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Screw Gears: Technical Information

Characteristics∧ top

KHK stock screw gears come in modules 1 ~ 4, 10 to 30 teeth, and four materials: S45C, SUS303, CAC702 (formerly A BC2) and MC nylon.

Catalog No. Module Material Heat
JIS B 1702-1 : 1998
SN 1 ~ 4 S45C Cut N9 Possible Popular screw gears. Additionally, gear tooth induction hardening secondary operations can be performed.
SUN 1 ~ 3 SUS303 Cut N9 Possible Suitable for food machinery due to SUS303's rust-resistant qualities.
AN 1 ~ 4 CAC702
(Al BC2)
Cut N9 Possible made of aluminum bronze, these gears have excellent wear resistance.
PN 1.5 ~ 3 MC901 Cut N9 Possible Light-weight products made of MC Nylon and can be used without lubrication.

Selection Hints∧ top

Please select the most suitable products by carefully considering the characteristics of items and contents of the product tables. It is also important to read all applicable “CAUTION” notes before the final selection. Since screw gears come in right- or left-hand helix, make sure to include the letter "R" or "L" in the catalog number when you order.

1. Caution in Selecting the Mating Gears
Screw gears are used for offset shafts. Whether the shafts are paralleled offset or skewed offset depends on the helix hands of the mating gears.

Direction of Shaft Arrangement of Helix Hands
Skewed Shafts RH-RH or LH-LH
Parallel Shafts RH-LH

Arrangements of helix hands of screw gears

Trusted Quality Achieved by Years of Experience.
Efficient production by lapping cutting processes
Gear Cutting by a Hobbing MachineGear cutting by a hobbing machine

Application Hints∧ top

Rotation of two rollers by one input shaft
*The illustration above is a design example, not a design for machinery or a device in actual use.

2. Caution in Selecting Gears Based on Gear Strength
The allowable surface strengths listed in the product pages were derived using the Niemann formula as reference values (for the case of skewed offset shafts).

There is scarce amount of data on the strength of screw gears. The values of constant K0 used in the calculations, which depend on the material of the mating gears, are our estimates. The mathematical expression below shows the Niemann formula to determine allowable tangential force F t (kgf) and allowable torque T (kgf • m) on a basic circle.

The Niemann Formula
Niemann Formula

Value of fz

Z2 Z1
10 13 15 20 26 30
10 1.538          
13 2.005 1.538        
15 2.279 1.786 1.538      
20 2.963 2.329 2.053 1.538    
26 3.695 2.963 2.588 2.005 1.538  
30 4.161 3.350 2.963 2.279 1.786 1.538

K0 values depending on material combination

K0 The maximum
allowable sliding speed m/s
No. of teeth
of mating gears
SN 0.0030 2.5 Same
of Teeth
100 rpm
SN 0.0030
(Note 1)
(Note 1)
SN 0.0050 5
PN SN 0.0030
(Note 1)
(Note 1)

(Note 1) K0 values and the maximum allowable sliding speed of SUN and PN products are set by KHK. Screw gears are typically used with lubrication. In case of using PN products without lubrication, the parenthetical values shown in the table are applied.

Application Examples Application Hints:
In order to use KHK stock screw gears safely, read the Application Hints carefully before proceeding. Also, please refer to the "Application Hints" in the technical information section on KHK stock spur gears, when performing secondary operations.

1. Points of Caution in Assembling
KHK stock screw gears are designed to give the proper backlash when assembled using the center distance given by the formula below with a tolerance of H7 to H8. The amount of backlash is given in the product table for each gear.

Backlash Screw Gears
(Caution) PN Plastic Screw Gears are excluded.

Due to their helix, screw gears produce axial thrust forces. The bearings must be selected properly to be able to handle these thrust forces. The directions of thrust change with the hand of helix and the direction os rotation as illustrated below.

Direction of Rotation and Thrust Force
Direction of Rotation and Thrust Force
(Caution) For parallel shaft applications, see the "Application Hints" for KHK Helical Gears.
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