This standard is applicable to external spur and
helical gears with diametral pitch of 20 through 120
(1.25 through 0.2 module) and a profile angle of 20
degrees.
It only applies to standard gears with 24 teeth or
more; enlarged pinions with 9 through 23 teeth; and
reduced gears.
Much of this same information is applicable to internal
gears.
1 .I Tooth proportions
The tooth proportions shown herein may be usedfor
many gear designs of finer than 120 diametral pitch
(0.2 module); however, such designs should be
checked for suitability, particularly in the areas of
contact ratio, undercutting, and clearance.
The spur gear portions of this standard closely follow
AGMA 201.02, Tooth Proportions for Coarse-
Pitch Involute Spur Gears.
The main difference between the proportions of
fine-pitch gears and those of the coarse-pitch is in
the clearance. In fine-pitch gearing, wear on the
points of the cutting tools is proportionally greater
than in coarse-pitch tools. The fillet radius produced
by such tooling will therefore be proportionally
greater. The increased clearance in gearing of
20 diametral pitch (1.25 module) and finer provides
both for the relatively larger fillet and also for foreign
material that tends to accumulate at the bottoms of
the teeth.
1.2 Number of teeth
Gear designs with low numbers of teeth should be
checked for suitabilify, particularly in the areas of
contact ratio, undercutting, and clearance, as well
as for strength and durability for load and life considerations.