought about the release of the clamping action so far is that it might be functional to have handles on the end of the swing arm that clamps down. These are used to push up and out against, and counter the clamping force to open the vise. Especially if the ratio of the swing arm sides is around 1:1 this action should be quite easy. More so if you’re not lifting your own weight because of the positioning of the rear ‘legs’ as i suggest above.
This way the clamping action is ‘on’ most of the time (automatic state) and ‘off’ only when it needs to be, when changing orientation of the work piece.
There is another way. I hesitate to even mention it because i like how simple the Giraffe could be. But there could also be included a foot operated lever to lift the bench up and release the clamping force. Maybe a part of the bench, or maybe a separate device. Think of those old manual operated railway platforms with the dual pump up and down action cantilever to make them go. You stand on one side and the other pushes up on the bottom of the Giraffe.
I prefer the first ideas though. But as Rick M. says, i may need to have it in full scale to test that.

-- Never is longer than forever.

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woodsmithshop

1085 posts in 2048 days


#6 posted 446 days ago

as far as the raising up of ones body even a small amount would get tiresome, especially, even though I am only 21, my knees are 70, and they would not like very much of that.
I realize you are trying to develop a more efficient method, and I appreciate that you are innovative.
but I think if your efforts were to be used to come up with a higher leverage method in the existing shaving horse design, then it would not take so much downward pressure with the legs to clamp stock. the existing design has proven over many years to be very efficient. maybe just an improvement on the clamping force. I have watched Roy Underhill work on a shaving horse many times and he changes the position of his work quite often, and standing or rolling back would result in lost time, imo , he seems to be able to change stock position quickly almost without losing a stroke.

-- Smitty!!!

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RobynHoodridge

126 posts in 832 days


#7 posted 446 days ago

You’re right, i wouldn’t want to be continually doing squats.
Does he change the position of the work for every type of activity at the shaving horse? Or might the horse suit one type of activity and the giraffe another? Like holding down something that’s being chiseled or carved from only one side.
But i still think there’s a way to make the giraffe cycle quickly through clamping.
I’m not trying to replace the horse. I think we’ll be better off also contemplating other options. Which might be better for certain things.

There is a much better lever system than just a straight leg for the more typical shave horse style bench. Have a look at what Bob Slade has done here – http://www.forestofavonproducts.co.uk/news/stanford-shave-horse
I mean besides the standing aspect of it. Which i think is great, but isn’t what i want to point to. The ‘triangular’ extension of where the foot ‘pedal’ is should let you use your weight rather than muscles, and should rotate the force around and over the work piece better. Also allows a longer lever for greater force.

-- Never is longer than forever.

View Rick M.'s profile

Rick M.

3384 posts in 882 days


#8 posted 446 days ago

It seems like you are trying to improve something you haven’t used. The German dumbhead has been around for centuries with very little modification and for good reason; the English style is a tad newer but works on the same principle. That’s why I suggested you make working models and actually use them. Awhile back two prominent woodworking authors set out to modernize the shaving horse, unfortunately I can’t find the video at the moment, and what they came up with was pretty cool but very complicated and in the end I didn’t see that it worked any better. Don’t get me wrong, I’m not trying to dissuade you just encouraging you to build and use the horses so that you know what works and what doesn’t.

-- |Statistics show that 100% of people bitten by a snake were close to it.|

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RobynHoodridge

126 posts in 832 days


#9 posted 446 days ago

Thanks Rick. No, i get it. Don’t worry. And you’re right of course i should build it. Them. Many iterations.
But i can’t. Not right now.

Different folks have different approaches to product design. I can usually see a lot of what’s going on even before the thing’s built. (what works and what won’t) And so work through a lot of changes before anything’s spent on prototypes. For now i’m looking for help on just this. The concept. I know they’re maybes. But that’s how i like to work – dealing with all the maybes first. Someone working a different way, like those prominent woodworking authors you mention say, might create something quite different just because of difference in that approach. Complicating it for instance.
Also, because i’m not developing a product for my own gain (not selling them and won’t own the intellectual property), I’m not going to do all the development through to perfect before i tell the world about it.
And thinking of ALL the possible versions is something i want to promote too. Shelling out a finished product that we don’t have to have considered possibilities on would leave something that people either take up or don’t. Instead of something like “Hey, that version sucks because of X, but if i replaced that with Y it’d be great.”

