It will be observed that one revolution of the crank bears the same relation to the number of teeth in the large wheel, as one tooth in the wheel to be cut bears to the whole number it is to contain. The number of teeth and the pitch of the wheel is consequently derived from the change gears.
When level gears are cut, the head is then set at the proper inclination, and secured by the screw which projects at the rear of the head.
The cheapness of this machine more particularly recommends it, the price being but $250, while its efficiency and regular operation are so well established as to require no further comment.
NO. 4.—THE UPRIGHT DRILL.
This is another admirable engine for diminishing and simplifying human labor. It is applied to the boring of all kinds of iron-work for machinery.
The perpendicular drill, as will be readily observed, is worked with a swift, rotatory movement, by means of the bevil gears at its upper extremity. By a wheel—the circumference of which only is displayed in the cut—acting upon the thread of a screw midway its length, it is pressed down upon the piece of work to be drilled.
This piece is secured upon a horizontal table placed under the point of the rotary drill, which table may be elevated or depressed at pleasure, by aid of the small lever projecting backward, which acts on a geared wheel playing on the thread of the great perpendicular screw of the main shaft.
NO. 5.—ENGINE LATHE.