August 7th, 2004


No, that's wrong...

Last night, I built a foam-core model of the storage shed that I'm planning on building. It doesn't provide a lot of construction details, but it does at least provide a sense of the look of the building. And I made a little version of myself at the same scale to see how big it actually is compared to me.

My design uses a 6/12 pitch roof, meaning for every 12 inches of lateral distance, the roof rises 6 inches. It is a little shallower than the roof of the actual house, but my semi-devious plan is to make it look like a mausoleum so that I can dress it up for Halloween, and it actually comes out really close. I even designed double swing-out doors for the front, and a matching removable panel for the back so that I can route people through it if I want to.

I like the way the mock-up looks, so I'm using that as my base for the CAD drawings. I've spent most of today doing detailed CAD drawings of the framing. I got the foundation and floor joists and decking in perfectly, and I was doing fine until I came to the roof trusses.
The first round, I ended up screwing up the dimensions of the wood so I had to start over. Finally I finished the drawings, and was starting to add the dimensions, when I noticed that the angular dimension that I was looking at seemed... wrong. It was telling me that my acute angle was 26.57°, when it should have been 30°.

Clue to me that I got something wrong. So I checked. And rechecked. I found nothing.

So I drew a simple right triangle, 12" high and 24" wide. As in 12.0000 inches by 24.0000 inches. And sure enough, the acute angle is 26.57°. And it shows up as 0.46 radians.

Am I insane? Have I forgotten a basic principle of math, or is my CAD program wrong?

Edit: Nope, it was me. The computer is right.

Now I can either redesign it with the correct angle, or trust that I can cut a 26.57° angle (or a 63.43° angle) with my trusty power miter saw.