Gear Rack – creation of linear motion

Gear racks are utilized to convert rotating movement into linear motion. A gear rack has straight teeth cut into one surface of a square or round section rod and operates with a pinion, which is a small cylindrical gear meshing with the gear rack. Generally, gear rack and pinion are collectively called “rack and pinion”. There are many ways to use gears. For example, as shown in the picture, a gear is used with the gear rack to rotate a parallel shaft.

To provide many variation of rack and pinion, KHK has many types of gear racks in stock. If the application requires a long length requiring multiple gear racks in series, we have racks with the tooth forms correctly configured at the ends. These are described as “gear racks with machined ends”. When a gear rack is produced, the teeth cutting process and heat treatment can cause it to try & go out of true. We can control this with special presses & remedial processes.

There are applications where the gear rack is stationary, while the pinion traverses and others where the pinion rotates on a fixed axis while the gear rack moves. The former is used widely in conveying systems while the latter can be used in extrusion systems and lifting/lowering applications.

As a mechanical element to transfer rotary into linear motion, gear racks are often compared to ball screws. There are pros and cons. The advantages of a gear rack is its mechanical simplicity, large load carrying capacity, no limit to the length, etc. One disadvantage though is the backlash. The advantage of a ball screw is the high precision and lower backlash while the shortcomings include the limit in length due to deflection.

Rack and pinions are used for lifting mechanisms (vertical movement), horizontal movement, positioning mechanisms, stoppers and the synchronous rotation of several shafts in general industrial machinery. On the other hand, they are also used in steering systems to change the direction of cars. The characteristics of rack and pinion systems in steering are as follows: simple structure, high rigidity, small and lightweight, and excellent responsiveness. With this mechanism, the pinion, mounted to the steering shaft, is meshed with a steering rack to transmit rotary motion laterlly (converting it to linear motion) so that you can control the wheel. In addition, rack and pinions are used for various purposes, such as toys and lateral slide gates.

gear rack selector button

Related links :
“Raw Material” and “Gear Precision Grade” Equivalent Tables
齿条
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What is a rack and pinion ?

A rack and pinion are used when converting rotational movement to linear motion (or vice versa). A bar shaped gear with an infinite (flat surface) radius of a cylindrical gear is called a rack, and a meshed spur gear is called a pinion. A rack can be used by extending it combining as many racks with machining operation on the end faces when necessary. A helical rack is a bar shaped gear with slanted linear tooth trace that is used when silence and high speed rotation are required, and it can be meshed with a helical gear.

various racks
Image : Plastic / Steel racks

Materials and heat treating racks and pinions

As for the materials of a racks and pinions, strength, abrasion resistance, and absorbency are considered.
With steel, S45C (1045 in AISI/SAE, C45 in ISO, equivalent to C 45K in DIN), SCM440 (4140 in AISI/SAE, equivalent to 42CrMo4V in ISO and DIN), 16MnCr5 (name in ISO, equivalent to 17Cr3 in DIN), with stainless steel, SUS303 (303/S30300 in AISI/SAE, 13 in ISO, equivalent to X10CrNiS18-9 in DIN), SUS304 (304/S30400 in AISI/SAE, 6 in ISO, equivalent to X5CrNi18-10 in DIN), with plastic material, reinforced nylon called engineering plastic, polyacetal (equivalent to Duracon and POM), polyamide, are used.
Regarding the heat treatment of a rack and pinion, thermal refining, carburizing and quenching, tooth face high frequency hardening, and tooth face laser hardening are used depending on the kinds of materials and purposes.

material of racks
Image : Material of racks

Overall length and cross-sectional shape of a rack

The overall length of standard racks on the market is generally not more than 2000mm, and offered in 500mm units such as 500mm, 1000mm, 1500mm.
Furthermore, the cross-sectional shape is often a square or rectangle, and some are round called round rack type.

cross section of racks
Image : Cross sectional shape of racks

Production of racks and pinions

Although the difficulty in production varies depending on the accuracy classes and specifications, the basic production of the rack and pinion is possible with a rack cutting machine and gear hobbing machine. They are produced by many gear manufacturers and rack specialized manufacturers in the world. They are especially produced on a large scale by famous rack manufacturers in Germany and Taiwan.

