Building the Traditional Hewn-Log Home

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In the formula, we'll let H represent height, C represent the width of the chinking gap, and R represent rise; we'll be solving for the common notch depth, which we'll call D.

With all that in mind, here's the formula:

D = 1/4 (H + C - R).

In English, that means that the common notch depth for a round of logs is equal to one quarter of the sum of average log height plus chinking height minus the rise of the upper notch. Again, H derives from a straightforward measuring and averaging of log heights, and C is an arbitrary figure that depends primarily on how wide you want the chinking gaps to be. (Peter uses 1 " for straight, smooth logs, and 11/2" to 2" for crooked, knotty logs.) But how the heck do we find R?

To determine R (rise), we need to know two things: the hewn thickness of the logs, and the pitch of the slanting top notch. Notch pitch is arbitrary (within limits), so long as it remains constant for all the corner notches in a structure. For half-dovetail notches, Peter prefers a pitch of 1:3-that is, a rise of one inch for every three lateral inches. (You can cut a 1:3 template from Masonite or other thin stock; a vertical leg of 6" and a base leg of 18" will give the hypotenuse—the side opposite the right angle—the desired pitch of 1:3.)

Since 6" is a common wall thickness, we'll use that figure in our example. To find R (rise), we simply divide wall thickness by notch pitch-which, in our example, would be 6 divided by 3 equals 2. (Remember the rule of one inch of rise for every three inches of wall thickness and you're in business.)

So, with R (rise) = 2, C (chinking gap height) = 1, and H (average log height) = (let's say we came up with) 11, we can work through the formula as follows:

D = 1/4 (11 + 1 - 2) = 2-1/2.

Let's do that again, this time in English: 11 plus 1 is 12, minus 2 is 10, and 1/4 of 10 is 2-1/2.

That's all there is to figuring the common notch depth for all the bottom notches in a round: The deepest part of every bottom notch in our hypothetical round will rise to 2-1/2" below the centerline.

But how do you apply that to the upper notches, which are higher on their inside faces than on their outside faces? On which face do you mark the 2-1/2"? The answer is . . . neither; the notch depth for the upper notch, since it slants down toward the outside, must be measured at the log's horizontal center point. And how do we get a ruler and pencil into the center of a log to put a mark at the 2" point?

We don't. Instead, we employ another simple algebraic formula. Since both upper and lower notches are laid out from the inside face of the log, we must mathematically extend that 2" R (rise) height from the horizontal center of the log to where it would intersect the inner face. The formula we'll use is this:

U = D + 1/2 (R).

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