Skeleton Sphere Chair

[Burkhardt]

This is a continuation of the Polyhedra software project thread that I posted a few weeks ago. I realized that this tool can be used not only for the usual polyhedra shapes but also to carve any polygon board shape with any desired edge miter angle. As a proof of concept I started working on a 60's style hemisphere chair with a skeleton frame. This is the idea in CAD:

https://lh3.googleusercontent.com/-yXWVGCkdt_U/VmZWoTV-68I/AAAAAAAAGC4/yQt2qc_oZjA/w477-h519-no/BuckyChairCAD.jpg

It is made from 54 pieces of 8" long 2x4 redwood studs:
https://lh4.googleusercontent.com/-QJ6pII6JVFA/VmZZgmS9DzI/AAAAAAAAGDQ/4Ycztp6plZM/w800-h534-no/1-DSC00175.JPG

Custom vacuum pod for reproducible placement:
https://lh4.googleusercontent.com/-aMusl0NU1-A/VmZZhGso2VI/AAAAAAAAGDY/eE3hUqtRczA/w800-h534-no/2-DSC00176.JPG

One of the 36 hexagon/pentagon edge elements after drilling and miter carving with a ballend bit (there are also 18 hexagon/hexagon edge elements):
https://lh4.googleusercontent.com/-ktr-swSGI-A/VmZZhf4czhI/AAAAAAAAGDg/2UWbun5ayZA/w800-h534-no/3-DSC00179.JPG

To be continued...

[Burkhardt]

More pictures of current progress:

Pentagon elements glued together:
https://lh4.googleusercontent.com/-61uX80ftG_4/VmZZiBcMXwI/AAAAAAAAGDw/icil3DVdgKY/w800-h534-no/5-DSC00182.JPG

First temporary assembly, using cable ties to prove the miter fit:
https://lh5.googleusercontent.com/-zT9MaGCBzPE/VmZWnkUjeHI/AAAAAAAAGC0/6RWTc_eZ3JE/w858-h835-no/DSC00186.JPG

Next will be gluing all remaining joints, attaching the legs, sanding everything, danish oil, "sewing" the joints and stringing the skeleton openings...looking good so far. Not sure though if big enough for me with modest 5'10" . And, after a test sitting in the frame, I needed help to get out. Oh, well :)

[myxpykalix]

I would have loved to see a picture of you struggling to get out...the shape reminded me of someone being hatched out of an eggshell. So i could see this being applied to like a dome shaped structure but as for something like a chair unless you carry your shape around to make the circle it would lose some of it's structural integrity?
It looks really cool to me. I like seeing some of the stuff you come up with.

[scottp55]

You need a BIG BAD cushion in there G:)
Or maybe an Irish Wolfhounds doggie bed.
Or maybe some Hatteras hammock material?
Looking good!
Be nice if it could be suspended.
scott

[Burkhardt]

You need a BIG BAD cushion in there G:)
Or maybe an Irish Wolfhounds doggie bed.
Or maybe some Hatteras hammock material?
Looking good!
Be nice if it could be suspended.
scott

It would be possible to hang as a hammock chair since the structure is really rigid but I don't have a covered porch or similar so I will attach 3 legs. The cushion should not be a problem, since you can buy special cushions for sphere or shell chairs.

[Brian Harnett]

Thats a cool chair I like it.

[knight_toolworks]

How are the angles cut? is it a 3d cut or what? everytime I have close to 90 on a 3d file it is really rough.

[Burkhardt]

How are the angles cut? is it a 3d cut or what? everytime I have close to 90 on a 3d file it is really rough.
It is kind of a 3d-cut, but not generated with the usual CAM tools. I made a special software application that cuts a single spiral tool path around all board sides with a ball end bit from top to bottom (plus roughing, if needed). In a way it is like the waterline toolpath strategy that the Deskproto CAM software does. However, it is not based on an .stl file. It only needs the board corner point positions, the thickness and the miter angles of each edge.

The stepover (distance between subsequent spiral windings) is calculated from the specified allowed surface ripple that the ball end creates. E.g. in case of this chair project, I specified 8/1000" ripple which results in approx 1/10" tool path distance with a 1/4" bit. Cutting a single board this way takes about 6 minutes @ 3.5ips. The whole lot of 54 took a good Saturday afternoon. The cut can be made smoother but that will of course take longer to machine and 8/1000" ripple on the exposed sides is easy to sand away. On the glue joints it is even helpful for joint strength.

The cut surface is very smooth, only on the end grain there is very minor tear-out of the brittle material between the harder growth rings. But that is almost unavoidable with such kind of softwood. I still need to cut the legs and will take a close-up of the surface.

