We come logically then to the armature flanges and the spider.
The two flanges are quite similar in everything except as regards their mounting on the spider. The one for the back end of the armature, Fig. 2, merely slips back over the arms of the spider against a shoulder. The laminations are placed on the spider, and then the front flange, Fig. 1, must be arranged to press the laminations against the back one, and must be held solidly in place. Note that the inside diameter of the back flange is given in decimals to a thousandth of an inch and marked spider fit. Now note the corresponding dimension on the front flange. While the dimension is an even eighteen and one-half inches it is given to three decimals, indicating that the machining must be done so that the given dimension is within one thousandth of an inch. This shows the workman at once where the fine work is to be done and, compared with other dimensions, shows the relative care which must be taken to make the size as shown.
This drawing also shows, very clearly, how a whole piece may be covered in the drawing by showing only a part. Nothing whatever could be added to the drawing by showing the whole of these two flanges, while more space would be required and more time would be needed to draw it.
It will be noted that the sections are identified on the plans by lines drawn across them at the points where the sections are taken, these lines being lettered, and a note added below the section giving the proper reference.
Another thing should be noted as showing how the draftsman must consider the pattern maker. The pattern maker must make proper allowance for shrinkage and for machining, and wherever a part is marked "finish" by means of the usual /, he will add to the dimensions shown in making his pattern. Now note the arms of these flanges, shown in section on Figs. 1 and 2. Instead of putting the / across the surface to be finished, a note is given which tells the pattern maker that, while it is to be rough finished, no extra allowance is necessary.
This simply illustrates the original point of the whole matter; the drawings are for the shopman, and every point, no matter how small, must be covered so that there can be no doubt in his mind as to how to proceed.
Now, taking up the spider, Fig. 3, it will be seen that the outside dimensions are determined by those of the flanges. The shaft diameter must now be calculated, if not given by the designer, and we can proceed to complete this drawing.
Note how the center of the spider is cored out to save metal, how fit dimensions are carefully marked in and given in decimals where close work is desired. Note the keyways for laminations, front flange, and shaft, and note how the keys are called for in the table in the corner.
Another point of interest is the way in which the draftsman has shown a section through one arm of the spider but has shown the other one full. By "bending" the section line A B C he has added clearness to the drawing and saved crosshatching considerable space. As to this crosshatching, many drawing rooms save time by the method shown here. Instead of making the usual parallel lines, the space is filled in with a pencil, giving a clouded appearance when blue-printed.
On the left end of the spider are shown the shoulder and tapped holes for the equalizer support. The equalizer support cannot be drawn until the equalizer rings have been laid out and the dimensions determined (See Plate E).