To prevent chipping at a tooth top of a latter half coast side of a chamfer tooth part of a form rolling flat die so as to extend a life.
In the form rolling flat die 1 constituting of the chamfer tooth part 10, an adjusting tooth part 20, a finish tooth part 6, a relief tooth part 15 for working an involute spline, a round radius R1 of a corner 2a of a coast side of a front chamfer tooth part 2 is below a corner radius R2 of a rear side chamfer tooth part 3, the corner radius R2 of a rear side chamfer tooth part is larger than or equal to a coast radius R3 of a front adjusting tooth part, a corner radius R4 of a rear adjusting tooth part is below a corner radius R3 of the front adjusting tooth part, a corner radius R5 of the finish tooth part is equal to a round radius R6 of a tooth root of a work. Further, it is preferable to set as R1<R6, R2>R1+(0.1-0.3) module, R3>R1+0.1-0.3 module, R4=R5=R6.
KUMAGAI TAKAHIRO
SUMIYA SOICHI
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