Sand Joint

Sand Joint is formed by turning down the edges of a lid or cover and making them dip into a continuous groove filled with sand. It is nearly air-tight, and is used with some kinds of stoves to render the lid of the outer casing smoke-tight.

Screw Joint

Screw Joint is made by means of a screw, which is a cylinder having its surface cut so as to leave a projecting spiral ridge, thread, or worm, whose inclination to the axis is constant. The screw is turned into a hole drilled and tapped to an exact counterpart and called a female screw, the tapping not being required, however, in the case of wood screws or screw nails, owing to the facility with which metal threads tap their own channels in most kinds of wood. Before the introduction of the socket joint the parts of iron mains used to be screwed together - a practice which is said to have led to some breakage through hindering expansion and contraction, which it must be observed cannot be much with properly interred pipes. Mains, indeed, are supposed to go with the ground, and are therefore kept low enough to avoid the chilly influences of frosty air, but in these instances, doubtless through imperfect threading and bedding, the screw ends were unequally strained, which sudden changes of temperature sufficiently augmented to produce fracture. Lengths of wrought iron barrel are united with screw sockets and red lead cement with or without a thread of yarn. In order that a screw may be as strong against the shearing off of its thread as against its rupture by direct tearing asunder, the depth of the overlap of the male and female threads should be theoretically about one-half the least effective diameter, and in practice this is doubled, as mentioned under Bolted Joint in Section VI., the depth of the overlap being made equal to the diameter.

Screw Shackle Joint

One form has been already described under the term adjustable, and its nature will be found immediately below under the head of Shackle Joint. The form of the shackle is of little consequence so long as it admits of regulating to a nicety the length of the tie whilst it holds the halves of the rod, which it tightens up, with sufficient rigidity. Fig. 92 represents one of many forms. Tension rods to principals and tie-bolts to strutting to floors are provided with screw shackles for adjustment; and screwed ends at all points of connection of sections of tension rods, when the latter are of considerable length, are advisable in lieu of welds.

Screw Shackle Joint 93

Fig. 92.

Shackle Joint

Shackle Joint is made with a shackle which, if not worked by a screw, consists of some such contrivance as a curved or stirrup-shaped bar, through whose extremities pass a single wedge, or a pair, in order to limit and control the tension of the tie-rod, etc, and consequently the free action of the piece it keeps in place. It is often omitted, however, and the consequence is that suspension rods, tension rods, and diagonal ties, etc, are either too slack or too much strained. The shackles used in building are composed as for other purposes, of a more or less simple arrangement of links, pins, and rods, but in order to admit of adjustment they must be provided with screws or cotters.