2.3 Precaution of usage for Worm gear pair
① To obtain ideal engagement of Worm gear and Worm wheel’s shafts, provide right angle (90°) correctly.
② Lubricant oil is indispensable to Worm gear and Worm wheel during operation due to high friction between
flanks of Worm gear and Worm wheel.
③ Engagement of the same number of thread and hand of thread are indispensable to Worm gear and Worm wheel.
(Engage Worm gear and Worm wheel with both having right hand and one thread)④ The design of the axes between Worm gear and Worm wheel should be firm and provide bearing as close as possible to Worm gear pair.
⑤ Provide the bearing that will completely support the Worm gear pair as the axial thrust increases during operation. Refer to Fig. 6 for axial thrust direction.

Right hand Worm gear

DriverThrust bearing

DriverLeft hand Worm gear

DriverThrust bearing

DriverFig. 6 Axial thrust load to Worm gear and location of bearings.

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⑥ W hen assembling and warm up for Worm gear
pair, design such that Tooth contact can be measured and assembly position can be adjusted.
⑦ Worm gear pair performs self-locking when leadangle is below 4 ° . Please separately design thesafety device to stop the gear from inversing.
⑧ Load applied to Worm gear pair (Refer to Fig. 7)	F1d1/2 is moment for driver of Worm gear. F2 is revolving force for Worm wheel by F1d1/2. Formula isas follows,
4.5H × 106• 9.80665 (N)F 1 = F 2 tan(Ȗ + ȡ) =
ʌd 1n1(a) F2 is axial direction thrust for Worm gear.
F2 =F11.432 H × 10
• 9.80665 (N)=tan(Ȗ + ȡ) tan(Ȗ + ȡ) × d 1n16F1 is axial direction thrust for Worm wheel.
1.432 H × 106• 9.80665 (N)( d 1n1)F1 =Hereby
H : Net power applied to Worm gear  (PS=horse power)
γ : Lead angletanρ =µcos α n

μ : Coefficient of friction on flank
α n : Normal pressure angle
d1 : Pitch diameter of Worm gear (mm)n1 : Revolution speed per minute for Worm gear
ρ : Apparent friction angle of flank
Note: If H2PS is the power from Worm wheel and η R isefficiency. Calculation is as follows.  
H=H2ȘRBasic formula of Worm gear pair
1. Sliding velocity υ s(m/s)υs =πd 1n160 × 1000 × cosγ

Herebyd1 : Pitch diameter of Worm gear (mm)n1 : Revolution per minute for Worm gear (min-1)
γ : Reference pitch cylinder lead angle (°)
2. Torque and Efficiency (When the driver is fromWorm gear)
T2 =Ft d 2• 9.80665 (N • m)
2000

HerebyT2 : Nominal torque of Worm wheel (N・m)
Ft : Nominal circular force of Worm wheel (N)d2 : Pitch circumferential diameter of Worm wheel(mm)T1 =Ft d 2T2=uη R 2000uη RHereby
T1 : Nominal torque of Worm gear (N・m)u : Gear ratio (u=z2/zw)
η R : Transfer efficiency of Worm gear pair whendriver is from Worm gear.

§µ ·tanγ ¨1 − tanγ
¸cos α n ¹©
ηR =tanγ +µcos α nHerebyμ : Coefficient of friction
α n : Normal reference pressure angle (°)
Note the efficiency of KG’ s Worm gear pair is as follows.

(b) Calculation for load to displace the axis

Fs =F 1tan α n cosρ(N)sin(γ + ρ )Alternatively

Worm gear with single thread
Worm gear with double thread

45% - 55%
55% - 65%= Fnsin α n(c) Normal load
Fn =F 1cosρ(N)sin(γ + ρ )cos α nReference literature: Dr. Waguri Akira “Gear Designand Manufacturer” 30th   Machine Literary of Japan.

R
F1GF2FnFs

AnFig. 7 Load applied to Worm gear pair.

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