So i know i should build it. But not yet. And i will definately report findings when i do.

-- Never is longer than forever.

View JJohnston's profile

JJohnston

1572 posts in 1794 days


#10 posted 445 days ago

I’m skeptical. I think you need to push/brace with your legs, for the equilibrium, whether or not the leg force is being used to clamp the piece. I don’t think you’re right with the assertion that bracing with your legs will unsettle your sitting position; just the opposite. Think of doing seated rows with the rope & pulley at the gym. You have to have your feet up against the machine. I don’t have a horse, but I’ve tried some shaving work with a piece clamped to the outfeed table of my jointer. It was nearly impossible, because I couldn’t brace myself.

-- The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by menacing it with an endless series of hobgoblins, all of them imaginary. - H.L. Mencken

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RobynHoodridge

126 posts in 832 days


#11 posted 445 days ago

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. :)

-- Never is longer than forever.

View mafe's profile

mafe

9241 posts in 1592 days


#12 posted 445 days ago

Hi ho,
First thank you for asking my oppinion, it makes me happy knowing I’m not all hopeless. Smiles.

I am not sure that I understand it completely, but if I do so; the giraffe is loaded with a pice of wood and the weight of the body holds it in place – brilliant thinking!

But…
Using one of these shaving horses you usually turn the item you work on rapidly and on going, it is not a static tool – is this possible while sitting down?
How do you release? By lifting the Giraffe?
Why don’t you make a foldable leg in the back? It will make it useable in all situations and a stand alone tool.

I am impressed and love that you question the horse, this is where invention gets educated.
Kepp up the ideas.

Good hunting.
Mads

-- Mad F, the fanatical rhykenologist and vintage architect. Democraticwoodworking.

View RobynHoodridge's profile

RobynHoodridge

126 posts in 832 days


#13 posted 444 days ago

Hi Mads
Thanks for taking the time.

Yes, you’ve understood the concept.
The thing about using the body weight to cause the clamping is that the standard state is with the jaws clamping the work. Good for tasks that need long sessions of the clamped state, but probably not good for drawknife work.
You asked if it’s possible to turn the work while sitting. Well, not in the most basic form of the design. There are ways to make it possible. None i’ve thought of make it as easy as it is with a shaving horse. Here’s one idea for making it possible-

The handle (or some other version of handles) in blue give you something to push on to forcibly open the clamp with your upper body against all force of the clamping action. Not something you really want to be doing much of. A foot actuated lever below the bench could also be developed for lifting the bench and therefore un-clamping. And here leg action would UN-clamp the work.

Yes, to remove clamping force you would have to remove force down on the bench. I think that a balance could be found by tweaking the design so that the weight of the bench only causes a light enough clamping that the work could still be manipulated, but when sitting on it that force is much greater.
I’ve also thought of a spring to counteract only the clamping that’s due to the bench weight. But all of these things are complications.

So all round, it’s not going to be a natural thing for the giraffe design to clamp and un-clamp repeatedly.

The idea of a fold-away leg at the rear is great. Thanks.

Cheers

-- Never is longer than forever.

View rance's profile

rance

4106 posts in 1663 days


#14 posted 444 days ago

Robyn, There are parts I like and some I don’t. As already mentioned, Sitting to apply pressure could be a problem. However, if you put the rear support right where you sit, then you can somewhat rock forward & back to adjust the pressure. In the end though, I’ll bet you’ll get too much pressure and it will be difficult/tiresome to rotate the workpiece.

See if you can find a video of someone using one of the styles of horses. You’ll see that there is quite often a release of pressure to rotate or move the piece.

I really like that you are building it to be collapsable. I think that is a key feature.

