GROUND FORM FINISHING HOBS

THIS paper covers some of the more important points in the manufacture and care of hobs. The differences in manufacture and application between machine-relieved and relief-ground hobs are pointed out clearly. Emphasis is placed on the relief-ground type, recommended for use for gears where silent running, most exact uniformity of rotation, or close fitting is required.

The author gives special attention to the elements that must be watched in order to maintain accuracy; the care that must be taken in sharpening hobs, as well as in mounting them on the hobbing machine for cutting gears; and the importance of accuracy in hobbing machines and in gear blanks, for quiet and efficient gears.

Among the various testing instruments described that indicate how closely the finished hob approaches the ideal conditions, are a lead-testing machine and a contour-testing fixture. A chart is presented for use in estimating gear-cutting time.