|
Machining the Parts 3
6. Screw the spare coupling on the free end of the polar-axis nipple, and hold it in the independent chuck, running true, with the tailstock center supporting the tee end (Fig. 78). Machine the surfaces indicated by the heavy lines. For further machining, it is necessary to remove the nipple from the tee, but first, to insure later return of the parts to the same exact positions, a small hole into which a pin or screw can later be inserted should be drilled through the two parts, as is indicated in the diagram. (A No. 44 drill, tap size for a 4-36 screw, will do.) After removing the
coupling and unscrewing the nipple, reverse the assembly in the chuck and turn off the tops of the threads at the other end.
7. The faces of the reducing tee must now be machined, parallel to each other, and at right angles to the branch face. The small center hole in the back of the tee is enlarged to allow entry of a long screw which threads into a 3" length of flat bar stock, which is then drawn firmly against the machined branch opening of the tee. Hold the tee in the chuck (Fig. 79) and adjust until a tool point just contacts the surface of the flat bar evenly, along its length, as the lathe carriage is moved along the ways. Thus insuring that the face of the flange will now be made quite square
with the branch opening, remove the bar. The face and outer shoulder of the tee can now be machined, and the internal threads at that end bored out. Reverse the tee in the chuck and repeat the operations at the other face, making both outside diameters equal. The faces should be parallel to each other within about 0.001".
8. Only one face of the second tee need be machined, but as it may be desired to put a collar on the lower end of the polar axis, it is best if both faces are machined
parallel to each other. The internal threads must, of course, be bored out. This
tee should first be experimentally made as tight as possible with close nipple
and elbow, and the face that will be uppermost marked for identification, for example, by spot drill- Fig. 79. Operation 7-Facing off into the shoulder with the tee, declination axis. a small drill, or by filing a notch in the edge.
9. The backs of both tees are now drilled and tapped for the clamping screws L, Fig. 72. Tinning the inside of the tees to provide more secure anchorage for the babbitt is optional.
10. Four collars, preferably of aluminum because of its light weight, must be turned up either from solid stock or from castings, and bored out to suitable diameters to provide a neat fit on the shafting. Make the faces of these collars parallel and square with the boring. The outside diameters should be concentric with the borings, and of the same diameter as the shoulders of the tees.
This will facilitate easy centering of the shafting when you are getting ready to babbitt. The width of the collar at the upper end of the polar axis should be such as to bring the intersection of the axes vertically over the center of the tripod (see Fig. 73). The collar at the upper end of the declination axis ought to be at least 1" wide. The width of the other collars is optional, and they should be provided with two set screws each, spaced 120° apart.
machining the parts part4
|
|
