ABSTRACT
In traditional gear design the preselected basic or generating rack param eters and addendum modification or X-shift factor define the nominal involute gear geometry. X-shift factor selection for the given pair of gears is limited by the block contour (Figure 1.5). Borders of the block contour include the undercut isograms, the interference isograms, the minimum contact ratio (equal to 1.0 for spur gears) isogram, and the isograms of the minimum tooth tip thickness to exclude the gears with the pointed tooth tips. If a block contour of some generating rack does not contain an optimal gear geometry for a particular gear application, the generating rack parameters (pressure angle, addendum, whole depth proportions, etc.) should be changed. Then the altered rack block contour may include the desired optimal gear geometry.
