The Library of Work and Play: Mechanics, Indoors and Out

by Fred. T. Hodgson

Figs. 148, 149. Dynamometer—Pantagraph

[Fig. 149] represents a pantagraph for copying, enlarging and reducing plans. One arm is attached to and turns on the fixed point C. B is an ivory tracing point, and A the pencil. Arranged as shown, if we trace the lines of a plan with the point B, the pencil will produce it double the size. By shifting the slide attached to the fixed point C and the slide carrying the pencil along their respective arms, the proportions to which the plan is traced will be varied.

[Fig. 150]. Anti-friction bearing. Instead of a shaft revolving in an ordinary bearing, it is sometimes supported on the circumference of wheels. The friction is thus reduced to the least amount.

[Fig. 151]. Releasing hook used in pile-driving machines. When the weight W is sufficiently raised, the upper ends of the hooks A, by which it is suspended, are pressed inward by the side of the slot B, in the top of the frame; the weight is thus suddenly released, and falls with accumulating force on to the pile-head.

[Fig. 152]. A and B are two rollers which require to be equally moved to and fro in the slot C. This is accomplished by moving the piece D, with oblique slotted arms, up and down.

Figs. 150, 151, 152. Anti-friction—Drop hook—Regular motion

[Fig. 153]. Centrifugal check-hooks, for preventing accidents in case of the breakage of machinery which raises and lowers workmen, or ores, in mines. A is a framework fixed to the side of the shaft of the mine, and having fixed studs D, attached. The drum on which the rope is wound is provided with a flange B, to which the check-hooks are attached. If the drum acquires a dangerously rapid motion, the hooks fly out by centrifugal force, and one or other, or all of them, catch hold of the studs D, arrest the drum, and stop the descent of whatever is attached to the rope. The drum ought besides this, to have a spring applied to it, otherwise the jerk arising from the sudden stoppage of the rope might produce a worse effect than its rapid motion.

[Fig. 154]. A sprocket-wheel to drive or to be driven by a chain.