I center workpieces in a lathe using a device made from an old roller bearing pressed on the end of a shaft. I attach the shaft to the machine's turret tool post and lightly clamp the workpiece in a self-centering chuck.
In operation, I run the lathe at slow speeds and advance the cross-slide until the roller bearing contacts the workpiece. As I continually move in the cross-slide, the workpiece begins running true. At this point, I stop the lathe and fully tighten the chuck.
Making hobs a new set of teeth
My idea converts a gear hob's trapezoidal teeth profiles (in inches) to other profiles with the same diametric pitch and distance between teeth.
I work with three groups of hobs. The A-group consists of gear hobs with 14.5°, 20°, and 25° teeth profiles that I convert into any angle (six versions) for involute gears. In the B-group, I convert spline-shaft hobs with 30°, 37.5°, and 45° (for involute spline shafts) to six versions, and in the C-group, I convert between any angle of trapezoidal teeth profiles in groups A and B (18 versions).
For fixed pitch, I can grind any hob angle from five other hob angles if necessary. I grind the hob teeth O.D.s and I.D.s and relieve them using an abrasive disk with the corresponding angle.
A computer program, algorithms, and tables show that when converting in the A-group (gear hobs) expediency starts at pitch 4 and goes to pitch 48. In the B-group, it runs from pitch 10 to pitch 48 for any hob's tooth angle. But converting a 37.5° tooth to 30° and vice versa starts at pitch 6 to pitch 48 (spline-shaft hobs). Converting in the C-group (gear hobs and spline-shaft hobs), expediency runs from pitch 10 to pitch 48 for any angle, but only for converting 37.5° to 20° and 25°. Converting 30° to 20° and 25° starts at pitch 6 and runs to pitch 48.
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Winner for June 2004: Roger Schicker,"Getting an angle on screw cutoff," p. 64