Covering a glitterball

[fragged8]

Hiya peeps

So, I have been asked to make a fabric cover for a BIG glitterball 1m diameter. And seeing as I just installed a fabric cutting CNC machine I thought this would be the first cutting job.
The ball ( 1m diameter ) cover can have a large tolerance so it slips over the ball easily so i’m not looking for sub mm tolerance, it can be oversized by 20-30 mm. Also the half sphere part of the cover stops at the equator where I add a 250mm height skirt

I have tried unroll, flatten, squish and smash and get various results, My problem is the length of the segment I flatten is longer at the equator side than the skirt segment… As I know this I can just make the skirt segments longer but is there a better way to do this that is more accurate ?

Glitterball test.3dm (491.8 KB)

[pascal (Pascal Golay)]

Hello - you might try just making simple wedges if you have lots of leeway:

-Pascal

[fragged8]

Hi Pascal.

i’m trying to keep the sewing to a minimum, could I join the wedges to make quarters and still get a fairly accurate edge length when flattened to join to the skirt quarter ?
How did you make the wedges ?

[pascal (Pascal Golay)]

Hello - I guess it depends on the fabric, how low a number of panels you can get away with - if it is a bit stretchy, you have more leeway expand the panels - but you won’t be able to tell easily - the fewer the panels the more distortion you’ll have to accommodate. I guess you need the edge length of the lower edge of the straight quarter sphere panel to be no less that one quarter the circumference of the circle - and no doubt somewhat more. I am making stuff up, here, I don’t espacially know about how fabrics behave but:

See also the Squish command. It is not really designed to be used on such heavily curved surfaces as an eighth sphere but maybe useful…

-Pascal

[fragged8]

Hiya
thank you Pascal, man I wish I could afford for you to work for me heheh.

You’ve given me a few things to work with, yes the fabric does have a little stretch so I can make running adjustments. I was getting 20 to 30 mm difference in lengths which is too much but 5 to 10 mm would work for me.

I will cut cheap plastic sheet on the cnc cutter first and see how it fits together . .

Thank you

[jeremy5 (Jeremy)]

Hi @fragged8,

You might also want to try panelling each quadrant like this:

Should smash within 2.5% which ought to work with the stretch you have in your material. And you may be able to do without the six smaller triangles in the centre and still get an acceptable result.

Inspiration came from spinnaker sails. Worth looking into sail design for ideas.

Regards
Jeremy

[andrew.nowicki]

This is really a question about geometry. RhinoPolyhedra makes many shapes which approximate sphere. The best shapes are called geodesic grids - they are made of hexagons and pentagons. RhinoPolyhedra calls them dual geodesic icosahedra. Squish command (or expensive plugin called ExactFlat) can flatten spherical patches made by projecting the grids on the sphere.

RhinoPolyhedra (free plugin) is here: https://www.food4rhino.com/app/rhinopolyhedra
ExactFlat (expensive plugin) is here: https://wiki.mcneel.com/webinars/exactflat
This is RhinoPolyhedra screenshot:

[fragged8]

you’ll have to accommodate

awesome i like that it is elegant solution for what i do , with the added bonus I could make sails on my cnc cutter
So far I have made the sphere developable by rebuilding it like Pascal suggested but I will definitely spend a few hours working out how to do your solution because that too will help me when drawing full boat covers.
thank you

[fragged8]

hiya
I did toy with the idea of geo dome but the amount of sewing would be several times more than I wanted. But I will definitely get the tool because I have another project it may be handy for
I do know about Exactflat but the price is just crazy for me, i’m only a one man band so it would be hard to justify, although I would love to have it.

Thank you