[Burkhardt]

O.K., here are the close-up pics. Please keep in mind this is ConCom Redwood, not exactly the best carving material...The cut is made in "conventional" direction but I noticed not much difference to climb cut, only the effect of 45 degrees and 135 degrees to the grain are reversed, see below.

Along the grain the cut with the ballend mill bit is really smooth in both directions, except where some knots cause an off grain pattern:
https://lh5.googleusercontent.com/-emOc-UYpEDE/VmufjW7YnsI/AAAAAAAAGFg/TenAfjEbM7o/w1024-h806-no/4-DSC00196.JPG

45 degrees (more along the grain):
https://lh5.googleusercontent.com/-QUziwDC5BFI/Vmufel_BRYI/AAAAAAAAGFM/jazfPiJV2Pc/w1024-h783-no/1-DSC00191.JPG

135 degrees (more against the grain):
https://lh5.googleusercontent.com/-s_hlWjnCeOM/VmuffNyiK0I/AAAAAAAAGFQ/lIMomgwTMpI/w1024-h772-no/2-DSC00192.JPG

90 degree end grain cut (notice the difference between the hard, dark growth rings and the brittle wood in between):
https://lh6.googleusercontent.com/-JuIucvdIFZg/Vmufi7XtQ4I/AAAAAAAAGFc/iT1mpNowYwQ/w1024-h700-no/3-DSC00195.JPG

Overall, it is more than smooth enough for my purpose. The ripple created by the ball end bit with the given path offset is way bigger than the roughness/tearout by the bit.

[Ajcoholic]

Thats pretty wild! You never fail to come up with some very interesting stuff...

[Burkhardt]

Thats pretty wild!... Thanks, I take this as a compliment :cool:

Some more work got done: glued all joints, sanded and finished with Teak Oil (I know not intended for Redwood but it works very well). Now I need to tie the joints because the butt-end glued studs are not strong enough by themselves, which is why I machined all the holes at the connections. I first thought of "sewing" with glue-saturated jute rope but found this still has too much flexibility. I guess I need some more experimentation but this is a proof-of-concept after all. Eventually this may become a handy gift for a child (once properly upholstered). It ended up a bit too small for an adult.
https://lh4.googleusercontent.com/-bxko_i2ctLs/VnDNOqZHP2I/AAAAAAAAGFw/55fdQDkOKOI/w723-h835-no/1-DSC00197.JPG

[scottp55]

Just wondering if perhaps canoe seat or snowshoe leather, done wet/allowed to dry/shrink, then shellac'd might work?
http://www.chichesterinc.com/SnowshoeWebbing.htm

[Burkhardt]

Just wondering if perhaps canoe seat or snowshoe leather, done wet/allowed to dry/shrink, then shellac'd might work?
http://www.chichesterinc.com/SnowshoeWebbing.htm

Scott, that would have been a good experiment. Did not think about rawhide and the tanned leather laces I have are too soft. Anyway, since this is only a feasibility project that I need to wrap up I ended up using nylon ties. The polygon openings were closed with strong duck canvas.
That is as far as I want to go now, I will give it away to somebody with small children and they can find an appropriate cushion or pillow.

https://lh5.googleusercontent.com/-9xnZwyo11I4/VpLMjvcPWQI/AAAAAAAAGG0/p3zf-Bwb7A0/w737-h835-no/DSC00293.JPG

https://lh5.googleusercontent.com/-nU5CxGBlruQ/VpLMkVDSaMI/AAAAAAAAGG8/gy6NpQLqdIQ/w850-h835-no/DSC00294.JPG

https://lh3.googleusercontent.com/-o4oCFDiD4gA/VpLMlBc3Y-I/AAAAAAAAGHA/9P_GZOmKiMM/w768-h835-no/DSC00298.JPG

[scottp55]

NICE G. !!
Funny, was just talking about you with another Fingermaker friend(Dan).
He asked me how I would go about making that "Match Box" that you made.
Quick answer was "I DUNNO"
Told him I'd play with it as soon as I get your programs onto this brand new laptop(Windows 10 and Hating it)
Keep making cool stuff:)
scott

[joe]

My wholehearted complements.

I'm glad to see your creative chair and appreciate the wonderful photography. This work is a labor of love. So thank you for sharing your talent with us.

[Joe Porter]

Those lucky kids will love that chair! They will probably fight over who gets to sit in it...I've already used "spell checker" three times just getting this far in my note, let alone design something like that...joe

[Burkhardt]

Thanks guys for the nice words! I will probably donate it to the elementary school library.
Yes, kind of labor of love but I really wanted to see if that idea I had in my head could be realized. Admittedly my wife suggested next time to design and build something we could actually use :)

[bleeth]

You mean like a dome shed or greenhouse in the back yard?
Wild Gazebo roof?
Shades of Buckminster Fuller!