uired radius (preparatory to gashing and bobbing the worm-wheel
teeth) by a formed tool _H_ held on the cross-slide.

[Illustration: Fig. 21. Second Operation on Bevel Gear Blanks]

=Turning Bevel Gear Blanks.=--Fig. 20 shows a plan view of the tools
used for the first turning operation on bevel gear blanks (these gears
are used for driving drill press spindles). The cored hole is beveled
true at the end by flat drill _A_ to form a true starting surface for
the three-fluted drill _B_ which follows. The hole is bored close to the
required size by a tool (not shown) held in the end of bar _C_, and it
is finished by reamer _D_. The cylindrical end of the gear blank or hub
is rough-and finish-turned by tools held in holders _E_ and _F_,
respectively. (These holders were made to set at an angle of 45 degrees,
instead of being directly over the work, as usual, so that the cutters
would be in view when setting up the machine.) It will be noted that the
chuck is equipped with special jaws which fit the beveled part of the
casting.

[Illustration: Fig. 22. Sectional View of Tapering Mold Shell which is
turned in Hartness Flat Turret Lathe, as illustrated in Figs. 23 to 27,
Inclusive]

The second and final operation on this blank is shown in Fig. 21. The
work _A_ is held by a special driver plate attached to the faceplate of
the machine. This driver plate has two pins which engage holes drilled
in the gear blank and prevent it from rotating. The blank is also held
by a bolt _B_ which forces a bushing against the cylindrical end. First,
the broad beveled side which is to be the toothed part of the gear, is
rough-turned by toothed cutters _C_, and a recess is formed in the end
of the blank, by a turning tool in this same tool-holder. A similar
tool-holder _E_, having finishing cutters, is then used to finish the
bevel face and recess. The other tools seen in the turret are not used
for this second operation. The rear bevel is roughed and finished by
tools and held on the cross-slide.

=Shell Turning Operation in Flat Turret Lathe.=--The "flat turret lathe"
is so named because the turret is a flat circular plate mounted on a low
carriage to secure direct and rigid support from the lathe bed. The
tools, instead of being held by shanks inserted in holes in the turret,
are designed so that they can be clamped firmly onto the low circular
turret plate.

An interesting example of flat turret lathe work is shown in Fig. 22.
This is