The Shutter.--The woodwork is so simple that nothing further need be said
about it. The more difficult part of the business is the making of the
shutter, which must be so constructed that it can be opened and closed
rapidly by motions similar to those used in working the telegraph key
described in a preceding chapter. Speed of working is obtained by dividing
the shutter into two or three parts, each revolving on its own spindle, but
all connected so as to act in perfect unison. The thinnest sheet brass or
iron obtainable should be used, so that the tension of the spring used to
close the shutter need not be great. Our illustration shows a two-part
shutter, each half an inch wider than the hole in the front, and jointly a
similar amount deeper. The upper half overlaps the lower, outside, by a
quarter of an inch.
The spindles are two straight pieces of brass wire, revolving in sockets
which are most easily made of notched pieces of wood (as shown in Fig.
189), with removable caps of strip tin. The lower spindle should be an inch
longer than the width of the front, to allow for a cranked end, to which
the closing spring will be attached.
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