Tooth Proportions for Fine- Pitch Spur and Helical Gearing
|Publication Date:||1 January 2007|
This standard is applicable to external spur and helical gears with diametral pitch of 20 through 120 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 for meshing with enlarged pinions at standard center distances.
Much of this same information is applicable to internal gears.
The tooth proportions shown hereinmay be used for many gear designs of finer than 120 diametral pitch; however, such designs should be checked for suitability, particularly in the areas of contact ratio, undercutting, and clearance.
This standard is similar to ISO 53, Cylindrical gears for general and heavy engineering - Standard basic rack tooth profile.
The main difference between the proportions of fine-pitch gears and those of 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 and finer provides both for the relatively larger fillet and also for foreign material that tends to accumulate at the bottoms of the teeth.
Number of teeth
Gear designs with low numbers of teeth should be checked for suitability, particularly in the areas of contact ratio, undercutting, and clearance, as well as for strength and durability for load and life considerations.