Addendum modification coeff.

With the addendum modification coefficient, a specific modification of the tooth form is possible 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 x_hm1 = - x_hm2. A positive addendum modification coefficient increases the height of the tooth tip and simultaneously reduces the height of the tooth root. Thus, if the positive addendum modification is too large, pointed teeth can be produced, and with increasing negative addendum modification the tendency to undercut increases. The addendum modification coefficient refers to the middle normal module.

The addendum modification x_hm

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m_mn 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.

Relations between type I data (European Standards) and type II data (AGMA)

$x_{hm}=k_d \left(\frac{1}{2}-c_{ham}\right)$

xhm	Addendum modification coefficient (profile shift coefficient)
kd	Depth factor
cham	Mean addendum factor