In the case of a channel it is the back of web rather than the center which is always located. For the holes for connections of a channel, therefore, the position of the back of channel is fixed, and then each hole in the group forming the connection must be located with respect to the back of channel as the group is not central with regard to the back. For an example of this see Fig. 196. It always adds to the clearness to put near each group of holes forming a con nection for other beams the size of beam or channel connecting to it. Holes at ends of beams for connecting to columns or for anchors are generally spaced by an independent set of measurements from the end of the beam.
The student should note that beams cut by the mill without special directions being given are subject to a variation in length of .?-; in. tinder or over the length specified. If the beam rests on walls such variation is unimportant. If, however, it frames between col umns and has 'soles connecting to the columns, such variation could not be allowed. For this reason measurements of such beams should always be marked "exact" or else at end of the sketch should be printed "column end in. clearance ". With such instructions, or similar directions in other cases to indicate how the beam rests with respect to other work, the mill will take the necessary precautions. In the case of framed beams, for instance, such notes are not sary, as it is self-evident that no variation at these ends can be allowed. Fig. 196 shows a beam framed into another beam, the relations of the top and bottom flanges being such as to avoid coping. Note here that it is necessary to give an end view to show the spacing of holes in the outstanding legs of connection angles. Note also the specification as regards these angles. If the connection is standard and is placed centrally with the beam, always say "standard connec tion". In such cases if the shop is familiar with the standards ferred to, an end view is not always necessary. If the connection is not placed centrally with the beam, or if the spacing of the holes in the legs varies any from the standard it is customary to write "stand ard connection, except as noted".
The first set of holes from the left-hand end in the web is for the connection of an 8-in. beam framed to this beam. Note that in., the spacing horizontally of these holes, and 21 in., the spacing verti tally, are the measurements in the outstanding legs of the standard connection for an S-in. I-beam.
The next set of holes in web are for the connection of a 4-in. beam which frames flush on top with the S-in. girder; this fixes the holes at 2 in. from the top as shown.
The single hole at the right-hand end is for a. standard anchor rod. This measurement of 2 in. from the end is a customary meas urement on such anchor holes, although some specification may call for something different.
In the flange near the left hand is shown a group of holes; these are for the connection of a channel which runs over the top of beam. As these holes are not symmetrical with regard to the axis used in locating the group, it is necessary to space each set with regard to their axis. These holes are spaced symmetrically with respect to the web of beam, and the distance between them is the standard gauge for punching the flange of an S-in. beam. Where holes come in a flange these standard gauges should always be followed unless there are special reasons for not doing so.
In the drawing, the plan of the bottom flange is given, although there are no holes in it. Where printed forms ready for filling in measurements and details are used, this would appear and it is added here for clearness. In actual details, however, it should not be drawn if it involves extra work and if there is no punching or cuts to be shown.
Fig. 197 shows a channel detail which is similar to Fig. 106 except that it is coped. In such cases, always specify the size and weight of beam to which it is coped and give the relation of the tops or bottoms, as for instance, "cope to a 12 in., 3q,-1b. I-beam flush on bottom", or "cope to a 12-in., 31k-lb. I-beam as shown". In case the beams do not cope flush on top or bottom, the outline of the beam to which it copes should be shown in red in the sketch, and the relations of flanges clearly indicated.
Below the sketch in beam details, is always given the specifica tion of size and weight of beam or channel and the overall length, the number of pieces wanted and the mark to be put on them. This specification is used by the mill in entering the order for its rolling list and it is important that it agrees with the detailed measurements in the sketch. Also if the beam is cut on a bevel the extreme length of beam required to give the specified bevel should he given. Fig. 19S shows a beam girder bearing a shelf angle for the support of wind joists, or a terra cotta arch of different depth from the beam. This requires an additional line of dimensions, giving the rivet spacing and the length and position of angles. The maximum rivet pitch of six inches is generally used. Where this angle interferes with connection holes or separator bolts, as in Fig. 198, it has to be cut, and in such cases the rivet pitch must be figured out to agree with the measurements fixing the connection holes or separators.