Page 243 - My FlipBook

USE OF RUBBER DAM. 241

Fio. 207. Fig. 209.

perspective by Fig. 208, a, h, c,
(L The holes in the rubber may

Fig. 208.

a bed 1
"1 - 'r
r--"
Diagrammatic drawing : form of valve.

be formed with a punch of suit-
able size, which should be forced
upon the end of a close-grained
piece of hard wood. They may
be made with a little practice
by drawing the rubber over a
round-ended instrument w'ith
some force and pricking the
rubber at a suitable point with
a sharp knife, when a round
section escapes. The difference
in size of the holes is deter-
mined by the distance from the
end of the instrument at which
the puncture is made. The deter-
mination, however, of size and The Ainsworth punch.
distance is not easily made in
this manner. The best appliance for the purpose is the Ainsworth
punch (see Fig. 209), with which complete control of size and distance
may be easily effected.
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