embodiment for cutting a hemispherical surface on a hob in this embodiment the cutting tool moves along a curved path represented by the arrows 37 thus during the period which the drill bit 30 engages the surface 26 of the hob 24 the bit enters the hob with a lateral downward movement and exits the hob with a lateral upward movement as shown in fig1 the resulting elongated dimple 38 is shown in fig1 and 17 it is elongated but blunted at the ends thereof in comparison with the dimple 34 of fig1 and 15 this is because of the angle at which the drill bit enters and leaves the hob thus as shown in fig1 the deepest portion of the dimple defines a line l 2 which is curved at its opposite ends the dimple 38 also has equal major axes a u2032 u2033 fig1 shows an alternate embodiment for producing a dimple 38 configured as in fig1 and 17 the cutting tool 28 is stationary and the hob 24 is pivotable through an arc with respect to the drill bit the description of fig1 13 above is for a cutting tool or hob being displaced within a plane in a first direction to produce the dimples 34 or 38 of fig1 and 16 it is also possible to displace the cutting tool or hob in a second plane during drilling to produce a dimple whose major axes are not co linear such a dimple 40 is shown in fig1 and 19 and has a kidney shaped configuration by way of example only the dimple 40 has first and second semi elliptical portions 40 a and 40 b the.