Figs. 113, 114, 115. Blocks and rocker
[Fig. 117]. In this, rotary motion is imparted to the wheel by the rotation of the screw, or rectilinear motion of the slide by the rotation of the wheel. Used in screw cutting and slide lathes.
Figs. 116, 117. Crank and rotary motion
[Fig. 118]. Uniform circular into uniform rectilinear motion; used in spooling frames for leading or guiding the thread on to the spools. The roller is divided into two parts, each having a fine screw-thread cut upon it, one a right and the other a left-handed screw. The spindle, parallel with the roller, has arms which carry two half nuts, fitting to the screw, one over the other under the roller. When one half nut is in, the other is out of gear. By pressing the lever to the right or left the rod is made to traverse in either direction.
[Fig. 119]. A system of crossed levers, termed "lazy tongs." A short, alternating rectilinear motion of rod at the right will give a similar, but much greater motion to the rod at the left. It is frequently used in children's toys. It has been applied to machines for raising sunken vessels; also applied to ship pumps three quarters of a century ago.
