Now mark out accurately the centres of the discs on both sides, and make
marks to show which face of each disc is to be outside.
On the outside of both scribe circles of the size of the bearing tubes, and
other circles at the proper radius for the bolt hole centres.
On the outside of D scribe two circles of 2-inch and 1-11/16-inch radius,
between which the steam pipe will lie.
On the inside of D scribe a circle of 1-27/32-inch radius for the steam
ports.
On the outside of E mark a 7/8-inch circle for the exhaust pipe.
On the inside of both mark the circles between which the ring must lie.
Bolt Holes.--The marks for these, six or twelve in number, are equally
spaced on the outside of one plate, and the two plates are clamped or
soldered together before the boring is done, to ensure the holes being in
line. If the bolts are to screw into one plate, be careful to make the
holes of the tapping size in the first instance, and to enlarge those in D
afterwards. Make guide marks in the plates before separating, between what
will be the uppermost holes and the circumference.
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