Using Racks and Pinions

The rack and pinion are used mainly for carrier devices, steering gear mechanisms for vehicles, machine tools, lifting apparatus, and printing machines.
When attaching a rack to a machine, mounting holes drilled though the bottom or through the side are frequently used, additional methods include counterbored bolt holes and tapped holes.

usage of rack
Image : Rack and pinion used for manual lifting device

The helix angle of helical rack

The helix angle of a helical rack is set at 19 degrees 31’42” by many rack manufacturers. When the helix angle is set like so, the movement when a pinion rotates (for instance one rotation) becomes an exact distance in mm, thus making it user-friendly.

helix-angle of helical rack
Image : Helical rack

Lubricating Racks and Pinions

As for the lubrication of a rack and pinion, there are several methods used.
One such lubrication system consists of a lubricating device (main body), a tube to deliver the lubricant, a check valve and a special urethane pinion at the end of the tube.
The rack and pinion in this system are lubricated as the lubricant is dispered by the pinion.
Since the pinion injects the lubricant into the mesh as it rotates across the gear rack, the pitch of the rack must be the same as the module of the pinion, and in the case of helical rack and pinions, the rack and pinion must be of the same helix angle and opposite in direction.

pinion for lubrication of rack
Image : Pinion made of urethane

Comparison between racks and pinions and ball screws

As a mechanical element that produces linear motion, a rack and pinion system is often compared with to ball screw.
When compared with a rack and pinion, generally a ball screw has superiorities of accurate positioning, smooth motion with a little friction, and no backlash, on the other hand, ball screws have the disadvantages of higher cost, the difficulty of producing ball screws with long lengths due to deflexion, and unsuitability for heavy loads.

ball screw
Image : Ball screw in machine tool

CP Racks & Pinions – Facilitates positioning in linear motion applications –

By adopting CP (circular pitch) racks and pinions, the travel distance with one rotation of pinion becomes an integer number. This improves the user’s convenience. For example, if the pitch of the pinion is CP5 (pitch is 5mm) and if the number of teeth is 20, then when the pinion rotates once, the distance traveled becomes exactly 100mm.

It has been listed elsewhere, but there are three international standards of gear pitches: module, inch standard of DP and above mentioned CP. The following link will lead to the comparison of these pitches :
Table of Comparative Gear Pitch
There is no interchangeability between pinion and rack if different pitch systems are used in the pair.

In addition, KHK offers tapered racks and pinions. These are produced by angling each tooth of the rack and pinion. Conventionally, in order to adjust the backlash, it was necessary to change the distance between the rack and the axis of the pinion. But with tapered rack and pinion, this difficult task can be easily accomplished by simply shifting the pinion in its axial direction. Because of the taper in the teeth, they are not interchangeable with regular rack and pinion.

Technical Information of CP Racks & Pinions

Characteristics

KHK stock CP racks and pinions are suitable in applications where very accurate positioning in linear motion is required. For your convenience, we offer circular pitches of 2.5 to 20 mm and in lengths of 100 to 2000 mm. (FRCP is available to 4000 mm)

Movement of one cycle of the CP10-30 pinion on a CP rack vs.SS3-30 (m3) on a m3 rack.
Movement of one cycle of the CP10 30 pinion on a CP rack vs.SS3 30 (m3) on a m3 rack

About CP Racks & Pinions

The reference pitch of a metric module is computed by multiplying the number of module by π (3.14159). For example, the reference pitch of m 3 rack is 9.425 mm (3 * π). When using a rack and a pinion in a linear motion application, the fact that the pitch is not an integral number presents a difficulty in accurate positioning. This problem is solved by CP racks and pinions where one rotation of a pinion moves it precisely 50, 100, 150, … or 600 mm. The following table lists the main features. The following table lists the main features.

