Base tangent length (with allowance)
| Symbol | Wk |
|---|---|
| Unit | mm |
| Attribute-ID | span measurement |
| Numeric ID | 810 |
| Value Type | PMTechValue |
For external gears, the base tangent length Wk is the distance measured across k teeth between two parallel planes. The planes will each touch a right and left flank in the involute part of the tooth flanks.
The number of teeth measured k should be chosen so that the measuring planes touch the tooth flanks near the center of the tooth height. The minimum number of teeth measured is 2, as k = 1 would mean the measurement would be close to the base circle. Specification of the base tangent width Wk with number of teeth measured applies to the finished gear (actual test dimension).
The base tangent length Wk and number of teeth measured k are used to determine the section of the involute in which the flank area lies. Therefore, they can be given as an alternative to the addendum modification coefficient or other test dimensions.