On Sat, 08 Nov 2003 15:40:14 GMT, Larry Jaques wrote:
On Sat, 08 Nov 2003 02:21:57 -0500, Gary Coffman
brought forth from the murky depths:
On Thu, 06 Nov 2003 18:28:30 GMT, Larry Jaques wrote:
What won't work?

What won't work is trying to stretch a diameter
around half a circumference. In other words, the

I picked up on that this morning when replying to
John. Thanks.

You're welcome. It should be obvious that what you
really have to do to project a 2D figure onto a 3D
surface. What may not be so obvious is that wrapping
the 2D figure around it won't do that, because the
projected figure on the pipe surface is an ellipse,
not a circle.

The easiest way to generate the correct figure is to
hold the 2D template *flat* above the pipe, and drop
perpendiculars down to the pipe surface to form the
required curve. (A stiff template and a long marking
pen will do for the precision needed for welded joints.)

BTW, the flat projection method will also correctly
describe the elliptical mating hole you need to cut
in the other pipe.

Gary