Keep tweeking. I’ll second the suggestion to build one as a prototype. Use 2×4’s which can be gotten for free. You’ll get as much feedback with using it as with just questions. Remember that in designing, you’ll have to do revisions. Press on(pun intended).

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

View mafe's profile

mafe

9241 posts in 1592 days


#15 posted 444 days ago

A spring perhaps? So when you lift the jaw opens…

-- Mad F, the fanatical rhykenologist and vintage architect. Democraticwoodworking.

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RobynHoodridge

126 posts in 832 days


#16 posted 444 days ago

For opening the jaws
There may be folks who are happy with standing up each time. In which case they could devise a spring action to open up the giraffe as they do. But i personally wouldn’t want that. So here’s my best idea ->

What the shaving horse has got right about it is that the (free) legs are used in determining the clamping. However there’s nothing to say that just because we’re swapping from “usually open” to “usually clamped” we can’t keep with the switching between them by leg action. Here are pics of the way i modified my model giraffe to be activated using ones legs.


non-stretching (cable) line between the giraffe bench parts, with a pivoting arm that depresses it.


With the leg operated arm depressed, the distance between ends of the giraffe is forcibly shortened, and the vise is un-clamped.

This should have just as much usability as the shave horse. I mean, it’s functionally the same thing : a leg action determines whether the work is clamped in place or not. So those worried about turning the work piece often, and potentially having to get up off the bench to do so, you can see that there are ways to not have to do this.

I would choose to use steel rope for the line. It could have ‘loops’ at various lengths along it for different positions of the swing arm (in a version that has an adjustable arm). And it would just hook in place (and come off again as easily) when the fold up giraffe goes to and from its pen.

What i don’t like about this is that it’s not as simple as the original, where there were just two major parts that pivot on eachother. Don’t get me wrong, it’s no big deal i think. I just loved the pure simplicity of a version with no un-clamping mechanism. Now we’re introducing another pivot. And we’re back to having something under the bench that could jam against things on the floor etc..
One thing though, is that we’re NOT back to the legs having to be used while you’re working on the piece. Which i like the sound of.

-- Never is longer than forever.

View GEOwen's profile

GEOwen

7 posts in 439 days


#17 posted 435 days ago

@Mafe:

No need for a spring to cause the jaw to open any appreciable distance when pressure is released because all you need is for the jaw to relax so that you’re free to move the workpiece around to whatever position you want for the next few pulls on your drawknife/ spokeshave.

Your mentioning a spring did give me an idea….

The purpose of the jaw is to clamp the workpiece so that it doesn’t move when you work on it. With a reasonably sharp drawknife, you’re probably not pulling with more than 20 or 30 pounds of force unless you’re trying to take off a lot of wood with each stroke. No matter what you’re doing, unless you’ve spent a lot of time in the gym your arm muscles aren’t strong enough to apply enough force to break the grip resulting from your entire body weight So, my idea is to let the seat be a separate item supported by a spring on either side with those springs going all the way down to the ground. Those springs are stiff enough to flex only a few inches under your body weight. During those last few inches of travel, the seat compresses a single weaker spring (or maybe a piece of foam rubber?) that transfers weight to the lever action of the giraffe so that maybe 50 or 60 pounds of pressure is applied to the clamp.

Might give some of the seating comfort of having an office chair mounted and would be easier on the knees by automatically reducing the effort needed to relax the clamping action.

-- “The American Republic will endure until the day Congress discovers that it can bribe the public with the public's money.” ― Alexis de Tocqueville

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RobynHoodridge

126 posts in 832 days


#18 posted 434 days ago

Hi everybody. I’ve made a full scale version. If you’d like to have a look, here’s a link to my LumberJocks blog entry about it: http://lumberjocks.com/RobynHoodridge/blog/34452

