2.2 Precaution of usage for Bevel gear
① To obtain ideal engagement of the Bevel gears, the correct shaft angle and proper backlash is necessary when assembling.
② For Bevel gear, it is important to note method of installation. Bearing for the shaft for Bevel gear is mainly on oneside. Therefore shaft becomes defective due to deflection when load is applied. Single contact occurs and resultsin overhung condition.
The design of gear axes and bearings should be firm and provide bearing as close as possible to Bevel gear.
During assembly, shift the non-fixed Bevel gear up and down in axis direction to obtain proper tooth bearing. It isrecommended to put shim at area of base surface for adjustment of tooth bearing.
③ We recommend that Machined straight bevel gears are suitable for circumferential speed (pitch diameter) lessthan 328m/min and Machined spiral bevel gears are suitable for circumferential speed (pitch diameter) more than
328m/min. The above-mentioned statement does not apply to Injection molded type of Bevel gears.
The Gleason Company in USA recommend that Machined spiral bevel gears are suitable for circumferential speed(pitch diameter) more than 5.5 m/s and above 1,000 revolution per minute and Ground spiral bevel gear are suitable for circumferential speed (pitch diameter) more than 40 m/s.
④ Spiral bevel gears are able to run smoothly in high speed environment providing a quiet operation due to fewer
Number of teeth contacting with mated gear and wide Number of teeth on Pitch cone as compared to Straightbevel gear.
Spiral bevel gear has overlapping engagement on Pitch cone surface element between tooth to tooth and theload does not concentrate on one (1) Tooth tip. The advantages are extremely steady and compact design for usage at high speed.
The only disadvantage is axial thrust load, which is generated due to Spiral tooth trace. Therefore proper designof the bearing location with firm support is needed to be as close to the Spiral bevel gear as possible in order tominimize this Axial thrust load. (Refer to Fig. 3)

Thrust ofdrivenRight
hand
Thrust ofdriven

Right
hand

Left
hand
Left
hand

Thrust ofDriverRevolving
direction
Thrust ofdrivenLefthand
Thrust ofdrivenRight
hand

Thrust ofDriver
Revolving
direction

Thrust ofDriverRevolving
direction
Left
handRight
hand

Thrust ofDriverRevolving
direction

Fig. 3 Thrust load on Spiral bevel gear43

⑤ The load applied to Straight bevel gear (Refer toFig. 4)(a) Tangential load

Fn1.432 H × 106
(kgf)
F=dmn

Ft

Fa Ft
FsF

dmHereby
H : Transfer power (PS)n : Revolution per minute (rpm)dm : Mean pitch diameter (mm)Fig. 4(b) Thrust in Axial direction
Fα = F tan αsinδ (kgf)
Herebyα : Pressure angle
δ : Pitch angle(b) When convex side is driver(b.1) Thrust in axial direction
Driving gear(c) Calculation for load to displace the axis
Fs = F tanα cosį (kgf)(d)Normal loadFn =§ sinδ ·Fa = F {tanα ¨¸ + tanβ cosδ } • 9.80665 [N]© cosβ ¹
Herebyα :Pressure angle
δ :Pitch angle
β : Spiral angleF(kgf)
cosα(a)Fv

A

FtFn(b)F§ sinδ ·Fa = F {tanα ¨¸ − tanβ cosδ } • 9.80665 [N]© cosβ ¹
Driven gear

BFV
Fv(a)

Refer to Fig. 5, when the condition is Fa>0, axial thrust
direction is away from the top. The condition is Fa<0,axis thrust direction is towards the top.
Generally, pinion has smaller pitch angle δ due toFa<0. Stable design to convex side is necessary.
(b.2) Calculation for load to displace the axis

Ft

§ cosδ ·Fs = F {tanα ¨¸ + tanβ sinδ } (kgf) • 9.80665 [N]© cosβ ¹(b.3) Normal load

Fs

Fn =FuFaFcosβ cosα

Fig. 5(c) When concave side is driver.
When the load is applied to flank, Fu direction is opposite from drawing,⑥ The load applied to Spiral bevel gear. (Refer to Fig. 5)(a)Tangential load(c.1) Thrust to axial direction (direction away from the top)
Driving gearF=

1.432 H × 106
dmnHereby
H : Transfer power (PS)n : Revolution per minute (rpm)dm : Mean pitch diameter (mm)§ sinδ ·Fa = F {tanα ¨¸ + tanβ cosδ } • 9.80665 [N]© cosβ ¹
Driven gear§ sinδ ·Fa = F {tanα ¨¸ − tanβ cosδ } • 9.80665 [N]© cosβ ¹(c.2) Calculation for load to displace the axis
§ cosδ ·Fs = F {tanα ¨¸ − tanβ sinδ } • 9.80665 [N]© cosβ ¹44