Geometry question

Similar to the "How can I make a pattern to cut a metal pipe at 45 degrees?" thread answer by Randy Zimmerman.

wrote: (clip) I'm not going to specify diameter or pitch since I'm looking for a general method. ^^^^^^^^^^^^^^^ The general method is to make a working drawing. In the view showing the end of the round pipe, put in equally spaced radii. Project these into a side view, where you can see their length. Transfer each of these lengths, properly spaced onto a view of the "unrolled" pipe, and you will have a "development" of the piece you are looking for. It's a standard drafting procedure.

The method is general enough that the part the pipe fits to does not have to be a certain shape. It can be another pipe, any size, at some angle if you want, or even a sketched-in shape.

Divide the problem into two problems. How to lay out a cylinder that goes through the roof on one side of the peak. And how to do the same on the other side.

Dan snipped-for-privacy@lycos.com wrote:

The class in engineering school that I most hated was called "descriptive geometry".

Part of that course was learning how to graphically construct flat layout drawings of 3-dimensional objects, precisely what you are trying to do.

The required tools here a a texbook on "descriptive geometry" and a roll of grid paper, plus the time to read a chapter or two in the book. The methods are entirely graphical, and require no math.

Damn, how I hated that course. :-) Still, every 10 years or so I find something that I was taught in the course to be useful.

Harry C.

snipped-for-privacy@lycos.com wrote:

Evidently Leo took descriptive geometry too! :-)

Worse still, since he remembers the correct terminology, he likely teaches a course in the 'dreaded' descriptive geometry. :-)

Were I you, I'd pay very careful attention to anything the Leo tells you.

Harry C.

Leo Lichtman wrote:

For extra credit develop the end caps...

I'm sure the AutoCad weenies will demand equal time :)

The hole through a flat piece of flashing or one creased at an equal angle on both sides across the center of the pipe will be an ellipse with a simi-minor axis (r) of the pipe diameter and a simi-major axis of r/Cos(intercept angle).

If the angles are unequal you have to solve for both angles and lay it out as two half ellipses.

thread answer

Thank you Rick. I can use the example you gave and life should be fine. Descriptive geometry was one of those classes I wanted to take but at the time I drifted off to the world of computers.

Here is my first attempt to draw it:

Twenty years ago, I'd have done that with out asking anyone. When I saw Rick's link I was somewhat chagrined to find how much I have forgotten from when I took drafting.

Once I could 'see' the problem it wasn't too hard to make a spreadsheet to do the calculations either.

Thanks to all that replied to my question,

Wes S