Figure 3-59.-Hollow-chisel mortising machine.
Mortises are cut mechanically on a hollow-chisel
mortising machine like the one shown in figure 3-59.
The cutting mechanism on this machine consists of a
boring bit encased in a square, hollow, steel chisel. As
the mechanism is pressed into the wood, the bit takes
out most of the waste while the chisel pares the sides
of the mortise square. Chisels come in various sizes,
with corresponding sizes of bits to match. If a
mortising machine is not available, the same results
can be attained by using a simple drill press to take
out most of the waste and a hand chisel, for paring
the sides square.
In some mortise-and-tenon joints, such as those
between rails and legs in tables, the tenon member is
much thinner than the mortise member. Sometimes a
member of this kind is too thin to shape in the
customary reamer, with shoulder cuts on both faces.
When this is the case, a barefaced mortise-and-tenon
joint can be used. In a barefaced joint, the tenon
member is shoulder cut on one side only. The cheek
on the opposite side is simply a continuation of the
face of the member.
Mortise-and-tenon joints are fastened with glue
and with additional fasteners, as required.
Figure 3-60.-Dovetail half-lap Joint.
The dovetail joint (figure 3-49) is the strongest of
all the woodworking joints. It is used principally for
joining the sides and ends of drawers in fine grades of
furniture and cabinets. In the Seabee units, you will
seldom use dovetail joints since they are laborious
and time-consuming to make.
A through dovetail joint is a joint in which the
pins pass all the way through the tail member. Where
the pins pass only part way through, the member is
known as a blind dovetail joint.
The simplest of the dovetail joints is the dovetail
half-lap joint, shown in figure 3-60. Figure 3-61
shows how this type of joint is laid out, and figure 3-
62 shows the completed joint.
Figure 3-61.-Laying off 10° angle for dovetail