27. A heart-cam, by whose rotation uniform traversing motion is imparted to the vertical bar. The dotted lines show the method of obtaining the curve of the cam. Eight concentric circles are drawn with radii in arithmetical progression as shown, and they are divided into twelve equal sectors. The points on the heart-curve are determined by the intersection of radii and circles.
28. A quick-return crank motion, applicable to shaping-machines. This arrangement needs no explanation.
29. A crank motion, with the crank wrist working in a slotted yoke, thereby dispensing with the oscillating connecting rod.
30. A screw stamping-press, showing how rectilinear motion may be obtained from circular motion by means of a screw.
31. A screw-cutting mechanism. The rotation of the left-hand screw produces a uniform rectilinear movement of a cutter which cuts another screw-thread (seen on the right). The pitch of the screw to be cut may be varied by changing the sizes of the engaged spur-wheels at the bottom of the frame.
32. The movable headstock of a turning lathe. By turning the wheel on the right hand motion is communicated to the screw, thus causing the spindle with the centre at its end to move in a straight line.
33. Swivelling-gear for car wheels. The essential part is the operation of the endless screw on the worm-wheel. The wheels are connected by a lever freely joined to the cranks.
34. Diagrammatic representation of screw-gear to operate three worm-wheels in the same direction, for chucks, etc. The method of working is obvious.
35. A mutilated screw for sliding into a nut having corresponding parts of the thread cut away, to be fixed by a partial turn. It is used for the breech-pieces of cannon.