T-60
Standard screw gears have relations as follows:
dw1 = d1, dw2 = d2
ü
ý
(7-7)
bw1 = b1, bw2 = b2
þ
7.3 Axial Thrust Of Helical Gears
In both parallel-shaft and crossed-shaft applications, helical gears develop an axial
thrust load. This is a useless force that loads gear teeth and bearings and must accordingly
be considered in the housing and bearing design. In some special instrument designs,
this thrust load can be utilized to actuate face clutches, provide a friction drag, or other
special purpose. The magnitude of the thrust load depends on the helix angle and is given
by the expression:
WT = W t tanb
(7-8)
where
WT = axial thrust load, and
W t = transmitted load.
The direction of the thrust load is related to the hand of the gear and the direction of
rotation. This is depicted in Figure 7-1. When the helix angle is larger than about 20°,
the use of double helical gears with opposite hands (Figure 7-3a) or herringbone gears
(Figure 7-3b) is worth considering.
Figure 7-3a
Figure 7-3b
More detail on thrust force of helical gears is presented in SECTION 16.
SECTION 8 BEVEL GEARING
For intersecting shafts, bevel gears offer
a good means of transmitting motion and
power. Most transmissions occur at right
angles, Figure 8-1, but the shaft angle can
be any value. Ratios up to 4:1 are common,
although higher ratios are possible as well.
Fig. 8-1
Typical Right Angle
Bevel Gear
