This section is from the book "Safe Building", by Louis De Coppet Berg. Also available from Amazon: Code Check: An Illustrated Guide to Building a Safe House.
WHEN it is necessary to secure two or more pieces of iron or steel together in such a manner that they can be readily separated, bolts are used. These are iron or steel pins with solid heads at one end and threads cut on the other end, onto which the nut is screwed, thus holding the two pieces together. How closely the two pieces may be held together depends, of course, entirely upon the man who handles the wrench. Then too, bolts or pins do not completely fill the holes through which they pass, which frequently is a cause of great weakness, besides the danger of water getting into the spaces and rusting them. Where, therefore, it is not necessary to ever separate the pieces - and the latter are of either wrought-iron or steel - rivets should be used, which, for all practical purposes, might be considered as permanent bolts or pins. Cast-iron, of course, always has to be bolted, as it would break if riveting were attempted on it. A rivet is a piece of metal (wrought-iron or steel) with a solid head at one end and a long circular shank. In its shortest description the process of riveting consists in heating the rivet, passing its shank through the two (or more) holes, while hot, and then forging another solid head out of the projecting end of the shank. The hammering forces the heated shank to fill all parts of the holes, and the shank contracting in its length, as it cools, draws the heads nearer together, thus firmly forcing and holding the pieces together. Rivets are made of mild steel or the very best wrought-iron, the latter being the most reliable. According to some writers, the shank is made, tapering in length and circular in shape, being larger at the head and smaller at the end. In this country, however, the shank is always of uniform diameter. The length of shank from head to end varies with the thickness of pieces to be riveted together, but is long enough not only to allow for passing through the pieces, but has also enough additional length to provide for filling of holes and forming head, the additional length being about 2 1/2 times the diameter of hole. The rivets are manufactured by heating rods of the diameter of rivets, which arc pushed while hot into a machine, which at one operation forms the head and cuts off the shank to the desired length.
Description of Rivet.
Length of Tail.
The shank before heating is about one-sixteenth smaller in diameter than the hole, to allow for its expansion when healed, i'. e., for
3" rivets, 13/16" hole, are punched and for 7/8", 15/16" holes. There are four kinds of rivets, all answering the same uses, and only distinguishable by the shapes of their heads. These are the button or round headed rivet: the conical h e a d e d rivet : the pan or fiat headed rivet; and the countersunk rivet. The latter is only used when a smooth surface is desirable. The first is the most used shape. Figure 103 shows the different shapes, the dotted lines indicating how the second head is finally shaped. Sometimes a rivet is countersunk on one end only.
The exact sizes of heads, shapes, etc., vary in different mills. The diameter of head should he from 1 1/2 to 2 times the diameter of shank,1 according to shape adopted and the height of head should be about 2/3 the diameter of hole. In countersunk work, the head may extend entirely through the plate or not, its diameter being accordingly smaller or larger. Where it extends through the sharp edges will shear the rivet, countersinking therefore, should be avoided in the plates. In showing riveted work the diameter of the shank is always drawn and Figured where the hole is to he left open and the size of rivets is spoken of accordingly, the hole is always made 1/16"larger. Where the riveting is to he done at the shop or mills, the size of head is shown. The spacing of rivets will be considered later, the direct distance from centre of holt to centre of hole is known a. the
Size of Head.
Pitch of Rivets.
1 The Franklin Institute standard for button beads (which are usually used in the United States) is to make the head 1/2" larger than 11 /2 times the diameter of shank.
"pitch." The pitch should never be less than 2 1/2 diameters; nor should the centre of any hole (if possible) be nearer to any edge than 1 1/2 diameters. By diameters is understood the diameter of shank. In riveted angle work the distance is frequently necessarily less. In thick plates it should be more. In drilled work the pitch might be reduced to 2 diameters. If rivet-heads are countersunk the pitch should be increased, according to the amount of metal cut away to make room for the rivet-head.
In punching rivet-holes the position of holes are usually marked off on a wooden template and then through this marked or indented by a hand-punch on the iron plate; the plate is then passed under a punch which is usually worked by steam-power, the die and the punch being adjusted to the size of the rivet-hole wanted, the punch is usually 1/16" larger than the rivet, and the die about 1/8" larger. The thickness of plates to be punched should not, as a rule, be greater than 3/4 of an inch; nor in any case should the thickness of plate be as large as, nor larger than, the rivet-hole, as, unless the diameter of the hole is larger than the thickness of the plate the punch is apt to break. Where holes are punched at the building, small screw or hydraulic (alcohol) punches are used, which can be readily carried around by one or two men, the power being obtained by screwing or pumping; or sometimes, where mechanics are not quite up to the times, a rather more clumsy lever-punch is used, the power being obtained by increasing the direct pressure by leverage. Punching makes a ragged and irregular hole, and as it gives the plate a sudden blow or shock it injures the metal considerably, unless the rivet-holes are so close, that the entire plate is practically cold-hammered. The loss in strength to the remaining fibres in a punched wrought-iron plate is about 15 per cent, this loss being, of course, in addition to the loss of area, and it is a loss that cannot be restored. In steel plates the remaining fibres are damaged about 33 per cent, but in them the loss can be restored by annealing the plate which, however, adds considerably to the expense.