Racks

  • Catalog No. Note 1 : STRCPF / STRCPFD
    Pitch (mm) : 5, 10
    Total Length (mm) : 1000
    Material : S45C
    Heat Treatment : –
    Tooth Surface Finish : Cut
    Precision KHK R 001 : 4
    Features : By pairing with KTSCP pinion, the backlash may be adjusted.
  • Catalog No. Note 1 : MRGCPF / MRGCPFD
    Pitch (mm) : 1.5-3
    Total Length (mm) : 500
    Material : SCM415
    Heat Treatment : Tooth area Carburized
    Tooth Surface Finish : Ground
    Precision KHK R 001 : 1
    Features : Has the highest strength and precision in the KHK standard rack series. Bolt holes can be remachined as carburizing is applied only within the tooth area. J Series products are also available.
  • Catalog No. Note 1 : KRGCPF – H / KRGCPFD – H
    Pitch (mm) : 5, 10
    Total Length (mm) : 500, 1000
    Material : SCM440
    Heat Treatment : Thermal refined, teeth induction hardened
    Tooth Surface Finish : Ground
    Precision KHK R 001 : 1
    Features : Heat treated ground gears with high precision and strength has excellent cost-performance ratio. J Series products are also available.
  • Catalog No. Note 1 : KRGCP / KRGCPF / KRGCPD
    Pitch (mm) : 5, 10
    Total Length (mm) : 100, 500, 1000
    Material : SCM440
    Heat Treatment : Thermal Refined
    Tooth Surface Finish : Ground
    Precision KHK R 001 : 1
    Features : High strength and abrasion-resistant for precision linear motion.
  • Catalog No. Note 1 : SRGCP / SRGCPF / SRGCPFD
    Pitch (mm) : 5, 10, 15, 20
    Total Length (mm) : 100, 500, 1000
    Material : S45C
    Heat Treatment : Gear teeth induction hardened
    Tooth Surface Finish : Ground
    Precision KHK R 001 : 3
    Features : Reasonably priced ground racks with abrasion-resistant characteristics. J Series products are also available.
  • Catalog No. Note 1 : KRCPF-H / KRCPFD-H
    Pitch (mm) : 5, 10
    Total Length (mm) : 1000
    Material : SCM440
    Heat Treatment : Thermal refined, teeth induction hardened
    Tooth Surface Finish : Cut
    Precision KHK R 001 : 5
    Features : This is a strong rack made of Chromoly steel, treated by carburizing. Has high-strength, high wear resistance, and enables downsizing of SR racks. J Series products are also available.
  • Catalog No. Note 1 : SRCPF-H / SRCPFD-H
    Pitch (mm) : 5, 10, 15, 20
    Total Length (mm) : 1000
    Material : S45C
    Heat Treatment : –
    Tooth Surface Finish : Cut
    Precision KHK R 001 : 5
    Features : Stable Hardened racks with high strength, long life span are reasonably priced. J Series products are also available.
  • Catalog No. Note 1 : SRCPF-H / SRCPFD-H
    Pitch (mm) : 5, 10, 15, 20
    Total Length (mm) : 1000
    Material : S45C
    Heat Treatment : –
    Tooth Surface Finish : Cut
    Precision KHK R 001 : 5
    Features : Stable Hardened racks with high strength, long life span are reasonably priced. J Series products are also available.
  • Catalog No. Note 1 : KRCPF  /  KRCPFD
    Pitch (mm) : 5, 10
    Total Length (mm) : 1000
    Material : SCM440
    Heat Treatment : Thermal Refined
    Tooth Surface Finish : Cut
    Precision KHK R 001 : 4
    Features : Increased strength with SCM440 material which is thermal refined.
  • Catalog No. Note 1 : SRCP / SRCPF / SRCPFD / SRCPFK
    Pitch (mm) : 2.5, 5, 10, 15, 20
    Total Length (mm) : 100, 500, 1000, 1500, 2000
    Material : S45C
    Heat Treatment : –
    Tooth Surface Finish : Cut
    Precision KHK R 001 : 4
    Features : Widely applicable due to low cost and large selection of pitches and lengths.
  • Catalog No. Note 1 : SURCPF / SURCPFD
    Pitch (mm) : 5, 10
    Total Length (mm) : 500, 1000
    Material : SUS304
    Heat Treatment : Solution treated
    Tooth Surface Finish : Cut
    Precision KHK R 001 : 5
    Features : Suitable for food machinery due to SUS304 material’s rust-resistant quality.
  • Catalog No. Note 1 : SROCP
    Pitch (mm) : 2.5, 5, 10
    Total Length (mm) : 500
    Material : S45C
    Heat Treatment : –
    Tooth Surface Finish : Cut
    Precision KHK R 001 : 4
    Features : Convenient in applications where the rack has reciprocal motion.
  • Catalog No. Note 1 : FRCP
    Pitch (mm) : 5
    Total Length (mm) : 2000, 3000, 4000
    Material : SS400
    Heat Treatment : –
    Tooth Surface Finish : Cut
    Precision KHK R 001 : 8
    Features : Cut continuously. Long length and bendable to a contour.

