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Machining the Parts 2
When turning the nipples in the lathe, remove only a minimum amount of metal in order not to thin the walls any more than is absolutely necessary. Removal from the newly poured bearings will be made easy if, at the same time, the nipples are given a taper of about 0.001" for each inch of their length. Therefore, for those two
operations, the tailstock center should be offset about 0.008".
1. Make up the declination axis nipple in the heavy flange. Hold it in the chuck, running true, and cut off any excess length that protrudes beyond the back face, recessing it to about 1/32" below the face of the flange. At the same time bore out the inside of the nipple to a depth of about 1/4", removing a minimum of metal.
2. Turn up from scrap stock a metal plug to fit into the above bored-out end. Return the first assembly to the chuck and center-drill into the plug for the tailstock center.
3. Make up the polar-axis nipple in the reducing tee. The end will be seen to project inside where it will be in the way of the babbitt, so after noting the length of the excess projection, remove the nipple and cut this excess off, after which the nipple is returned to the tee. Hold the nipple in the chuck, running true, and center-drill into the back of the tee for the tailstock center.
4. The tailstock center is now offset about 0.008" away from the worker; the diameter of the work will thus be tapered in the direction of the chuck end, where it should be least.
5. A spare coupling is screwed firmly onto the end of the declination assembly, and held in the independent chuck with the tailstock center supporting it at the other end (Fig. 77). Adjust the chuck to run true. Machine all parts indicated by the heavy
lines in the diagram except the back face of the flange, which would be made conical instead of flat if done while the tailstock center is offset.
To face this surface, remove the coupling and hold the machined nipple in the chuck, running true. This will bring it reasonably square with the axis of the shaft. Reverse the assembly, holding the flange in the chuck, and turn off the tops of those
threads on the other end of the nipple that had been covered by the coupling.
machining the parts part3
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