@GEOwen: Now you’re really thinking! I love it.
You’re right about not needing a tonne of clamping pressure. However…. Having made one, i can tell you that the clamping pressure isn’t immense the way you might fear. The user’s body weight is far back, towards the legs or whatever rear support there is. This rear support point is actually acting as a pivot point for applying the force of teh weight, so we can speak about it as torque. And from what we know about torque, the length ot the lever is important. So a seating position far back lessens the effect of a full body weight on the bench. The angle of the swing-arm also reduces the force applied. Let’s say it’s at 30 degrees – then we’re already at only 2/3 of the full downward force being converted into clamping pressure.
Your sprung seating idea sounds like so many of mine – perfect for some ultimate version of the Giraffe, but probably not something that folks will do. Of course one could take the Giraffe’s principle in any direction, but the way i’ve gone with it is the most simple. Sourcing springs takes it quite a leap from simply some rafters, pipe, board, cable and castors. With the right foot operated lever acting on a cable under the bench as in my firstborn, it’s also not difficult to open the jaws against the forces created by weight.
At the moment i’m crazy about suspending things. My desk is suspended from the ceiling, so no legs beneath the tabletop to bump into etc.. And i’m now imagining at least one end of the Giraffe strung up on cables from the roof. And perhaps with springs involved to ‘dampen’ harsh seating etc. :)

-- Never is longer than forever.

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RobynHoodridge

126 posts in 832 days


#19 posted 434 days ago

The question of clamping force got me wondering about the actual value. So i did the very scientific bathroom scale test.
The weight of the Giraffe itself creates about 7 kg (15.5 lb) of force at the clamp.
With me seated on it, the force ranges roughly between 15 kg (33 lb) and 19 kg (42 lb). Depending heavily on how far forward / backward on the seat i place myself. And i weigh 70 kg (154 lb).
Moving the position of the clamping bar (top vise jaw) backward by 50 mm gives 4 or 5 lb greater clamping force.
You could work out pressure values from this (pounds per square inch for example), which would obviously depend on the size of what you were clamping.

-- Never is longer than forever.

View Mathias's profile

Mathias

1 post in 272 days


#20 posted 272 days ago

Hi RobynHoodridge,

I have been admiring your take on the classic shaving horse, as I am trying to design one myself. Being new on this site, I have not been able to send you a message. So instead I address you here in the comment section.

A picture of the model you made, doing a yoga pose, came so close to the final design I myself had thought of, that I was hoping you could help me figuring out if it is even possible making a ‘shaving dog’, which would work.

My problem is, that when shaving or peeling larger objects, I find it necessary to stand beside the object, using my thigh muscles, to do the heavier work. This is something which is impossible to do if I have to use my feet pinning the object to the bench, or my whole body, as you do.
By looking at your model bench, doing yoga, it seems that it is the object locked between the two joints, keeping the whole thing from collapsing, but using gravity to pin down the object. And therefore leaving you to stand beside the bench for optimal working conditions.
It would off course be necessary to leave out the seat, and have a bigger angle between the ‘legs’, for optimal stability, though.

Since you are the only one, seemingly coming close to the same solution, do you think it would work?

If so, I would much appreciate your help.

Thanks,
Mathias

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RobynHoodridge

126 posts in 832 days


#21 posted 271 days ago

Hi Mathias

Since you’ve signed up now you should be able to send messages. But it’s also great to carry on the discussion here for all to see the toughts.

My first impression of what you want to do is that your hard work (thigh muscles used to leverage body mass) and large forces are not appropriate for the shaving bench. Woodworkers do a lot to get a sturdy, very heavy workbench to push on as you’re describing. Especially for lateral (horizontal) forces like planing. And then vises will do the clamping that you’d want.
I think you’d need a massive (heavy) shaving giraffe in order for it’s own weight to exert enough clamping force. Or, some clamping mechanism like adding weights, incorporated springs, or – a vise. In which case we’re back to it being best to use a workbench.

Have you seen the type of workpiece holder that props up against a wall etc and is nearly vertical? So you use it standing and pull downward with the blade?

Is the “shaving dog” something specific?

Just also want to check whether you’ve seen my blog post on the full scale version of the giraffe that i made.
http://lumberjocks.com/RobynHoodridge/blog/34452

-- Never is longer than forever.


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