Wednesday, April 24, 2013

Doin' Sum Math - A Good Sine

I'm working on making a little covered rack for the firewood to put behind the barn. Pretty simple construction - 4x4 corner posts and some 2x4's to hold the logs and fasten the roof sheets to. The roof is going to have a 3/12 pitch but in order to set the proper angle on the miter saw the 3/12 has to be converted to a degree measurement or you can solve it several other ways. Lay out the boards with the framing square or easier still with a Speed Square and cut to the line. Since the ends of the rack are only 3' wide by 6' high just lay it out on the floor and transfer the angle with a sliding bevel gauge. Easy to keep things square when putting it together that way as well.

However, when I was at the high school I did a little unit on layout every year so the boys would be exposed to at least a little higher level math. I had a handout that had some of the most common conversions as well as the common trig functions. We'd run through some sample problems using both the trig tables in the back of a couple of my old books and solving it with a scientific calculator. The main point was that if you want to solve for any angle or side of a right triangle, you could do it in a matter of seconds with the proper tools. Really easy, so no reason not to be able to do it.

Until you retire and can't find a math book or a scientific calculator. Took me about ten minutes the other day going through some of my junk to find the book. I used to keep it in the bottom left drawer of my desk when I was at the high school - two high schools in fact. Don't know how long I've owned the book but I bought it for a buck. It was originally published in 1917. Even though it's close to 100 years old, the answers are still right. Unlike the calculator I came up with. I found it right away but couldn't figure out why the answer kept coming up wrong. Side opposite divided by the side adjacent, hit the second function button, TAN and Viola! Except it was wrong. Been so long since I had used that calculator for anything other than balancing the checkbook, I had neglected to set it to degrees before I started.  Now both the book and the calculator are going to take up residence in the wood shop. "You'll use 'em if you can find 'em."

If you asked the average guy the tools he'd want to set up a new shop you would expect things like a table saw, miter saw, etc. I'd definitely add a cheap scientific calculator to the tool box. I know they make some spiffy construction calculators but they don't normally sell for under ten bucks like the cheapy one I've got. Plus I've had it for damn near twenty years. Fifty cents per year? Definitely a good investment there. As far as I'm concerned the cheap calculator ranks up there with movable type and the cordless drill. Throw in a good engineering manual and you're all set.

On a tangentially related note, sticking with the math theme, Dorkpunch posted up a little ditty on the 14th about what constitutes a good teacher. For a young guy, he's got it pegged pretty well. Nothing earth shattering there but it's good to reflect on why you're doing what you do. I had a chance encounter with a retired history teacher yesterday morning while getting a tire repaired on the old Dodge. I'm guessing he was 75 +/-. Interesting to get the take on the job from a guy roughly 15 years my senior after reading what Dorkpunch had to say. The job has changed a lot over the years but the qualities that make up a good teacher? Probably the same since Socrates.


Rich said...

Scientific calculators are a weakness of mine. I must have 25-30 of them all over the place. Never could leave one on a garage sale table or at a flea market. Seems like a senseless act, selling a calculator for a quarter, or even a buck. But I guess you have to remember what it was like before they existed, which I do (barely). Nice post... Rich

Shop Teacher Bob said...

I was an engineering student for a while in the late 60's. Texas Instrument had just come out with a scientific calculator for something like $125.00 - big money then. Everyone could see they were the future but I still had to buy a fancy slide rule that I used for only one semester. I used to drag it out and use it once in a while just to remember how. In fact I used to keep a little 6" one in my tool box with my machinist tools. Now? Pick up a cheap calculator at the Dollar Store or, like you, at the garage sale and there you go. Eight decimal place accuracy for less than a dollar. Hard to beat that.

Traveling Pirate said...

As I was reading this, I thought, "You're not set to degrees, STB." But, you figured it all out. You're no trig newbie. I spent many a day teaching Physics saying, "Are you in degrees?"

Shop Teacher Bob said...

Like they say - "If you don't use it, you lose it". I actually had a layout on the floor when I decided to do the math just for shits and giggles. I did have a cheapie calculator out there but no math book with trig tables. Figured it was a good time to get set up. I'm golden now.