e work supported by the
spindle during the rotary and longitudinal movement thereof, ...

Even before this patent was applied for, another patent was pending for
the purpose of modifying the pitch of the lead screw without the use of
change gears in spite of the wide acceptance of such gear mechanisms for
over a hundred years.

[Illustration: Figure 21.--A HOB-GRINDING MACHINE OF 1933, showing use
of the master screw with a modifier but without change gears. Carl G.
Olson's U.S. patent 1901926.]

[Illustration: Figure 22.--A SINE-BAR DEVICE to modify the effective
lead of a master lead screw without introducing a complex mechanism
which would be both difficult to make and to operate within the required
close limits. Carl G. Olson's (1933) U.S. patent 1901926.]

Figure 21 shows a plan view[7] of the machine, and figure 22 a detailed
view of the sine-bar mechanism actuated by the master screw, 6, to
modify the effective pitch of the lead screw in accordance with the
realities of practice as stated in the preamble of the patent:

This invention relates to material working machines, and
particularly to machines such as hob grinders and the like, wherein
the work is reciprocated through the agency of a lead screw.

In the manufacture of hobs it is common practice to employ the same
machine for grinding hobs of varied diameters, and in order to
employ such a machine in this manner the pitch of the lead screw,
thereof, which actuates the work carrier, must conform to the axial
pitch of the hob to be ground. This will be readily apparent when
it is understood that the helix angles of hobs vary in accordance
with their diameters and, consequently, the difference between the
normal pitch and the axial pitch correspondingly varies. While the
requirement for the normal pitch may be the same for hobs of
different diameters, it is necessary to change the axial pitch in
accordance with a change in the hob diameter, and this axial pitch
of the hob is equal to the pitch of the lead screw which actuates
the work carrier in grinding machines heretofore used. Hence, in
order to adapt such machines to cover a wide range of leads, it is
necessary to provide a large number of interchangeable lead screws
and obviously this represents a large investment, and the
interchanging of these screws requires the expenditure of
considerabl