 

Pinions

  • Catalog No. Note 1 : KTSCP
    Pitch (mm) : 5, 10
    Number of teeth : 20-40
    Material : SCM440
    Heat Treatment : Thermal refined
    Tooth Surface Finish : Cut
    Precision JIS B 1702-1 : N8
    Features : By pairing with STRCPF rack, the backlash may be adjusted.
  • Catalog No. Note 1 : MSCPG
    Pitch (mm) : 5, 10
    Number of teeth : 20-40
    Material : SCM415
    Heat Treatment : Overall carburizing
    Tooth Surface Finish : Ground
    Precision JIS B 1702-1 : N5
    Features : Designed with positive partial transposition and to have an integral value (mm) for the mounting distance, so both strength and usability are enhanced.
  • Catalog No. Note 1 : MSCPG
    Pitch (mm) : 5, 10
    Number of teeth : 20-40
    Material : SCM415
    Heat Treatment : Overall carburizing
    Tooth Surface Finish : Ground
    Precision JIS B 1702-1 : N5
    Features : Designed with positive partial transposition and to have an integral value (mm) for the mounting distance, so both strength and usability are enhanced.
  • Catalog No. Note 1 : SSCPGS
    Pitch (mm) : 5, 10
    Number of teeth : 10-25
    Material : S45C
    Heat Treatment : Thermal refined, teeth induction hardened
    Tooth Surface Finish : Ground
    Precision JIS B 1702-1 : N7
    Features : Ground Spur Gears with Pinions, can be directly assembled with the shaft bearing, by modifying the pinion.
  • Catalog No. Note 1 : SSCPG
    Pitch (mm) : 5, 10, 15, 20
    Number of teeth : 20-40
    Material : S45C
    Heat Treatment : Gear teeth induction hardened
    Tooth Surface Finish : Ground
    Precision JIS B 1702-1 : N7
    Features : Perform secondary operations to suit your requirement on these ground CP spur gears.
  • Catalog No. Note 1 : KSCP
    Pitch (mm) : 5, 10
    Number of teeth : 20-40
    Material : SCM440
    Heat Treatment : Thermal refined, teeth induction hardened
    Tooth Surface Finish : Cut
    Precision JIS B 1702-1 : N9
    Features : Thermal refined and tooth-hardened chromoly racks, excellent in abrasion resistance. Use as mating pinions for KRCPF(-H) Racks.
  • Catalog No. Note 1 : SSCP
    Pitch (mm) : 2.5, 5, 10, 15, 20
    Number of teeth : 20-40
    Material : S45C
    Heat Treatment : –
    Tooth Surface Finish : Cut
    Precision JIS B 1702-1 : N8
    Features : Low cost and widely applicable, with a large selection of pitches and numbers of teeth.
  • Catalog No. Note 1 : SUSCP
    Pitch (mm) : 5, 10
    Number of teeth : 20-30
    Material : SUS303
    Heat Treatment : –
    Tooth Surface Finish : Cut
    Precision JIS B 1702-1 : N8
    Features : Suitable for food machinery due to SUS303 material’s rust-resistant quality.

[NOTE 1] The catalog numbers in the above tables with a suffix of F have both ends machined so that they can be butted against each other to make any desired length. The items with (D) have mounting screw holes for easier assembly.

For safer handling and to prevent damage such as deformation, KHK stock CP racks have round chamfering on the corners of the top land of the gear tooth. This rounded chamfered shape is patented by KHK. Because it is effective for reducing noise, all of KHK CP racks have this chamfering treatment.
Black colored products are KHK stock gears that have an applied black oxide coating for rust resistance; this ‘blackness’ is a product characteristic of KHK stock gears.

Selection Hints

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 notes before the final selection.

