The dovetail, or box, corner (figs. 6 and 7) is a strong corner, and
considerable experience is required in order to make a neat-looking
job. This type has several undesirable features: (1) The logs are apt
to develop a wide crack because the corner is framed from the part of
the log in which the least shrinkage occurs, and (2) since the logs are
hewed down to form the corner, the wood has a tendency to collect and
retain moisture which soon results in decay. Also, this corner detracts
noticeably from the "loggy" appearance so characteristic and desirable in
log structures. The drawings in figure 6 show the most practical methods
of marking and framing the dovetail, or box, corner.
The flat, or plain, tenon corner (fig. 8), is also common. It may be
made in two ways. In one, only the bearing surfaces are framed, while in
the other, all four sides of the tenon are framed flat. The plain tenon
corner does not have the highly desirable feature of being self-locking.
However, it is simple to make and economical, and therefore especially
suitable for temporary structures. The logs must be pinned together, as
shown in figure 11. All the framing can be done on the ground, before the
logs are put in place. Carefully fitted, this makes a neat-looking job.
_Directions for constructing the flat, or plain, tenon corner._--Square
one end of log, as in figure 8, at point _A_, then measure required
length and saw the opposite end square, at _B_. If the log has any
curvature, turn it on the skids until its back is up. Determine the
thickness of the tenons, based upon the average top and butt diameters
of the log. Then take an 18-inch length of board the same width as the
thickness of the tenons, driving a nail through its center and into the
center of the log. Place the spirit level on top of the board and mark
lines on the log at the top and bottom edges. The width of a tenon
varies with the diameter of the logs; 8- to 10-inch diameters will
produce 6- to 7-inch wide tenons.
[Illustration: Figure 6.--Marking and framing the dovetail, or box,
corner.]
[Illustration: Figure 7.--Ranger Station, Lolo National Forest, Mont.
Note the meticulous construction of box corners.]
[Illustration: Figure 8.--Framing the flat, or plain, tenon corner.]
Nail a 1 inch by 1 inch cleat on the pattern board to points _C_ and _D_
and then make saw cuts on each end, cut chip off and smooth the surface.
Turn log over and repeat on the other side. After framing out the sides
of the tenon, the log is ready to be placed on the wall. Some fitting
between corners is usually necessary but, if the logs are fairly straight
and smooth, the work will be minimized.
The upright, or groove-and-tenon, corner (fig. 9) is used to a
considerable extent in the West. It has desirable features from a
mechanical standpoint: (1) The weight of the building is carried on
the full length of the logs and does not rest solely on the corners,
as in other types, and (2) it makes a tight wall because no openings
will develop between the logs. Although not difficult to construct, the
upright corner requires considerable mechanical skill and accuracy.
A good carpenter can frame the entire building on the ground before
any logs are placed on the foundation, after which it can be erected
in a very short time. Next to the round-notch corner the upright, or
groove-and-tenon corner, probably has the best appearance.
[Illustration: Figure 9.--Framing the upright, or groove-and-tenon,
corner.]