# developing true length on compound curve?

• posted
hi all,
Im trying to develop a shape thats a bit complex to me, for fabrication at
work. What we have is a large copper furnace, its a cylinder lying on its
side. The cylinder is about 20 feet in diameter. I have to build a mouth
to sit on top of it, you could imagine the mouth as being a second piece of
pipe, meeting the cyllinder at a 90degree angle. The mouth itself is
actually a shape with two straight sides (parallel to the ends of the
cyllinder) and two curved sides running parallel to the cyllinder, each
curved side with a different radius.
Ive drawn out the cyllinder and the mouth, in plan and in section and the
results are showing me what i want, but its not really what i want. The
purpose of this drawing is to allow me to make dimensions for making the two
curved pieces. What i really want, is to be able to 'unroll' the curved
piece so its flat, then i can take dimensions off it at will. Imagine, more
simply if you like that im just joining two pipes together, and the second
pipe is joining into the middle of the first one. what i really want is to
be able to slit that second pipe down the middle and unroll it so its now a
piece of flat sheet. any clues how to do this? Im sure there is something
simple i can do here that im missing.
the alternative, is looking at the overhead view, taking lines every foot or
so and drawing them out onto the front and side views then taking individual
measurements.... but this really only gives me true lengths while the piece
is *curved*. Which means the sheet will need to be rolled first, then
measurements projected onto it from a hypotehtical flat line, then the
ellipse drawn, then cut. In an ideal world i would be able to calculate
that ellipse first, mark it out onto a flat sheet, cut it, then put it
through a roller and it would all fit up nicely. The sheet of steel is
about 2" thick which is why it would be easier to cut ot before rolling.
Any and all advice welcome!
Shaun
Australia
• posted
You need something like:

• posted
A while back I used a free utility called unwrap that, although crude, did work for this kind of thing. Maybe it's still out there somewhere.
• posted
"Shaun Van Poecke" a écrit dans le message de news: 7SpWh.17445\$ snipped-for-privacy@news-server.bigpond.net.au...
Here's a page taken from a technical manual explaining how to do the basics. It's in french, but I'm sure you can figure it out from the graphics.
BTW, I've never tried to post a link from there, so it might not work. I'll check back to see how it turns out.
Dr Fleau
• posted
"Dr Fleau" a écrit dans le message de news: 0P5Xh.15408\$VF5.10388@edtnps82...
Ok. Need to register to Box.net for it to work. Sorry. I'll try to figure something out.
Dr Fleau
• posted
"Dr Fleau" a écrit dans le message de news: 0P5Xh.15408\$VF5.10388@edtnps82...
Take 2