1. Caution in Selecting the Mating Gears

  1. KHK stock CP racks are mated with CP spur gears having the same pitch. Since CP2.5 (m0.796), CP5 (m1.592) and CP10 (m3.183) are very close in size to m0.8, m1.5 and m3 respectively, the selecting the proper mating gear should be verified to make sure that the items are correct. Otherwise, complications could arise.
  2. STRCPF and STRCPFD Tapered Racks are mated with KTSCP Spur Gears having the same pitch. They can also be mated with other spur gears, however, they can not be used as parallel axis gears due to the setting angles.

2. Caution in Selecting Gears Based on Gear Strength

The gear strength values shown in the product pages were computed by assuming a certain application environment. Therefore, they should be used as reference only. We recommend that each user computes his own values by applying the actual usage conditions. The table below contains the assumptions established for these products in order to compute gear strengths.

Calculation assumptions for Bending Strength

  • Catalog No. : MRGCPF / MRGCPFD
    Formula NOTE 1 : Formula of spur and helical gears on bending strength (JGMA401-01)
    No. of teeth of mating gear : 30
    Rotation : 100rpm
    Durability : Over 10^7cycles
    Impact from motor : Uniform load
    Impact from load : Uniform load
    Direction of load : Bidirectional
    Allowable bending stress at root σ Flim(kgf/mm^2) NOTE 2 : 47
    Safety factor SF : 1.2
  • Catalog No. : KRGCPF-H / KRGCPFD-H
    Formula NOTE 1 : Formula of spur and helical gears on bending strength (JGMA401-01)
    No. of teeth of mating gear : 30
    Rotation : 100rpm
    Durability : Over 10^7cycles
    Impact from motor : Uniform load
    Impact from load : Uniform load
    Direction of load : Bidirectional
    Allowable bending stress at root σ Flim(kgf/mm^2) NOTE 2 : 32
    Safety factor SF : 1.2
  • Catalog No. : KRGCP / KRGCPF / KRGCPD / KRCPF
    Formula NOTE 1 : Formula of spur and helical gears on bending strength (JGMA401-01)
    No. of teeth of mating gear : 30
    Rotation : 100rpm
    Durability : Over 10^7cycles
    Impact from motor : Uniform load
    Impact from load : Uniform load
    Direction of load : Bidirectional
    Allowable bending stress at root σ Flim(kgf/mm^2) NOTE 2 : 32
    Safety factor SF : 1.2
  • Catalog No. : SRGCP / SRGCPF / SRGCPFD
    Formula NOTE 1 : Formula of spur and helical gears on bending strength (JGMA401-01)
    No. of teeth of mating gear : 30
    Rotation : 100rpm
    Durability : Over 10^7cycles
    Impact from motor : Uniform load
    Impact from load : Uniform load
    Direction of load : Bidirectional
    Allowable bending stress at root σ Flim(kgf/mm^2) NOTE 2 : 20
    Safety factor SF : 1.2
  • Catalog No. : SRCP / SRCPF / SRCPFD / SROCP / STRCPF / STRCPFD
    Formula NOTE 1 : Formula of spur and helical gears on bending strength (JGMA401-01)
    No. of teeth of mating gear : 30
    Rotation : 100rpm
    Durability : Over 10^7cycles
    Impact from motor : Uniform load
    Impact from load : Uniform load
    Direction of load : Bidirectional
    Allowable bending stress at root σ Flim(kgf/mm^2) NOTE 2 : 20
    Safety factor SF : 1.2
  • Catalog No. : SURCPF / SURCPFD / FRCP
