Interesting problem...

[geneb]

I have an interesting problem I'm hoping you bright folks can help me with.

I've got a spherical-section shape:
http://www.diy-cockpits.org/pdf/test_part.pdf that I need to turn into a flat pattern in order to cut it out from mylar film on my 'bot.

I have a method of re-joining the seams that would result from the flattening process, but I don't have any software that can perform the flattening itself.

Any suggestions as to something that could do this?

Thanks all!

g.

[Brady Watson]

You can try to 'Unroll Developable Srf' in Rhino.

You can also try Pepakura Designer (http://www.tamasoft.co.jp/pepakura-en/)

-B

[geneb]

Brady, do you know if that feature is in Rhino v3? That's the edition I have - I'll have to get it re-installed.

tnx.

g.

[hespj]

I think Rhino 3 has limited ability to flatten non developable shapes.

"Smash - is a special version of UnRollSrf that does not check to see if the surface is developable. It is not recommended now that Squish is available."

http://wiki.mcneel.com/labs/advancedflattening


"Smash - Flattens a surface as you might expect from the command name."

http://www.rhino3d.com/3/bonus.htm


I think you have to download the bonus tools on that page.

Send me the file otherwise. I'll flatten it in Rhino 4.

John

[changrudy]

If you have a 3D model or some accurate dimensions of the sphere, I can do it for you. I use autodesk inventor that can flatten the piece.

Rudy

[wmwmacs]

Gene

If I may introduce myself I am a retired sheet metal contractor. I would consider this a compound curve and lay it out with Gores. If you like I can sent you some info on developing this type of pattern.
Bill

[Mayo]

I have a similar issue with a file in Google SketchUp. I'm trying to flatten a cylindrical object. I found some scripts that are supposed to flatten.
If you can use SketchUp, they might work for you.
So far I've only been able to get it to break apart into pieces rather than one long uncurled shape.

One is called Flattery, another is called Flatten, and another is called Unfold Tool.

I don't have enough experience with SketchUp yet to comment on these scripts.

[geneb]

Thanks for the ideas guys!

Inventor can't unfold a surface that has curves in more than a single axis - at least Inventor 2009 can't, even with the sheet metal module. :)

It turns out that using "gores" is going to do the trick!
Here's some info and a couple of calculators for creating them:
http://www.cit.griffith.edu.au/~anthony/kites/parafauna/chute_design/#calc (http://www.cit.griffith.edu.au/%7Eanthony/kites/parafauna/chute_design/#calc)

I'm going to create a gore pattern in AutoCAD and use my PRT Alpha to cut a few of them out from 1 mil mylar. The vinyl cutting bit I bought (can't recall the vendor at the moment, but he also sells the diamond drag bit and the pen holder bit) should work quite well for this task.

Thanks to all that replied! When I get a proof of concept model built, I'll post pictures in a new thread on the Virtual Show & Tell board.

g.

[changrudy]

Gene,

I guess inv2010 has this new function called contour roll that can flatten your piece. See pics of the flat pattern.

Give me the dims and I can do it for ya,

Rudy

[geneb]

That's pretty slick Rudy!

Do you know if that contour roll function assumes any stretch on the material?

My test shape is a 48" radius with a 40 degree vertical arc. I'm going to build a 60 degree wide section of that radius. The end result will be a spherical-section mirror.

Thanks!

g.

[changrudy]

Gene,

Your flat pattern dimension is 49.312" x 33.547". I assumed the rotation axis is the same as the 48" radius (it could be different).

The default k-factor is .44 which calculates the stretch. But this is normally for a metal sheet metal fabrication which has different bend modulus (stretch) than mylar but it should be close enough.

And it was my pleasure, many ppl on this forum has helped me out before!

Rudy

[geneb]

Thanks Rudy. I've got to get my copy of Inventor upgraded.

The only problem I have with a monolithic sheet is I wouldn't be able to cut the whole thing on a 'bot - I need to find a roller-based vinyl cutter. The sheet for the 180 degree mirror would have to cover a 150"+ arc length.

g.

[kenz]

http://www.touchcad.com/