How to make a sphere

[feinddj]

Does anyone have a method for making a beach ball type sphere? I have found some templates online but want to actually know the math or method.

Thanks,

David

[Burkhardt]

What size? Just a sphere or with some pattern? With or without rotary axis?

[feinddj]

I need the unwrapped sphere. As if you were making a beach ball with 6 panels. The actual piece is to be 6 feet in diameter

[Burkhardt]

Ah...sorry if I just don't get what you want to do but each of these panels would still be 3-dimensional. While you can unwrap a cylinder or a cone on a flat surface you can not unwrap a sphere or ellipsoid. The best you could do is segment the surface into a faceted polyhedron. I have been working a bit on such tools lately (http://www.talkshopbot.com/forum/showthread.php?22163-Polyhedra) but I don't know if that is what you need.

[feinddj]

As in many things, you have to know what to search on in order to find the answer. I was looking for a GORE CURVE, most commonly found on pages about globes or parachutes. The method I ended up using (and using Aspire) is to draw a rectangle, width is the circumference of the sphere, the height is one half the circumference. Draw a line as an equator across the length of the rectangle. Divide it into as many sections as you want, the more sections, the more it will resemble a sphere when put together. I used the copy object along vectors tool to space 7 circles along the line for six spaces. Divide the space in half top to bottom. Use the three point curve tool to draw from the midpoint of the section top to the edge of the rectangle. Mirror across while making copies and you should end up with 6 pointed footballs. here is the site that explained it the best http://octopus.gma.org/surfing/imaging/globe.html

[Burkhardt]

That would work if you use thin flexible plywood or other sheet that can be bent. Is that the plan?

[feinddj]

Not my plan, but it's the clients plan. If I'm feeling nice I may offer to drill holes so they can sew up the ply. They are going to use bending poplar.

[bleeth]

The problem with bending (or any) ply is it only bends in one direction. Designs of curved panels to be built from plywood need to take that into account. In boat building hull designs made for plywood take this into account and are called "developable". When the pieces are bent in the polar direction they won't bend equatorially. They can have a go at it but if I were you I would take responsibility for cutting parts only with no guarantee of success in construction. The edges of the ply where the sections come together also will vary from 90 degrees as they go from the equator to the poles. That's why they use steamed wood for barrel making. They have to deform the staves to get the curve.

[wmwmacs]

Hi David

"but want to actually know the math or method. "

I have a sheet metal background and have used several methods to develop a Sphere pattern. his is one.


http://www.talkshopbot.com/forum/attachment.php?attachmentid=27050&stc=1

[wmwmacs]

Looks like i need help posting this.
not sure why the math page is not posting,

[feinddj]

I have that as well, in a book called Circular Work For Cabinetry and Joinery. Its from about 1900 and I think its available on the web. Its the one shop book I keep having to replace as people borrow it and then neglect to return it. The method that I described would resemble an orange peel after you slice it. It will have facets but its not my issue, it's the clients request.

David

[wmwmacs]

Ball Development by gores.
1900 s ? I will admit to the 1940 S.

http://www.talkshopbot.com/forum/attachment.php?attachmentid=27087&stc=1

[Antti]

Sorry about the late answer - not sure if you got it figured out yet :)

Anyhow you have to calculate the zone pattern in steps (height and width). See example image, there is the math to calculate beach ball type zone pattern dimensions. I can send you an excel sheet with example formulas and graph, if you need.

Regards,
Antti

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