Jeff Burks turned up an interesting patent for a camp stool that seems genius, and yet I’ve never seen an example in the wild.
Nathaniel Johnson of New York was granted patent 32,698 on July 2, 1861, for using a curious metallic (or wooden) orb as the centerpiece of a folding camp stool. In essence, Johnson calls for using an iron orb that is pierced by three rods as the folding mechanism for the stool.
In and of itself, using a sphere isn’t an improvement. But what Johnson shows is that each of the three legs of the stool has a sympathetic spherical recess. This small detail allows the legs to close tighter without significantly reducing the strength of the legs.
It’s a pretty smart idea.
The challenge, of course, is in implementing it. I’ll grant that a machinist of average intelligence could create the orb with the three threaded posts. But creating the spherical recess in the legs would be a trick with off-the rack tooling. I don’t know of many drill bits that have a spherical cutting surface. Some router bits do. But then you’d have to follow that tricky operation by drilling a perfectly placed hole for the rod of the hardware.
I can visualize a drill bit that would cut the hole and sphere in one go, but that bit doesn’t exist (as far as I know).
So this one gets filed in the “cool, someday” folder.
This has inflamed my lust to build some more campaign stools from the leather and wood scraps in my basement. And to dream of perfect spheres.
— Christopher Schwarz
I think this could be implemented pretty easily – on the small scale – with a simple drill press setup.
Position the leg piece to be drilled/milled properly on the drill press and clamp it down.
Using the 1/4 inch or appropriately sized bit, drill for the bolt.
Without moving the leg, insert a 1/4 inch shank cove (or other) router bit in the drill press, and mill the recess.
It’d be a pain, switching out the bits twice for each leg, and making a jig/fixture wouldn’t be all that tough, but for a trial run or just one or two stools, it may work out.
Brad
Nice. I tried something like that a while back and it just wasn’t durable enough… But then I found this: http://www.instructables.com/id/Multi-Function-Walking-Stick-Converts-into-a-Cha/ built one, used a big ring, and it’s pretty solid.
Just something to think about.
I agree there, the legs have their highest stress in the center (and the extremities), so avoiding weakening the center with a ring or replacing the rods by rings seems appropriate.
You could shape a spade bit easily enough to produce a spherical indent and almost probably enough of the point to drill the hole for the bolt also. Much cheaper than a router bit.
A machinist’s ball end mill has a hemispherical cutting surface. They are available from industrial suppliers and here is one example:
http://www.discount-tools.com/serall.cfm
The shank size may too large for a drill press but a lathe chuck could be used to spin it.
A conical socket would also mate with the ball.
What about a spoon bit?
I was thinking spoon bit as well. There are some big old ones out there with T handles all the way down to small ones for chair builders. If it isn’t quite a perfect sphere I would imagine a heavy scraper would clean it up. Scraper ground from an old file to just the right shape. Just a thought
Couldn’t you just use a curved gouge?
It would be easy enough to re-grind a spade bit to the shape you need. I think getting three holes into a steel ball for the middle would be a lot harder.
Many ways to skin this particular cat.
The big issue that I see has primarily to do with the difference between practice and theory. The ball and socket joint won’t remain as geometrically perfect, and therefore intellectually sexy, as we’d like to think. Wood moves. Not much, but it does. And perfect sphere to imperfect socket means uneven wear. That leads to slop. Not much, but enough. And then to more wear. Not much, but it’ll be there. And, iron rusts. Not much, but… In the end, it’s a pretty labor intensive solution to a really negligible problem. Cool idea. But
Less work, I think, to simply make a welded Y-shaped bolt, and live with the glorious imperfection of a straightforward design that’s good enough. And if you draw your 3 legs in cross section, at the Y joint, my guess is that they’ll prove to be pretty close.
