Page 109 - Mechanical Engineer's Data Handbook

98 MECHANICAL ENGINEER'S DATA HANDBOOK

Let: Spiral bevel gear
&=pressure angle normal to the tooth
a= helix angle Let:
a =spiral angle of pinion
Separating force F, = F, tan - (6" c$,, = normal pressure angle
cos a
tan 6, sin
Axial force Fa = F, tan a Force on pinion F, = F, k tan a cosg 1
[ cosa
Double helical gears tan cos B -
Force on gear F,= F, +tan a sin 1
[ cosa
To eliminate the axial thrust, gears have two sections
with helices of opposite hand. These are also called
'herringbone gears'.
- @

1
-
-
3

Single helical gear

For the diagram shown the signs are '+' for F, and
'-' for F,. The signs are reversed if the hand of the
. . helix is reversed or the speed is reversed; they remain
the same if both are reversed.

Double helical gear

2.10.5 Bevel gears

Straight bevel gears
Let:
4 =pressure angle of teeth right bevel gear
B = pinion pitch cone angle I '~
Tangential force on gears = F,
Separating force F, = F, tan (b
Pinion thrust F, = F, sin B
Gear thrust F, = F, cos fl
,,' p,

Spiral bevel gear