## Dovetail Notching

Half-dovetail notches are even simpler to cut than V-notches. The process is the same, except that you cut just one slope on the logs instead of two. The half-dovetail notches always slope down across the grain of the lower log to the outside. As before, scribe upward with parallel lines.

As with a cutting edge, you try to find a compromise angle for the slopes of the dovetails. The steeper the slope, the greater the interlock, but the more fragile the notches become. This is a good excuse to go study the log buildings in your part of the forest. Eventually, even the most deeply ingrained cultural patterns adapt to the strength of the local timbers.

V-notched and half-dovetail joints lock at the tops of the logs, but they can kick outward at the bottom. Full dovetail notches lock in the bottoms of the logs as well. To keep the notches strong as you chop them, V-notched and half-dovetailed logs can be left long and cut flush after the walls are laid up. Full-dovetailed corners are easier to lay out (and explain) if the logs are already cut to length.

I say easier—full dovetails can tax your powers of visualization, so we'll enlist some left brain arithmetic to help.

To completely close the gap between logs, the notching needs to remove half of each log's height. If the height of the log is divided into 16 parts, then half of that is 8 parts. If we made plain, flat, square notches, taking 4 parts from the top and 4 parts from the bottom of each log, that would add up to 8 parts—half the height of the log. Such square notching would close the gaps between the logs, but it would have no interlock at all.

Dovetail notching interlocks the logs, often using a 3-4-5 rule to still add up to 8 parts — closing the gap and creating the interlocking angles at the corners. Abstracted, the corners work like this:

345 parts up from the bottom of the upper log, over

543 parts down from the top of the lower log, makes

I have no evidence to prove a connection, but a framing square, with its standard 2-inch blade and 1 1/2-inch tongue is perfectly proportioned to lay out dovetail corners on 8-inch-high logs. Dividing an 8-inch-high log into 16 parts gives you 1/2 inch. The 1 1/2-inch tongue gives you three parts. The 2-inch blade gives you 4 parts (the width of the blade). The 5 parts is tricky. Starting at a point indicating 4 parts, drop back 3 parts (the width of the tongue). This gets you to 1 part. From there, go up 4 parts (the width of the blade again) and you've got 5.

Full dovetails securely interlock the logs at the top and bottom yet still shed the rain.

With other log heights, you can make a template. This is simply a board, twice as long as the logs are thick. Make it 3 parts of the log height wide at one end and 5 parts wide at the other end. This makes the midpoint 4 parts wide.

You need precisely hewn and regular timbers for full dovetails. The timbers have lost any resemblance to logs and the structure is anything but a cabin. Moravian settlers brought this disciplined manner of building into North Carolina, and it certainly must have impressed the English.