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21.3 Contact Conditions of Cross-Axes Helical Gears
The bottom graphic in Figure 2 shows one contact line between generating
rack and gear 1 and a second contact line between generating rack and gear
2. The contact lines are crossing under an angle and only have one common
point. This is the reason why cross-axes helical gears have point contact ra-
ther than line contact. The sum of the intersecting points of gear 1 and gear 2
define the path of contact. Only the gear pair with zero-degree shaft angle in
the top graphic has matching contact lines between gear 1, generating rack
and gear 2. Only contacting points along the theoretical path of contact in red
transmit the correct ratio.
Figure 2: Cross-axes helical gear relationships
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