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The Mounting 3
Another design is shown in Fig. 71, where a minimum of machining is called for. For this design, not less than 1 1/2" pipe and fittings should be used, and preferably a size larger. The lengths of pipe which make up the polar and declination axes are turned perfectly round in the lathe, taking a minimum cut
for the purpose. The internal threads of the tees are bored out only enough for the
trued-up pipe to be fitted snugly into them. The faces of the tees ought also to be
faced off, square to the boring.
A third and perhaps the most satisfactory way of employing pipe fittings is shown in Fig. 72. In this design, 1" pipe is used for the axes, with l½" fittings, and the intervening space is filled with babbitt metal. This gives a very smooth, rigid bearing, and it is possible in the construction to align the axes perpendicular
to each other with good precision.
For the permanent mount, where weight is not a factor, 1 3/8" solid bar stock is preferred to pipe, which must be machined perfectly round in the lathe. Bar stock is ground truly round, and it is only necessary to have the local plumber cut the pipe thread on it. Be sure in so doing that the vise jaws do not grip that part of the shafting that is to be encased in babbitt, as the resultant dents will cause trouble. Machined collars to fit the 13/8" shafting can be purchased at the hardware store.
It ought not to be difficult to interest a local plumber sufficiently for you to borrow the paraphernalia requisite for the babbitting job — a fire pot on which to melt the babbitt, a solder pot, ladle, and torch. Or it is quite feasible to bring the assemblage to his shop and do the job there under his guidance. The entire operation of melting the babbitt and pouring a bearing may not take more than 15 minutes. About three to four pounds of babbitt will be needed for the bearings, but a surplus is needed for the pot, and may be used later in casting a counterweight. Use a good grade of babbitt; the difference in the cost of a few pounds is top small
to risk deformation of a bearing that is almost pure lead. The babbitt must be heated to a point where a piece of cardboard will char if thrust into it.
The babbitted bearings
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