# Back engineering

Discussion in 'How Do I...' started by Longshaor, Oct 27, 2011.

1. ### LongshaorMember

Hi all,

I've been doing other things for a while now, but a problem one of my best mates was having got me thinking about card modeling again and, try as I might, I can't wrap my head around this.

The item is a cone-shaped lamp shade. To my mind, a lamp shade is two circles of differing diameters separated by a vertical distance, so there must me some mathematical way to convert those circles into an arc to 'flatten' the cone from a 3D object to a 2D pattern. The problem is, try as I might, I can't figure this one out! Can anybody help me here?

Cheers & Thanks in advance!

3. ### ZathrosGuest

What you wish to do is construct a Frustrum. It can be frustrating. This link will show you how. You do not need to buy or download anything, a calculator does help.

http://www.analyzemath.com/Geometry/conical_frustum.html

These types of problems and their equations can be found on the link above.
4. ### LongshaorMember

YES!!!! I thought the frustrum had something to do with it. Thanks for the link!
5. ### RocketmanTanWell-Known Member

I've tried doing it the mathematical way, but I usually get lazy and just use Siatki. I try to make up for it by using the pythagoras theorem and pi for triangles and circles, though