In [Fig. 2005], for example, let a a represent the line of centres of the cutter and the wheel, and line b the plane of the front face of the tooth being ground; and in [Fig. 2006] let line a represent a vertical line from the axis of the wheel, and b a vertical line passing through the axis of the cutter, the tooth edge c occupying the same position in both figures. Now suppose we employ cutting edge c as a centre and swing the cutter until its axis or centre moves along the arc d to the dot e, and it is evident that during this motion the heel of the tooth will have approached the axis of the emery wheel and that more clearance will therefore have been given to the cutting edge c.
Fig. 2007.
The actual curve of the top face, as c, [Fig. 2007], of the tooth t will remain the same in either case, but its position with relation to the front face will be altered. As this curve is greater in proportion as the diameter of the emery wheel is diminished, and as the curvature weakens the cutting edge of the tooth, it is obviously desirable to employ a wheel of as large a diameter as possible.
Fig. 2008.
