ON THE CONSTRUCTION OF JOINTS
In uniting two or more elements, some particular type of joint is
necessary. In framing timbers, in making braces, in roof construction
and supports, in floor beams, and in numerous other places, where
strength is required, the workman should have at his command a knowledge
of the most serviceable methods.
Illustrations can most forcibly convey the different types; but the
sizes must be determined by the character of the material you are
working with. Our aim is to give the idea involved, and the name by
which each is known.
[Illustration: _Fig. 292. Bridle Joints._]
Reference has been made in Chapter X, to certain forms of scarfing and
lapping pieces. This chapter has to do with a variety of other
structural forms, but principally with such as are used in heavy
building work, and in cases where neither fish plates nor scarfing will
answer the purpose.
[Illustration: _Fig. 293. Spur Tenon._]
[Illustration: _Fig. 294. Saddle Joints._]
BRIDLE JOINTS.--This is a form of joint where permanency is not desired,
and where it is necessary to readily seat or unseat the vertical timber.
It is also obvious that the socket for the upright is of such a
character that it will not weaken it to any great extent.
SPUR TENON.--This tenon can be used in many places where the regular one
is not available. This, like the preceding, is used where the parts are
desired to be detachable, and the second form is one which is used in
many structures.
SADDLE JOINT.--This is still another manner in which a quickly
detachable joint can be constructed. The saddle may be mounted on the
main base, or cut into the base piece. An infinite variety of forms of
saddles are made, most of them being used in dock work, and for framing
of that character where large timbers are used, as in the building of
coal chutes, and the like.
[Illustration: _Fig. 295. Joggle Joints._]
[Illustration: _Fig. 296. Framing Joints._]
JOGGLE JOINT.--This joint is used almost exclusively for brace work
where great weight must be supported. The brace has a tenon, and the
end must also be so arranged that it will have a direct bearing against
the upright, which it braces and supports, or it may have two faces, as
in the second figure, which is an exceedingly strong construction.
[Illustration: _Fig. 297. Heel Joints._]
[Illustration: _Fig. 298. Stub Tenon._]
FRAMING JOINTS.--These are the simplest form in which two members are
secured together. They are used almost wholly in rafter work, and have
very few modifications. The depth of the cut, for the toe of the rafter,
depends on the load to be carried, and also on the distance the end of
the rafter is from the end of the horizontal member on which the rafter
rests.
HEEL JOINTS.--This is by far the most secure of the framing type of
joints. This, if properly made, is much better than the construction
shown in the previous illustration, but the difficulty is to make the
rafter fit into the recesses properly. This is no excuse for failure to
use, but it is on account of inability to make close fits that is
accountable for lack of use. It will be seen that in case one of the
heels rests against the recess, and the others do not, and the pressure
is great, there is a liability to tear out the entire joint.
[Illustration: _Fig. 299. Tusk Tenon._]
STUB TENON.--This is another form of tenon which is made and designed to
be used where it is in close proximity to another tenon, or where the
mortises, if made full size, will weaken the member. The long tusk can
be shortened, to suit the place where it projects, and the stub tenon on
each side of the tusk may be made very short, and one side longer than
the other if necessary.
TUSK TENON.--Two forms of tusk construction are given. Any number of
forms have been devised, all for special purposes, and designed for
different kinds of woods. These shown are particularly adapted for soft
woods, and the principal feature that is valuable lies in the fact that
they have a number of shoulders within the mortise, each of which,
necessarily adds to the strength. It should be observed that in the
construction of the tusk tenon, the greatest care must be taken to have
it fit the mortise tightly, and this has reference to the bottom and
shoulder ends as well.
[Illustration: _Fig. 300. Double Tusk Tenon._]
DOUBLE TUSK TENONS.--The distinguishing difference between this and the
preceding is in the tusk, which in this form of construction goes
through the upright member, and is held by a cross key. The double tusk
is intended for hard woods, and it is regarded as the finest, as well
as the strongest, joint known.
COGGED JOINTS.--This differs from the regular tenoning and mortising
methods, principally because the groove or recess is in the form of an
open gain. It is used where the member is to be inserted after the main
structure is put together.
[Illustration: _Fig. 301. Cogged Joints._]
[Illustration: _Fig. 302. Anchor Joint._]
ANCHOR JOINT.--This form of connection is designed for very large
timbers, and where great care must be taken in making the parts fit
together nicely, as everything depends on this. This style is never
used where the angles are less than 45 degrees, and the depth of the
gain in the timber receiving the brace is dependent on the thrust of the
brace.
[Illustration: _Fig. 303. Deep Anchor Joint._]
The Deep Anchor Joint is an extension of the tongue of the Anchor tenon,
so that it affords a greater support for the end thrust. To clearly
distinguish between this and the preceding form, it might be said that
the Anchor Joint is one designed to protect the member containing the
gains, while the Deep Anchor Joint favors the brace, by giving it a
greater power.