The basic rack fillet radius must be reduced for teeth with a 25-degree pressure angle having a clearance in excess of 0.250/P. This should be avoided on highly loaded gears where the consequently reduced J factor will increase gear tooth stress excessively.ī A minimum clearance of 0.157/P may be used for the basic 20-degree and 25-degree pressure angle rack in the case of shallow root sections and use of existing hobs or cutters.Ĭ The fillet radius of the basic rack should not exceed 0.235/P for a 20-degree pressure angle rack or 0.270/P for a 25-degree pressure angle rack for a clearance of 0.157/P. The addendum length is the length from the pitch circle diameter of the tooth shape to the top of the tooth : ha1×m1×1. The addendum length of a general spur gear is obtained by the following formula. This is of particular importance on gears of few teeth or if the gear blank configuration requires the use of a small diameter shaper cutter, in which case the dedendum may need to be increased to as much as 1.45/P. Calculation of the addendum length, ha, and the tooth depth, h. ![]() ![]() A When gears are preshave cut on a gear shaper the dedendum will usually need to be increased to 1.40/P to allow for the higher fillet trochoid produced by the shaper cutter.
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