The plain mangle racks are shown in Figs. 103 and 104, the former of which has teeth on the inside of the opposite parallel limbs, and the latter, [Fig. 104], having teeth not only on the parallel sides, but also around the circular parts at the ends.
This form of rack may be modified so that an alternate circular motion will be produced during the movement of the rack in either direction. [Fig. 105] is such an instance. A pinion within such a rack will turn first in one direction, and then in the next in the other direction, and so on.
If the rack is drawn back and forth the motion imparted to the pinion will be such as to give a continuous rocking motion to the pinion.
Controlling the Pinion.—Many devices have been resorted to for the purpose of keeping the pinion in engagement with the teeth of the mangle rack. One such method is shown in [Fig. 106].
The rack A has at one side a plate B, within which is a groove C, to receive the end of the shaft D, which carries the pinion E. As the mangle rack moves to such a position that it reaches the end of the teeth F on one limb, the groove C diverts the pinion over to the other set of teeth G.
All these mangle forms are substitutes for cranks, with the advantage that the mangle gives a uniform motion to a bar, whereas the to and fro motion of the crank is not the same at all points of its travel.