It is best quality wood free from imperfections in
straight strips one yard long and of a uniform width of about 5/8
in. As to thickness, any multiple of 12-point (about 1/8 in.) may
be obtained, thus saving much work in fitting up joints. Fifty
cents will buy enough wood for an entire instrument. All corners
are carefully mortised and braced with small brass angle-pieces.
The frame is held together by small brass machine screws. After
much experimentation with bearings, it was found best to make them
in halves as metal bearings are usually made. The loose half is
held in place by guides on all four sides and is tightened by two
screws with milled nuts. A great deal of trouble was experienced
in boring out the bearings until the following method was devised.
One hole was bored as well as possible. The bearing was then
loosened and a bit run through it to bore the other. Finally, a
piece of shafting was roughened by rolling it on a file placed in
both bearings and turned with a brace. The bearings were gradually
tightened until perfectly ground.
The declination axis must be perpendicular to both the hour axis
and the line of sight over the pointer.
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