which let A A represent the axis of one shaft, and B that of the other
of the pair of bevil wheels that are to work together, their axes
meeting at W; draw the line E at a right angle to A A, and representing
the pitch circle diameter of one wheel, and draw F at a right angle to
B, and representing the pitch circle of the other wheel; draw the line G
G, passing through the point W and the point T, where the pitch circles
or lines E F meet, and G G will be the line of contact of the tooth of
one wheel upon the tooth of the other wheel; or in other words, the
pitch line of the tooth.

[Illustration: Fig. 241.]

[Illustration: Fig. 242.]

Draw lines, as H and I, representing the tooth breadth. From W, as a
centre, draw on each side of G G dotted lines, as P, representing the
height of the tooth above and below the pitch line G G. At a right angle
to G G draw the line J K; and from where this line meets B, as at Q,
mark the arc _a_, which will represent the pitch circle for the large
diameter of the pinion D. [The smallest wheel of a pair of gears is
termed the pinion.] Draw the arc _b_ for the height, and circle _c_ for
the depth of the teeth, thus defining the height of the tooth at that
end. Similarly from P, as a centre mark (for the large diameter of wheel
C,) arcs _g_, _h_, and _i_, arc _g_ representing the pitch circle, _i_
the height, and _h_ the depth of the tooth. On these arcs draw the
proper tooth curves in the same manner as for spur wheels; that is,
obtain the curves by the construction shown in Figures 237, or by those
in Figures 238 and 239.

To obtain the arcs for the other end of the tooth, draw line M M
parallel to line J K; set the compasses to the radius R L, and from P,
as a centre, draw the pitch circle _k_. For the depth of the tooth draw
the dotted line _p_, meeting the circle _h_ and the point W. A similar
line, from _i_ to W, will give the height of the tooth at its inner end.
Then the tooth curves may be drawn on these three arcs, _k_, _l_, _m_,
in the same as if they were for a spur wheel.

Similarly for the pitch circle of the inner and small end of the pinion
teeth, set the compasses to radius S L, and from Q as a centre mark the
pitch circle _d_. Outside of _d_ mark _e_ for the height above pitch
lines of the tooth, and inside of _d_ mark the arc _f_ for the depth
below pitch line of the tooth at that end. The distance between the
dotted lines as _p_, represents the full height of the