[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.