Rivets should not be placed so close that the material between them is unduly injured by pushing or that the driving tool or "dolly" will interfere with one rivet when driving the other; likewise they should not be placed so far apart that the material between them will separate or open up. Unless specified otherwise in the specifica tions Table VI may be taken as good practice; for 1-inch, and 1-inch rivets, the minimum spacing is seen to be three diameters of the rivet.
The maximum spacing allowable is usually sixteen times the thickness of the thinnest plate they go through. The minimum and maximum limits placed above are not to be used wherever possible. Few engineers consider it advisable or permit spacings less than 2-1 inches and 3 inches, or more than 4 inches and 5 inches for 1-inch and finch rivets, respectively.
The minimum limits above refer to the center to center of rivets, while the maximum values refer to the distance center to center measured along the gauge line or line along which the rivets are placed.
Gauge lines may be single, Fig. 40a, or double as in Fig. 40b. The gauge of a shape is the distance of the gauge line from a certain base. In the angle it is the back, in the channel it is the back, while in the I-beam it is the bisecting line of the web.
The gauges for standard channels and 1-beams are given in the handbooks of manufacturers, such as Cambria, Carnegie, etc., which books also give the size of rivet or bolt which can be used in the flange of any certain I-beam or channel. This does not mean that the size of bolt or rivet there given must be used in the web also, in fact, ;-inch and Finch should be used in the web, no matter what size is specified for the flange.
The standard gauges for angles are given in Table VII.
While a double gauge is shown for a 5-inch leg, it is very undesirable to use it. Do not use 5-inch legs with double gauge lines. Likewise, do not use a single-gauge line on an angle with a 6-inch leg or more, unless specially told to do so by those higher in authority.
In the spacing of rivets in crimped angles, the distance "b", Fig. 41, should be 11 inches plus twice the thickness of the chord angles, but never less than 2 inches.
The grip of a rivet is the length under heads after the rivet has been driven. The length of a rivet is the length of the shank before
the rivet is driven, Fig. 42, these lengths for various grips being easily found in any manufacturer's handbook.
Care should be taken in case of castings to add -1. inch more to those values given.
Rivets may have two full heads or may have one or both beads countersunk or flattened or any combination. Such conditions are signified by certain signs, all of those in common use being listed in the handbooks already referred to, and also shown in Table V.
A rivet can be driven as close to a projection as one-half the diameter of the head plus I inch. This requires a special "dolly".
1 i The dolly generally used requires This is about 11 inches for a i-inch rivet and about 18 inches for a 1-inch; see Fig. 43 and Table V. In some instances a special gauge, that is, one other than given in Table VII, is used. In such cases care should be taken to see that the distance A, to the fillet, or curve of the angle, is sufficient, otherwise the dolly could not come down evenly and an imperfect head is the result. When rivets are staggered, it is necessary to know how close they may be spaced in order that they may not be less than the minimum allowed distance center to center. Table VIII gives the distances center to center of rivets for given values of the spacing and gauge line. The tances below and to the right of the upper zigzag line are large enough for 1-inch rivets while those below and to the right of the lower zigzag line are large enough for i—inch rivets. For example, if the gauge "g" was 11 inches, the spacing must be at least 2 inches in order that the distance center to center would not be less than 21 inches, the rivets beings inch. If the rivets were 1 inch, the spacing must be 1 inches or more in order to have the distance center to center not less than 24 inches. These values are found by going down from the value 11 inches in the top row until a value equal to or just greater than the 21 or 21 inches is found, and then following across to the first column where required spacing is found.
Care should also be taken that the rivets arc not so close that there will not be at least 1" between the holes in the direction of the line of stress, see Fig. 43d.