Fig. 1551.
The Whitworth quick-return motion is represented in [Fig. 1551]. At p is the pinion receiving motion from the cone pulley or driving pulley of the machine and imparting motion to the gear-wheel g, whose bearing is denoted by the dotted circle b. Through b passes a shaft c, which is eccentric to b and carries at its end a piece a in which is a slot to receive the pin x, which drives rod r whose end z is attached to the ram of the machine. At d is a pin fast in gear-wheel g and passing into a slot in a.
Taking the position the parts occupy in the figures, and it is seen that the axis of b is the centre of motion of g and is the fulcrum from which the pin d is driven, the power being delivered at x. The path of motion of the driving pin d is denoted by the dotted circle h′, and it is apparent that as it moves from the position shown in the figure it recedes from the axis of c, and as the motion of g is uniform in velocity therefore d will move a faster while moving below the line m than it will while moving above it, thus giving a quick return, because the cutting stroke of the ram occurs while d is above the line m and the return stroke occurs while d is below m.
Fig. 1552.
In some constructions the pin x and pin d work in opposite ends of the piece a, as shown in [Fig. 1552]. This, however, is an undesirable construction because the shaft c becomes the fulcrum, and as the power and resistance are on opposite ends of the lever a, the wheel g is therefore forced against its bearing, and this induces unnecessary friction and wear.
We may now consider the tool motion given by other kinds of slide operating mechanism.
