In making wooden patterns wherefrom to cast the wheels, it is usual, therefore, to mark these lines on a drawing-board, so that they may be referred to by the workman in obtaining the degree of cone necessary for the body a b c d, to which the teeth are to be affixed. Suppose, then, that the diameter of the pinion is sufficiently small to permit the body a b c d to be formed of one piece instead of being put together in segments, the operation is as follows: The face d c is turned off on the lathe, and the piece is reversed on the lathe chuck, and the face a b is turned, leaving a slight recess at the centre to receive and hold the cone point true with the wheel. A bevel gauge is then set to the angle a b c, and the cone of the body is turned to coincide in angle with the gauge and to the required diameter, its surface being made true and straight so that the teeth may bed well. While turning the face d c in the lathe a fine line circle should be struck around the circumference of the cone and near d c, on which line the spacing for the teeth may be stepped off with the compasses. After this circle or line is divided off into as many equidistant points as there are to be teeth on the wheel, the points of division require to be drawn into lines, running across the cone surface of the wheel, and as the ordinary square is inapplicable for the purpose, a suitable square is improvised as follows: In [Fig. 161] let the outline in full lines denote the body of a pinion ready to receive the teeth, and a b the circle referred to as necessary for the spacing or dividing with the compasses. On a b take any point, as c, as a centre, and with a pair of compasses mark equidistant on each side of it two lines, as d, d. From d, d as respective centres mark two lines, crossing each other as at f, and draw a line, joining the intersection of the lines at f with c, and the last line, so produced, will be in the place in which the teeth are to lie; hence the wheel will require as many of these lines as it is to contain teeth, and the sides of the teeth, being set to these lines all around the pinion, will be in their proper positions, with the pitch lines pointing to x, in [Fig. 160].
Fig. 162.
Fig. 163.
Fig. 164.