In writing dimensions the inches should be given as well as the feet, and in case the inches amount to nothing or to a fraction, a cipher should take the place of the inches.
It is not necessary when all rivets are shop rivets to draw in each in such cases to put in the end rivets and to inidicate the spacing and every rivet when the spacing is the same. It is only necessary of those which lie between but which are not shown. Fig. 3Sb illus trates this. in case of field rivets all rivets must be shown. No de parture from this rule should be allowed. Fig. 39 is an example of this. It is noted in this figure that although the spacing of many of the rivets is the same, yet all are shown in their proper place.
In placing dimensions where two or more members are detailed together, dimensions for the main member should run straight through from one end to the other. The dimensions of the larger member in so far as they are the same as the dimensions for the smaller may be used for the smaller member and additional or subdimensions be placed in con venient places in order to complete the detailing of the smaller mem ber. As an example of this see Fig. 3Sa where the edge distances and the method of detailing should be noted, and Fig. 39 also where the edge distances are the subdimensions. In Fig. 39 two dimen sions are given at one of the ends. This illustrates two methods of placing the same dimension. The dimension directly under the line of dimensions for the main member is placed in the preferable way. In the placing of subdimensions great care should be taken not to make them too small or to place them so that they interfere with the guide lines of the main dimension.
Notation. Used. As stated before, the feet and inches should always be given when a multiple space is given. For example they should be written thus: 5 © 6"=3'-0" 2 @ 3"=0'-6" © 4"=2'4" In single dimensions less than 1 foot it is not necessary to state the 0 for the foot, and, therefore, we have for example 4", 6", 11", etc., up to and including 12". A dash should always be placed between the feet and inches as shown above. Careful attention should be
paid to this detail since the omission of the dash may cause the dimensions to be considered as all feet or all inches and time and money will accordingly be lost.
In material notation the following are the rules: For angles the number should be placed first, the angle sign second, the dimension of the greatest leg next, then the small leg, then the thickness, and then the length in feet and inches.
For example, j 2-Ls 5"x 5 X For plates the number comes first, the abbreviation next, the width in inches next, then the thickness in inches, and finally the length in feet and inches.
For example, / -P/. /8 X 6 A- 2 -4 For beams and channels the number is stated first, next the depth in inches, then the weight in pounds per foot, then the sign, and finally the length in feet and inches.
For example, / # , 2 -I2' A' 5/2 Is x -2 5 -7 x 94 # Cs x /6r54 Zee bars are designated by their depth and thickness. The number is written first, the depth next, then the thickness, then the sign and finally the length in feet and inches.
Bars are designated by their number, then their size, or and finally their length in inches.
For example, Rivets and Rivet Spacing. Rivets are made in various sizes and are spoken of according to the diameter of their shank. Thus a i-inch rivet is one which has its shank inch in diameter. The heads of the rivets are not perfect hemispheres, being less in height than one half the diameter of the head. Table V gives the dimen sions of rivets of various diameters and their conventional represen tation in detail drawings. These dimensions are desirable on the drawings since they are often necessary in order to so figure the work that the material will not strike the heads. Rivets smaller than inch are seldom used except where the size of the material requires it. Rivets larger than inch in diameter are seldom used except in the heaviest work; and the beginner is advised not to use them until he has permission from those above him in charge.