As the
result of these considerations in the construction of the
machine, the surface of the glass 'comes up' regularly all over
the lens; and the polishing only takes a few minutes' work--thus
keeping the truth of surface gained by using a rigid tool."
The machine in question consists of a revolving sheave or ring,
with a sliding strip across its diameter; the said strip having a
slot and clamping screw at one end, and a hole towards the other,
through which passes the axis of the tool used in forming the
lens,--the slot in the strip allowing the tool to give any stroke
from 0 to 1.25 inch. The lens is carried on a revolving
turn-table, with an arrangement to allow the axis of the lens to
coincide with the axis of the table. The ratio of speed between
the sheave and turn-table is arranged by belt and properly sized
pulleys, and the whole can be driven either by hand or by power.
The sheave merely serves as a guide to the tool in its path, and
the lens may either be worked on the turn-table or upon a chuck
attached to the tool rod. The work upon the lens is thus to a
great extent independent of the error of the machine through
shaking, or bad fitting, or wear; and the only part of the
machine which requires really first-class work is the axis of the
turn-table, which (in this machine) is a conical bearing at top,
with steel centre below,--the bearing turned, hardened, and then
ground up true, and run in anti-friction metal.
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