The first method is the better, as cross boring of the sides greatly weakens them; but as the wedges may work out, an iron rod 5⁄16-inch in diameter should be placed below every eighth or ninth rung, and bolted on the outside for extra security.
The iron rods should not be used as treads instead of the wooden rungs as they offer an insecure foothold. The rungs are considered to be dangerous for use when they have been reduced by wear to one half of their original depth. The best rungs are made from old wheel-spokes, as they are well seasoned. The sides, which may be of sufficient length to receive 100 rungs, are 9 inches apart at the top and from 12 to 13 inches apart at the bottom, according to the length of the ladder.
Fig. 63
Fig. 64
Extension ladders are useful where, owing to the varying heights of the work, different lengths of ladders are required. The two halves of the ladder are connected in various ways, but if well made they are easily raised and lowered. They should be used only for the very lightest work, such as painting, cleaning down, &c.
Trestles.—Trestles are used chiefly by painters plasterers, and mechanics engaged on work that is not at a great height from the ground or floor level, and for which a platform is required. They stand from 6 to 12 feet in height, and the rungs should be sufficiently wide to carry three boards for the working platform. They are made of yellow deal, with mortised joints and wrought-iron hinges ([fig. 65]).
Fig. 65