    Formula NOTE 1 : Formula of spur and helical gears on bending strength (JGMA401-01)
    No. of teeth of mating gear : 30
    Rotation : 100rpm
    Durability : Over 10^7cycles
    Impact from motor : Uniform load
    Impact from load : Uniform load
    Direction of load : Bidirectional
    Allowable bending stress at root σ Flim(kgf/mm^2) NOTE 2 : 10.5
    Safety factor SF : 1.2
  • Catalog No. : MSCPG
    Formula NOTE 1 : Formula of spur and helical gears on bending strength (JGMA401-01)
    No. of teeth of mating gear : Racks
    Rotation : 100rpm
    Durability : Over 10^7cycles
    Impact from motor : Uniform load
    Impact from load : Uniform load
    Direction of load : Bidirectional
    Allowable bending stress at root σ Flim(kgf/mm^2) NOTE 2 : 47
    Safety factor SF : 1.2
  • Catalog No. : SSCPGS
    Formula NOTE 1 : Formula of spur and helical gears on bending strength (JGMA401-01)
    No. of teeth of mating gear : Racks
    Rotation : 100rpm
    Durability : Over 10^7cycles
    Impact from motor : Uniform load
    Impact from load : Uniform load
    Direction of load : Bidirectional
    Allowable bending stress at root σ Flim(kgf/mm^2) NOTE 2 : 24.5
    Safety factor SF : 1.2
  • Catalog No. : SSCPG
    Formula NOTE 1 : Formula of spur and helical gears on bending strength (JGMA401-01)
    No. of teeth of mating gear : Racks
    Rotation : 100rpm
    Durability : Over 10^7cycles
    Impact from motor : Uniform load
    Impact from load : Uniform load
    Direction of load : Bidirectional
    Allowable bending stress at root σ Flim(kgf/mm^2) NOTE 2 : 19
    Safety factor SF : 1.2
  • Catalog No. : KTSCP
    Formula NOTE 1 : Formula of spur and helical gears on bending strength (JGMA401-01)
    No. of teeth of mating gear : Racks
    Rotation : 100rpm
    Durability : Over 10^7cycles
    Impact from motor : Uniform load
    Impact from load : Uniform load
    Direction of load : Bidirectional
    Allowable bending stress at root σ Flim(kgf/mm^2) NOTE 2 : 28.5
    Safety factor SF : 1.2
  • Catalog No. : KSCP
    Formula NOTE 1 : Formula of spur and helical gears on bending strength (JGMA401-01)
    No. of teeth of mating gear : Racks
    Rotation : 100rpm
    Durability : Over 10^7cycles
    Impact from motor : Uniform load
    Impact from load : Uniform load
    Direction of load : Bidirectional
    Allowable bending stress at root σ Flim(kgf/mm^2) NOTE 2 : 30
    Safety factor SF : 1.2
  • Catalog No. : SSCP
    Formula NOTE 1 : Formula of spur and helical gears on bending strength (JGMA401-01)
    No. of teeth of mating gear : Racks
    Rotation : 100rpm
    Durability : Over 10^7cycles
    Impact from motor : Uniform load
    Impact from load : Uniform load
    Direction of load : Bidirectional
    Allowable bending stress at root σ Flim(kgf/mm^2) NOTE 2 : 19
    Safety factor SF : 1.2
  • Catalog No. : SUSCP
    Formula NOTE 1 : Formula of spur and helical gears on bending strength (JGMA401-01)
    No. of teeth of mating gear : Racks
    Rotation : 100rpm
    Durability : Over 10^7cycles
    Impact from motor : Uniform load
    Impact from load : Uniform load
    Direction of load : Bidirectional
    Allowable bending stress at root σ Flim(kgf/mm^2) NOTE 2 : 10.5
    Safety factor SF : 1.2

