Columnar jointing

“ Narrow surfaces make better and safer joints than wide ones; they are more quickly repaired with file or scraper, and they are less liable to catch dirt at the moment of making a joint. The limit of narrowness is that required to resist strains that might crush the metal and spoil the face of the joint.
Unless the joint is made metal to metal, fitting without any orifice, the jointing material is always softer than the pipes or other things to be joined. In this way the jointing need not have dead-true surfaces, but, yielding under pressure, it adapts itself to the space it has to fill. ”

“ Fig. 102.—Joint with Single Dovetail Tongue and Groove.
Cabinet-work Joints.—With regard to tongued and grooved joints which apply more particularly to the jointing of cabinet work, Fig. 93 is produced by planes which are specially made for the purpose. One plane makes the tongue and another the groove. The handiest sizes to buy are those which joint 3⁄8 in., 5⁄8 in., and 3⁄4 in. timber, it being usual to dowel or loose-tongue thicker boards. ”

“ Joints and Joint-structure.—This is the most universal of all rock-structures, since all hard rocks and many imperfectly consolidated kinds, like clay, are jointed. Joints are cracks or planes of division which are usually approximately vertical and traverse the same mass of rock in several different directions. They are distinguished from stratification planes by being rarely horizontal, and from both stratification and cleavage planes by being actual cracks or fractures, and by dividing the rock into blocks instead of sheets or layers. ”

“ An Open Slot Mortise at the end of a right-angled frame is seen in Fig. 169. Fig. 170 shows an open slot mortise and tenon joint at the end of a frame of 60°. Both these joints are occasionally called end bridle joints.
Hammer Head Tenons.—At Fig. 171 is shown the method of jointing framing having semicircular or segmental heads. The left-hand diagram indicates the method of wedging the joint so as to draw up the shoulders; the right-hand view shows the tongueing of the shoulders, which is necessary if thick timber has to be wrought. ”

“ In the erection of a high trestlework viaduct for the Havana Railroad, Bollman apparently became concerned with the tensile weakness of cast iron when applied in long, unsupported columns. Although a column is normally subjected to compressive stresses, when the slenderness ratio—that is, the length divided by the radius of gyration of the cross section—becomes great, a secondary bending stress may be produced. If this stress becomes great enough, the value of the tensile stress in one side of the column may actually exceed the principal compressive stress, and a net effect of tension result. ”

“ They must be limited to the zone of fracture, and most of them are probably much more narrowly limited. Joints frequently end at the plane of contact of two sorts of rock. Thus a joint extending down through limestone may end where shale is reached.511 Joints are frequently offset at the contact of layers or formations, and a single joint sometimes gives place to many smaller ones. All these phenomena are to be explained on the basis of the different constitution and elasticity of various sorts of rock. Generally speaking, rigid rock is more readily jointed than that which is more yielding. ”

“ Joints cut right across the bedding, and are often variously combined, one set of joint planes traversing the rock in one direction, and another set or sets intersecting these at various angles. Thus, in many cases the rocks are so divided as easily to separate into more or less irregular fragments of various sizes. Besides these confused joints there are usually other more regular division planes, which intersect the strata in some definite directions, and run parallel to each other, often over a wide area: these are called master-joints. ”

“ Fig. 62.—The Two Pieces of a Halved Joint.
The tools used for making joints of the above class are: planes, the gauge, tenon or other saw, chisels, try square, and in some cases a joiner's bevel to obtain and mark the necessary angles, pencil and marking knife.
Plane up the face side and face edge of the timber, gauge and plane to both thickness and width; mark shoulders with pencil or marking knife; gauge to the thickness of the required halving; saw waste portions away; pare up with chisel to a good fit ”

“ The lateral bending of a column produces a combination of bending with compressive stress over the section, the compressive stress being maximum at the section of greatest deflection on the concave side. The convex surface is under tension, as in an ordinary beam test. (See Fig. 6.) If the same stick is braced in such a way that flexure is prevented, its supporting strength is increased enormously, since the compressive stress acts uniformly over the section, and failure is by crushing or splitting, as in small blocks. ”

“ Finite Bending of Thin Rod.—The equation
curvature = bending moment ÷ flexural rigidity may also be applied to the problem of the flexure in a principal plane of a very thin rod or wire, for which the curvature need not be small. When the forces that produce the flexure are applied at the ends only, the curve into which the central-line is bent is one of a definite family of curves, to which the name elastica has been given, and there is a division of the family into two species according as the external forces are applied directly to the ends or are applied to rigid arms attached to the ends ”

“ In all the structures raised by the engineer, in beams, pillars and girders of every kind, provision has to be made, somehow or other, for strength of two kinds, strength to resist compression or crushing, and strength to resist tension or pulling asunder. The evenly loaded column is designed with a view to supporting a downward pressure, the wire-rope, like the tendon of a muscle, is adapted only to resist a tensile stress ”

“ These causes, however, are not believed to affect rock structures to any considerable depth. Torsional joints and joints due to earthquake vibrations appear to be special phases of tension-joints.
Two or more sets of joints may also be produced by compression, the number being dependent on the complexity of the folding. Many compression-joints correspond in direction with planes of shearing. They are often associated with minor faulting and with slaty cleavage.
Tension-joints appear to be much more widely distributed than compression-joints. ”

“ It is very rarely the case that fixed joints have their pins subject to simple compression in the direction of their length, though they are frequently subject to simple tension in that direction. A good example is the joint between a steam cylinder and its cover, where the bolts have to resist the whole thrust of the steam, and at the same time to keep the joint steam-tight. ”

