Addendum modification coeff.
| Symbol | xhm |
|---|---|
| Unit | - |
| Attribute-ID | addendum modification coefficient |
| Numeric ID | 359 |
| Value Type | PMDouble |
The addendum modification coefficient makes it possible to design a targeted modification to the tooth form in order to avoid undercut or pointed tooth tips, or to influence the tooth load capacity. Bevel gears are designed as V-zero gears; i.e., the sum of the addendum modification coefficients is equal to 0 or xhm1 = - xhm2. A positive addendum modification coefficient increases the height of the tooth tip and simultaneously reduces the height of the tooth root.
Pointed teeth can be produced if the positive addendum modification is too large, and the tendency toward undercut increases with negative addendum modifications. The addendum modification coefficient refers to the middle normal module.
The addendum modification xhm·mmn is the shallower or deeper path in millimeters created by the tool.
| 1 | Tooth profile with profile shift and thickness modification |
| 2 | Reference line |
| 3 | Basic rack tooth profile |
| xhm | Addendum modification coefficient (profile shift coefficient) |
| mmn | Mean normal module |
For more information, see ISO 23509, section 7. (Name: profile shift coefficient)
Positive addendum modification:
Profile reference line shifted from the reference circle in the direction of the tip circle
Negative addendum modification:
Profile reference line shifted from the reference circle in the direction of the root circle.
Effects of positive addendum modification:
- Undercut is reduced or eliminated
- Minimum number of teeth is reduced
- Tooth root becomes thicker
- Tooth root fillet radius is reduced
Negative addendum modifications lead to the opposite results.