Fig. 2509.
To put on the second crank, we first place the shaft so that the crank already on stands exactly horizontal, setting it by placing a spirit-level, as shown in [Fig. 2508], in which a represents either the crank-pin journal or the crank-pin hole in the crank, and b a circle struck on the end face of the shaft and from its centre, the diameter of the circle b being exactly the same as that of a. If then we so adjust the position of the crank that a spirit-level applied to the exact circumferences of the circles a and b stands level, the crank will stand level, and we have only to put the second crank on with its centre-line standing perpendicular, and the two cranks will be at a right angle one to the other. We now proceed to put on the second crank, pursuing the same method employed in putting on the first one, save that the temporary key need not be inserted so far into the keyway, because, if the keyways have been cut the least out of true, it will make a great difference at the crank-pin, because of the increased distance of the latter from the centre of the crank-shaft. As soon as the second crank is placed to its position on the shaft we must ascertain if it stands vertical, which we may do by applying the spirit-level as shown in [Fig. 2509], bringing its edges exactly fair with the edges of the circles a and b, and moving the crank until the bubble of the level stands true, and taking out the temporary key if it is necessary to adjust the crank at all.
If, however, the crank is to be forced on by hydraulic pressure, this latter adjustment should be made when the crank is just sufficiently far on the crank shaft to enable it to bind enough to well support its own weight, to facilitate which the end of the shaft is sometimes slightly tapered for a very short distance—a practice which is sometimes rendered unnecessary by reason of there being attachments fitted to the hydraulic presses which of themselves adjust the position of the cranks, and insure their being at a right angle one to the other.
After the cranks are on their places the keys may be fitted, care being taken that, if the crank last put on had to be moved to adjust it, the sides of the keyways be filed even, otherwise driving the key will tend to move the crank.
Fitting Engine Cylinders.[35]—When engine cylinders are made in quantities, as in locomotive building shops, a great deal of the fitting work is saved by the machine work; but when a single cylinder or a pair of cylinders only are to be fitted up it will not pay to make jigs and appliances; hence, they are usually fitted up entirely by hand. The first thing to do is to mark off all the holes requiring to be drilled, and have the drilling done.
[35] From the “Complete Practical Machinist.”
In marking the holes in the cylinder covers it is to be noted whether that part of the cylinder cover which fits into the cylinder has a portion cut away to give room for the steam to enter (as is usually the case), and if so, first mark a line across the inside flange of the cover, parallel to the part cut away, and then scribe each end of the line across the edge of the flange. Then mark a similar line across the cylinder end, parallel to the steam port where it enters the cylinder, and scribe each end of this line across the cylinder flange, so that, when the cylinder cover is placed into the cylinder and the lines on the flanges of the cylinder and the cover are placed parallel to each other, the piece cut away on the cover will stand exactly opposite to the steam port, as it is intended to do. The cover may then be clamped to the cylinder, and holes of the requisite size for the tap (the tapping holes, as they are commonly called) may be drilled through the cover and the requisite depth into the cylinder at the same time.