“ From a constructional point of view Fig. 101 is far and away the best joint that has yet been produced. Unfortunately, however, there is not at the present time any hand tool that will economically produce it, owing probably to the fact that the joint is the subject of a patent. The dovetail tongue tapers slightly throughout its entire length, gripping the joint on the principle of the wedge and squeezing the glue into the pores of the wood. ”

“ C.J.H. Woodbury who replies that the method followed by the best mill-builders is to bore a hole along the axis one and three-fourth to two inches in diameter. The method formerly used was to bore the hole in half-way from each end after the column was finished, but as the auger would follow the grain of the wood, the holes would not always meet, and running out nearer the side of the column would produce structural weakness which has been revealed in tests of columns whenever destructive tests of such columns have been made. ”

“ A correct method to adopt is seen at Fig. 6. Here we have supported the joint by rearing up against the wall [Pg 4] a couple of pieces of batten, one at each end of the board, thus supporting it throughout its entire width until the glue is thoroughly set. The two or more pieces of timber in a butt joint adhere by crystallisation of the glue and atmospheric pressure. A well-fitted joint made with good quality glue is so strong that, when boards of 3 feet and upwards are jointed together by this method, the timber in most cases will break with the grain sooner than part at the joint. ”

“ A second mode of generation is no less admirable: If we make the spiral of Archimedes the base of a right cylinder, and imagine a cone of revolution having for its axis the side of the cylinder passing through the initial point of the spiral, then this cone cuts the cylinder in a curve of double curvature. The perpendiculars to the axis drawn through every point in this curve form the surface of a screw which Pappus here calls the plectoidal surface. ”

“ This joint is seldom used in actual practice. The separate parts are given in Fig. 56.
At Fig. 57 are shown two cross rails and an upright halved together. This type of joint is used where three [Pg 24] pieces meet, as is the case in building the framing of a poultry house. The joint is nailed together.
Fig. 59.—Cellarette Partition Joints.
Fig. 58 is the end view of an ordinary workshop trestle, showing the application of dovetailed halving [Pg 25] where the legs have a tendency to strain outwards. The inset sketch of joint shows the housing of the top rail to receive the legs. ”

“ Joints in cisterns, etc., are generally made by scraping the edges clean with a steel scraper, and applying some lamp-black and size by means of a brush to the parts beyond, leaving a bright space of an inch or so on each side of the joint, a ladle of melted solder is then gradually poured on the joint and rubbed down with a piece of greased cloth, the lamp-black and size preventing the solder adhering to any part but that left bright, and in this way a straight neat joint is produced. ”

“ The link which connects two joints in the actual structure may be of any shape, but in the diagram of the frame it is represented by a straight line joining the points representing the two joints. If no force acts on the link except the two forces acting through the centres of the joints, these two forces must be equal and opposite, and their direction must coincide with the straight line joining the centres of the joints. If the force acting on either extremity of the link is directed towards the other extremity, the stress on the link is called pressure and the link is called a "strut." ”

“ The prime essential in a well working harmonograph is a properly constructed universal joint. Where such a joint is made with pivots for its bearings, one pair of pivots are very liable to have more friction than the other, which retards the movement and causes the harmonograph to undergo a continuous change of axis. ”

“ The column may therefore be considered as a hollow tube, of the section just described, and of the same form at each end, having at its extremities horizontally projecting rings called SNUGS, through which the bolts are passed, to fasten the columns to the connecting-pieces and base-pieces. That the hollow form adopted for the columns is that best suited to obtain the greatest strength with the least amount of material has been abundantly shown by experiments, as even two straws placed in an upright position will bear a very considerable weight ”

“ In the case of hollow columns, the exterior diameter must be cubed, and the cube of the interior diameter deducted from it when the relative values of different-sized columns can be compared. For transmitting motion, and here torsional stiffness is referred to, the resistance of shafts of equal stiffness is proportional to the fourth power of their diameters. ”

“ The shortest distance from the base to the apex is the line from point 1. Therefore, with point 1 as a center, arcs are drawn from points 2, 3, and 4 of the half-profile, cutting the base of the cone as shown in Fig. 200. With the apex as a center, arcs are drawn from each intersection of the base of the cone. Any point on the arc from point 1 is selected and is connected with the apex. This line will serve as the starting line of the pattern. The compass is set equal to the distance between any two divisions of the half-profile. ”

“ Interlocking Chair Joint.—A joint designed with a view to strengthening the construction of chairs at the point where they are weakest is shown in Fig. 189. The joint is an interlocking one so arranged that, once the chair is glued up, no motion of the side rail can be possible. The groove in the side rail tenon is cut in such a manner that, on the insertion of the back rail tenon, the joint actually draws up and, having done so, is locked in position. ”

“ This excess of diameter at the base being determined, the reader is to ask himself how 86 most easily and simply to smooth the column from one extremity to the other. To cut it into a true straight-sided cone would be a matter of much trouble and nicety, and would incur the continual risk of chipping into it too deep. Why not leave some room for a chance stroke, work it slightly, very slightly convex, and smooth the curve by the eye between the two extremities? you will save much trouble and time, and the shaft will be all the stronger. ”

“ The stresses in the web of a deep steel girder are not known, and the web is strengthened by a liberal number of stiffening angles, which no expert can figure out to a nicety. The ultimate strength of built-up steel columns is not known, frequently not even within 30% ”