Having completed the revolving member, we now turn our attention to the magnet frame, fields, etc.
The details of the magnet frame are covered by Plate H. Certain dimensions here are fixed by the electrical design in order to give the proper amount of iron in the frame, the proper size field cores, and proper spacing of fields. The frame is made split horizontally at the center line, and the two parts are symmetrical, except that the lower half must have proper feet at the points where it rests on the base. Only one of the lower quarters, Figs. 1 and 2, is shown in the drawing, since this will give all necessary dimensions and instructions for the entire frame and the lower half is symmetrical about a vertical center line.
The work on this drawing consists mostly of locating and dimensioning the parts already fixed by the designer and completing the mechanical details. There are some very interesting things to be seen in connection with some, of these mechanical details. There is a pole on each side of the machine which must come exactly at the split, Fig. 2. The holes for the bolts which hold these pole pieces must come at a point which will clear the studs holding the two halves of the frame together. Also two of the poles come where the feet are located. It will be seen that the casting is made hollow at this point (see sketch marked Section "DD") and the bolts for these poles are put through from this space. The studs for holding the two halves of the frame together also come down into this space. A steel cover plate is provided so that the rough casting and bolt heads are covered and present a neat appearance. It will be noted that wherever a bolt head comes against the outside of the magnet frame, that place is spot faced, that is, faced off so as to give a flat bearing surface.
Details of Feet Several sections are shown through the feet so that their form is determined definitely all over. An enlarged view of the bead at the point where the two halves are joined is also shown. These sections and enlarged views help the pattern maker in laying out his pattern drawings, and are an essential part of the drawing.
The base, Fig. 11, is a single iron casting. While this is but a single piece, a great deal of detail is shown in order that the pattern maker and foundryman will have sufficient information. It will be noted that the casting is hollow, with supporting ribs at intervals to add strength and stiffness, and with bosses on the surface where the magnet frame and pedestals are supported. These latter must, of course, be carefully machined to give the frame and bearing pedestals the proper relative location. This plate also shows the shims, Fig. 12, used for adjusting the height of the magnet frame in order that the armature may be properly centered in the field. These shims are similar in every way to those used for the pole pieces, and serve a similar purpose.
Note in this drawing again, we have an example of the partial picture, the base being symmetrical about the center line of the machine.