10), so that the sides shall
take the weight directly, and the nails only have to keep the rungs firmly
in position. The objection to notching-in is that it reduces the strength
of the ladder, which is of course only that of the wood between the bottom
of the notches and the plain side. Therefore it is necessary to have sides
somewhat deeper than would be required for a centrally-runged ladder;
which is pierced where the wood is subjected to little tension or
compression.
[Illustration: Fig. 10--House ladder and details of letting in a rung]
Materials.--The length of the ladder will decide what the stoutness of
the sides should be. For a ladder about 12 feet long, such as we propose to
describe, larch battens 3 by 1-1/8 inches (actual) in section and free from
knots, especially at the edges, will be sufficiently strong to carry all
reasonable weights without danger of collapse. But be sure to get the best
wood obtainable. The rungs may be of 2 by 1 inch stuff, though 2 by 3/4
inch will suffice for the upper half-dozen, which have less wear, and are
shorter than those below.
Pages:
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35