Rolling to center

Rolling to center

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.

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.

Noshir Kapadia
Thane, India


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.

Mark Grizotsky
Willowdale, Ont.

Pick the winning Practical Idea!

Select the best Practical Idea in this issue by circling the associated number on the reader service card. Winners receive an award of $100. An honorarium is paid for each item published in this column. Submitted ideas are subject to editing, and sketches will be drawn to conform to AM's style and format. Submission of clear, close-up photos is encouraged.

Send material to Practical Ideas, AMERICAN MACHINIST, Penton Media Inc., 1300 E. 9th St., Cleveland, OH 44114-1503. Please include your name, address, zip code, and Social Security number.

Winner for June 2004: Roger Schicker,"Getting an angle on screw cutoff," p. 64

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