 

Calculation assumptions for Surface Durability (Except those in common with bending strength)

  • Catalog No. : MRGCPF / MRGCPFD
    Formula NOTE 1 : Formula of spur and helical gears on surface durability (JGMA402-01)
    Kinematic viscosity of lubricant : 100cSt (50 deg C)
    Gear support : Support on one end
    Allowable Hertz stress σ Hlim (kgf/mm^2) : 106
    Safety factor SH : 1.15
  • Catalog No. : KRGCPF-H / KRGCPFD-H
    Formula NOTE 1 : Formula of spur and helical gears on surface durability (JGMA402-01)
    Kinematic viscosity of lubricant : 100cSt (50 deg C)
    Gear support : Support on one end
    Allowable Hertz stress σ Hlim (kgf/mm^2) : 112
    Safety factor SH : 1.15
  • Catalog No. : KRGCP / KRGCPF / KRGCPD / KRCPF
    Formula NOTE 1 : Formula of spur and helical gears on surface durability (JGMA402-01)
    Kinematic viscosity of lubricant : 100cSt (50 deg C)
    Gear support : Support on one end
    Allowable Hertz stress σ Hlim (kgf/mm^2) : 79
    Safety factor SH : 1.15
  • Catalog No. : SRGCP / SRGCPF / SRGCPFD
    Formula NOTE 1 : Formula of spur and helical gears on surface durability (JGMA402-01)
    Kinematic viscosity of lubricant : 100cSt (50 deg C)
    Gear support : Support on one end
    Allowable Hertz stress σ Hlim (kgf/mm^2) : 90
    Safety factor SH : 1.15
  • Catalog No. : SRCP / SRCPF / SRCPFD / SROCP / STRCPF / STRCPFD
    Formula NOTE 1 : Formula of spur and helical gears on surface durability (JGMA402-01)
    Kinematic viscosity of lubricant : 100cSt (50 deg C)
    Gear support : Support on one end
    Allowable Hertz stress σ Hlim (kgf/mm^2) : 52.5
    Safety factor SH : 1.15
  • Catalog No. : SURCPF / SURCPFD / FRCP
    Formula NOTE 1 : Formula of spur and helical gears on surface durability (JGMA402-01)
    Kinematic viscosity of lubricant : 100cSt (50 deg C)
    Gear support : Support on one end
    Allowable Hertz stress σ Hlim (kgf/mm^2) : 41.3
    Safety factor SH : 1.15
  • Catalog No. : MSCPG
    Formula NOTE 1 : Formula of spur and helical gears on surface durability (JGMA402-01)
    Kinematic viscosity of lubricant : 100cSt (50 deg C)
    Gear support : Support on one end
    Allowable Hertz stress σ Hlim (kgf/mm^2) : 166
    Safety factor SH : 1.15
  • Catalog No. : SSCPGS
    Formula NOTE 1 : Formula of spur and helical gears on surface durability (JGMA402-01)
    Kinematic viscosity of lubricant : 100cSt (50 deg C)
    Gear support : Support on one end
    Allowable Hertz stress σ Hlim (kgf/mm^2) : 99
    Safety factor SH : 1.15
  • Catalog No. : SSCPG
    Formula NOTE 1 : Formula of spur and helical gears on surface durability (JGMA402-01)
    Kinematic viscosity of lubricant : 100cSt (50 deg C)
    Gear support : Support on one end
    Allowable Hertz stress σ Hlim (kgf/mm^2) : 90
    Safety factor SH : 1.15
  • Catalog No. : KTSCP
    Formula NOTE 1 : Formula of spur and helical gears on surface durability (JGMA402-01)
    Kinematic viscosity of lubricant : 100cSt (50 deg C)
    Gear support : Support on one end
    Allowable Hertz stress σ Hlim (kgf/mm^2) : 74.5
    Safety factor SH : 1.15
  • Catalog No. : KSCP
    Formula NOTE 1 : Formula of spur and helical gears on surface durability (JGMA402-01)
    Kinematic viscosity of lubricant : 100cSt (50 deg C)
    Gear support : Support on one end
    Allowable Hertz stress σ Hlim (kgf/mm^2) : 112
    Safety factor SH : 1.15
  • Catalog No. : SSCP
    Formula NOTE 1 : Formula of spur and helical gears on surface durability (JGMA402-01)
    Kinematic viscosity of lubricant : 100cSt (50 deg C)
    Gear support : Support on one end
    Allowable Hertz stress σ Hlim (kgf/mm^2) : 49
    Safety factor SH : 1.15
  • Catalog No. : SUSCP
    Formula NOTE 1 : Formula of spur and helical gears on surface durability (JGMA402-01)
    Kinematic viscosity of lubricant : 100cSt (50 deg C)
    Gear support : Support on one end
    Allowable Hertz stress σ Hlim (kgf/mm^2) : 41.3
    Safety factor SH : 1.15

[NOTE 1] The gear strength formula is based on JGMA (Japanese Gear Manufactures Association) specifications. The units for the number of rotations (rpm) and the stress (kgf/mm^2) are adjusted to the units needed in the formula.
[NOTE 2] The allowable bending stress at the root σ Flim is calculated from JGMA401-01, and set to 2/3 of the value in the consideration of the use of planetary-, idler-, or other gear systems, loaded in both directions.