To make this why not first make a hexagon rod all with equal sides, drill your posts in every other side. Chuck the rod in the lathe, turn the rod round, make the holes for the rods your center point, turn a ball of sorts, insert rods,
The legs, turn them onb the lathe, to DIA. = to “x”…. Next chuck them on the bench between a pair of dogs, use a round plane that best matches the dia. of the ball.
Best part is, it can be done with all hand tools and a treddle lathe!
Why does the indentation in the leg need to be spherical? Wouldn’t a counterbore of TBD1 diameter and TBD2 depth work? TBD’s determined by how deep you want to sink the ball in the leg.
I think the gallery have it Chris, bolt hole first then worry about the semi-sphere.
If I am reading the patent drawings correctly, there is a semi-spherical washer as well, between the wood and the sphere, which could be brass or some such ‘self-lubricating’ metal. That should stop the ‘iron’ sphere from corroding against the wood due to the hygroscopic action of the wood, the zinc in the brass washer being the sacrificial anode.
If you find or make a hemispherical cup, then it’s just a matter of drilling a hole with an auger or Forstner bit.
Hemispherical cup – http://www.lnasolutions.com/connection-solutions/detail/hemispherical-cups-and-washers-bv1-and-bu1
I have no idea of the availability of these or their cost, but they’d be pretty simple for a machinist to make. As long as they’re not too big, they probably wouldn’t weaken the leg too much.
Isaac
That’s pretty much what Roubo drew in the plate that inspired you to make one of your earlier versions of the camp stool.
There is a ball at the center of the joint in figure 8 of the engraving reproduced here https://blog.lostartpress.com/2013/02/21/this-stool-is-brown-waxy-a-bit-oily-and-sticky/
Ruobo’s fastener heads aren’t drawn right unless the pivoting happens at the ball, but otherwise the idea is pretty similar.
The easiest way to make the recess for the ball would be to drill the through hole first and follow with a rounded cutter patterned on a piloted counterbore. If the bit wasn’t piloted, pretty much the same thing could be accomplished drilling through and then dropping the leg onto a locating pin aligned with the rotating axis of a ball mill type cutter in a drill press. A combination of the two would be the most accurate.
Someone who took the time to patent was probably thinking production which would make the special tooling worthwhile.
Hip socket Reamer, I’ll see if the ortho reps will give me a small one to try out.
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For that time period my guess would be Johnson used a spoon bit or similar as others have suggested.
For modern woodworking bits Grizzly makes round-nose bits up to 1 1/2″ that likely could do the job for you using a plunge router and a jig to hold the blank securely.
http://www.grizzly.com/products/C1065
In theory you don’t, need much more than a dent.
I have an idea on how we can get these orbs made. It could be a fun project for the LAP community and everyone involved would win. Here is the idea….
My son is a machinist who programs and uses a CNC daily in a small job shop. I could get an estimate of how much it would cost me to have his shop make several orbs for me. If the price isn’t too high, I would respond back to this thread with the following offer. You provide an engineering drawing and shipping costs and you get one of the orbs in return.
Everyone could win in this scenario. You spend time making a drawing, pay shipping and get an orb in return. I pay for the machining and get to make several of the stools. My son works on a fun project and bring business to his employer.
Anyone interested in making the drawing?
“My son … bring[s] business to his employer.” Somehow I’m not seeing that aligning with your vision of everyone involved winning.
If you want to pursue the idea, print out the patent drawing and add some numbers for dimensions. Write 1″ or 0.25″ not 1.0000″ or 0.250000″ Be prepared to pay a lot more than you think to have some made.
Please help me understand who doesn’t win.
Agreed! If you guys end up making any, count me in to buy some.
If I’m making one or three of these for myself, I probably just handle the recess with a curved spoon knife and clean it up with a card scraper. And I would strongly consider skipping that last step. If anyone had a problem with the imperfectly mated joint, well, there’s always the ground.
If I’m making a lot of these, then the drill press + modified spade bit method mentioned earlier seems to be the way to go.
Drilling the sphere, however, does not sound fun.