Carpenter's Math for Dummies - The Freelance Files MMCXXIV

Marking rafters with a framing square

In the real world, where most of us – although fewer than a couple of years ago – live, we expect people who answer a question to know, or at least think they know, the answer. That's what "good faith" means, after all. That's not, unfortunately, true of internet content farms like eHow.com; where people who'd never taken on a task routinely told us how to do it based on a few minutes' research. Why anyone would believe them is, sadly, beyond us. It's why we're here, after all: to attempt to correct some of the bullshit these people sprayed around cyberspace. We found today's nominee, Donald Miller, trying to explain "Carpentry Math Problems" for HomeSteady.com.

Don't get us wrong; Miller didn't completely botch the assignment like so many other eHowians. No, he just lacked... vision. According to Don, most carpentry problems involve using a tape measure and then converting your measurements to square measurements and cubic measurements; even estimating materials (more on that later). Where Don's vision failed him is in failing to understand that there is more to carpentry than straight lines. 

One example is the roof: Miller fails to even mention pitch of a roof and how it's stated. The standard is rise in inches per run in inches: a 6/12 roof is steeper than a 4/12 roof, and a 1/12 roof (if there is such a thing) is darned near flat. A similar topic is the pitch of stairs, which even a DIYer might need to consider when building a deck. Luckily, there are people out there who know more than Don.

Miller also seems ignorant of one of the most basic rules of carpentry, the use of the 3-4-5 triangle to lay out right angles. That's such a neat trick you'd think he'd mention it, but no-o-o-o-o! There are lots and lots of math tricks for carpenters, many of them built into the carpentry tools. Oh, sure, most people know about the 16-inch (and 24-inch) marks on carpentry tape measure for standard stud spacing, but Did Miller even mention how a framing square is used for cutting rafters and stair stringers? The tricks of using a speed square? Nope, not a word.

Instead, Don concentrated on what appears to be the few things he's done in his limited DIY career, such as using 176 words to explain how to find half of a linear measurement (although he failed to explain why you might need to do so). Well, actually, Don talked about how one might cut a "10 1/2-inch board exactly in half.," 100 words or so later coming up with "5 1/4 inches." Unfortunately, he forgot the width of the saw kerf, so either one both is 5¼ inches wide and the other is 51⁄8 wide, or both are 53⁄16 inches wide. Let's just hope Don (and his readers) can accept the gap.  When it comes to area, Don only thought in terms of sheets of plywood... He covered the topic fairly well, but what about linear goods: how many running feet of 2¾-inch flooring planks will you need for a room fourteen feet by 21 feet? Now that involves math, Don! And you don't even have to get into "more rigorous geometric solutions"!   For the record, Don, ten feet of 2¾-inch flooring covers about 2.3 ft² of space, so you'll need about 1280 running feet of flooring to cover a 294-ft² room. Add the customary 10% or so overage for screwups, etc., and make it an even 1400.

Do that, and you won't be a Dumbass of the Day next time. Interestingly enough, Don claims a background in forestry. Too bad he wasn't around in time to answer the question addressed by our last DotD!

MM - CARPENTRY