Definition of bending strength by JGMA 401-01 (1974)

The allowable bending strength of a gear is defined as the allowable tangential force at the pitch circle based on the mutually allowable root stress of two meshing gears under load.
The allowable bending strength
Example of the failure due to insufficient bending strength.

Definition of surface durability by JGMA 402-01 (1975)

The surface durability of a gear is defined as the allowable tangential force at the pitch circle, which permits the force to be transmitted safely without incurring
surface failure.
Definition of surface durability by JGMA 402 01
Example of the defacement due to insufficient surface durability.

3. Selecting Racks By Precision

The precision standards of KHK stock racks are established by us. Please be sure to see the pages below when selecting.

  1. Pitch Error of Racks NOTE 2 (KHKR001) – Page 190
  2. Precision of Rack Blanks NOTE 2 – Page 191
  3. Backlash of Rack Tooth – Page 191

[NOTE 2] Convert CP to m (module) when reference is made to the data in the table. (m=CP/π)

Application Hints

In order to use KHK stock gears safely, carefully read the Application Hints before proceeding. If there are questions or if you require clarifications, please contact our technical department or your nearest distributor.

KHK CO., LTD.
PHONE: 81-48-254-1744 FAX: 81-48-254-1765
E-mail info@khkgears.net

1. Caution on Performing Secondary Operations

  1. CP racks except for the racks where the gear teeth are induction hardened. To avoid problems of gear precision, do not reduce the face width. The precision of ground racks and racks with mounting holes may drop if you do not exercise extreme caution during installation or while modifying.
  2. Pitch lines of racks are controlled by using the bottom surface as the reference datum and over-pin measurements on tooth thickness. If you machine the bottom surfaces, the precision of the racks may be affected.
  3. When connecting two racks, the machining of the mating ends requires careful consideration. The meshing will be poor if the pitch (CP) straddling the connection has a positive tolerance. We recommend a minus tolerance on pitch of at the connection. The below is an indication of pitch tolerance for each module.
    Caution on Performing Secondary Operations 1
    Caution on Performing Secondary Operations 2
  4. To use dowel pins to secure racks, attach the racks to the base and drill both simultaneously.
  5. KHK stock CP racks made of S45C and SCM440 (except for ground racks) can be induction hardened. However, the precision of pitch is decreased.
  6. To be able to handle parts safely, all burrs and sharp corners should be removed after the secondary operations are done.
  7. If you are going to modify the gear by gripping the teeth, please exercise caution not to crush the teeth by applying too much pressure. Any scarring will cause noise during operation.

2. Points of Caution in Assembling

  1. KHK stock CP racks are designed to give the proper backlash when assembled using the mounting distance given by the formula below (mounting distance tolerance of H7 to H8 required). The backlash values are given in the table on Page 191. Make sure that the mounting distance stays constant for the length of the rack.
    Mounting distance a = Height of pitch line of rack + Pitch radius of pinion
    Points of Caution in Assembling 1
    [CAUTION] Pinions are assumed to be standard stock spur gears (x=0).
  2. KRGCP type of KHK stock ground racks have four surfaces ground parallel to within 10 – 15 μm. To maintain true angle, they should be mounted on high precision bases as shown below. It is even possible to correct for the angular errors of racks by compensating the mounting base. With recent increases in the requirement for zero backlash linear drives, such accurate assembly as shown is becoming more important.
    Points of Caution in Assembling 2
  3. If the racks are not secured properly to the base, they could shift during operation and cause unexpected problems. It is very important to insure firm mounting by the use of dowel pins or similar devices.
  4. Machined end type racks such as SRCPF and SRCPFD series have the pitch tolerance of – 0.1/- 0.3 for modules less than Module 2.5, and – 0.1/- 0.4 for larger modules. If you try to connect the racks without any space, the pitch at the connection will be too small and will cause problems. Please follow the following diagrams for assembly.

An example of Rack Joining, we recommend the following method.

An example of Rack Joining, we recommend the following method 1

An example of Rack Joining, we recommend the following method 2
[CAUTION] Joining gauge racks for helical racks must have the opposite hand from the racks. Please use Module 1-10 100 racks as a joining gauge rack, or alternatively the rack of the same specifications on hand.