is your math any better then mine???

[jackorocko]

I need some help, school failed me or it has just been so long that I have become stupid. Latter being the more likely. So please HELP!!!!!

I need to put in a chimney pipe, and I want to buy my chimney pipe. But I am having a hard time figuring out the length of the piece between the two elbows to get the pipe out past the overhang on my roof.

The overhang is 2 feet and and the elbow is a 'stiff' 30 degrees. Can not be changed. I have looked up the cosine, sine, tangent ratio table. http://portalsso.vansd.org/portal/p...6/TAB1792612/AA667DC74A36C5A8E0404A0A84004321

So now that I have my ratio's how can I figure out the two lengths, more importantly the adjacent and hypotenuse sides of the triangle? I think I am close, but that last bit of math formula is evading me. I will upload a picture soon in case my description is unclear.

 

[jackorocko]

Oh never mind, I think I got it.

Since I know the angle and the opposite side, then TOA formula is involved.

eg. tan 30 = 2/a
a = 2/tan 30
a = 3.46
3.46^2 * 2^2 = 16
sqrt(16) = 4

a = 3.46
o = 2
h = 4

Oh I remember now.

 

[poor mystic]

Yes, that's the way Jackorocko.
... and, you can always check your results using Pythagoras' Theorem. I just did, and the arithmetic looks OK to me.
If I were to leave trigonometry untouched for so long that I wasn't sure about stuff like that I would not be embarrassed to make an accurate drawing and measure the wanted side, which would help eliminate systematic errors.

 

[daddles]

Some simple trig is the way to figure that out; glad you figured out the method.

I'd like to comment on something that a lot of people seem to miss: make a scale drawing. When I worked as a scientist in industry before CAD existed, we had to design quite complicated systems -- and it was all done on paper with, basically, pencil, drafting scales, triangles, and perhaps a drafting machine. With a little drafting knowledge, you can solve many, many problems.

One of the keys is to have a good drafting scale. Since my shop equipment is graduated in inches, I use engineering scales graduated in inches for design work. These things can help you quickly make layouts to scale; such layouts are good checks against calculations. I've attached a picture of my beloved 6 inch drafting scale. That thing has so much use on it that the maker's name has worn off the scale. But I remember that it was made by Post (I got it in the late 60's).

If you buy a drafting scale, make sure it's accurate. I've got many of them and some of them are out a bit when I check them against my good Starrett machinist rules. Some of the best scales are the clear plastic ones (by e.g. Vemco, Mutoh, etc.) that are made for drafting machines. These are wonderful to use and just plain dead accurate. They're still being made.