Make a pattern out of cardboard by cutting a 6-inch by 12-inch rectangle, then cutting the top at an angle so one side is only 10 inches long.
Prop the log so it's lying the way you want it to be in the finished house. If it has a hump or slight twist or is just unevenly hewed, lay it how it looks best and you can cut the dovetails to compensate. Snap a horizontal chalk line along the side of the log in the approximate center, using a carpenter's level to make sure the line is level.
Lay the pattern against the butt end of the log with the slanted side of the pattern up and angled down toward what will be the outside of the house. Use a level to make sure the sides of the pattern are vertical. Trace the slanted line on the log.
Using a level, draw a horizontal line along the inside and outside of the log, starting where the slanted line ends. Make the lines as long as the width of the other log which will cross this log.
Using a level, draw vertical lines up from the horizontal lines. Draw a line across the top of the log to connect them. These lines outline the area you need to cut out to make the top of the dovetail.
Repeat the same steps on the other end of the log, placing the cardboard pattern the same height above the chalk line that you snapped.
Cut out the top of the dovetail by sawing down the vertical line, then sawing or chiseling from the butt of the log to cut out a roughly wedge-shaped piece. Repeat on the other end of the log.
Roll the log over and prop it so the sides of the cardboard pattern are vertical when the slanted part of the pattern is placed against the cut on the butt end of the log. Using a level, draw a horizontal line across the butt end of the log, near the top. If the log is perfectly rectangular you can simply use the top edge of the log, but if it's hand-hewn or out-of-square, this horizontal line will make the dovetail fit properly.
Place the cardboard pattern on the side of the log, with the slanted side oriented so the higher part of the slant is aligned with the end of the line you just drew. Trace along the pattern. Repeat on the other side of the log.
Using a level, draw a vertical line up from the end of the lines you just drew and draw a line to connect them across the top of the log. You've now marked the area you need to cut out to create the bottom of the dovetail. Repeat the same steps on the other end of the log.
Cut out the marked area by sawing down the vertical line and sawing or chiseling along the other. If you're using a chisel, this will be a little harder than before, since you'll be chiseling at an angle across the grain. Repeat on the other end of the log.
Repeat the same steps on other logs and they'll fit together when placed on top of each other.
Things You Will Need
- Chalk line
- Carpenter's level
- Chalk or pencil
- Crosscut saw or chainsaw
- 2-inch chisel and mallet
- You can use a hewing hatchet to rough out the chiseled areas, then finish with a chisel. The spacing of the logs can be adjusted by changing the distance between the top and bottom of the dovetail cuts. If they're closer together, the logs will sit closer to each other. There's no need to cut the underside of the dovetail on the first two sill logs, since they'll rest on the foundation without a log beneath them.