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Gear Racks Gear Racks - Technical Data

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Racks

KHK stock racks are made for high precision linear motion applications. We offer a large selection of racks ranging from module 0.5 to 10 and lengths from 100 to 2000 mm. The following table lists the main features.

Features of Racks gears - data table

Pinions

Features of Pinion Gears - data table
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) and (K) have mounting screw holes for easier assembly.
Note 2 Products with module less than 0.8 are thermal refined, without their gear teeth being induction hardened.
Note 3 Precision grade standard of racks are set by KHK. Please see "Precision of Racks" in Selection Hints section for details.


• For safe handling and to prevent damage such as deformation, KHK stock racks have round chamfering at the corners of the top land of the gear tooth.

This rounded chamfered shape is patented by KHK. It is also effective for reducing noise.

• Black 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.



Application Examples

KHK stock racks & pinions are adopted in driving devices for all kinds of linear motion systems, including transport devices.

Automatic packaging machine manufactured by Toyota Machinery Co., ltd.

Automatic packaging machine manufactured by the Toyota Machinery Co. - Image Example
KSUR stainless steel rack used for film winding tension part

Dremax long strip cutter

Dremax long strip cutter - Image Example
KPR plastic rack used for feeding Long Strip Cutter


Lathe auto loader

Lathe auto loader - Image Example
KSRO Round Rack used as a workpiece storage device (lifting/lowering table)


Lathe gantry loader

Lathe gantry loader - Image Example
KKRG Ground Rack used as a workpiece conveying device


Packaging Machine

Packaging machine - Image Example
KSR Rack used for label feeding


Extruder (design example)

Extruder design - Image Example
KSRO Round Rack used for extruders (can also become a lifting/lowering device by setting up vertically)


Film Sealer

Film sealer - Image Example
KSRO Round Rack used for extruders (can also become a lifting/lowering device by setting up vertically)


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 "CAUTION" notes shown below before the final selection.

Caution when selecting the mating gears

1. With the exception of helical racks, KHK stock racks can mate with any spur gears of the same module. Products with different tooth width can also be mated as a pinion.

2. There are limited choices of mating gears for KKRHG/KKRHGF, KSRHEF, and KSRH Ground Helical Racks and Helical Racks. Be sure to check the helix direction (right or left) when selecting.

Caution when selecting gears based on gear strength

Allowable bending strength and surface durability values shown in product tables were computed by assuming a certain application environment. They should be used as reference only. We recommend that each user computes their own values by applying the actual usage conditions. The table below contains the assumptions established for various products in order to compute gear strengths.

Calculation of bending strength of gears

Calculation of bending strength og gears - table

Calculation of surface durability

Except where it is common with bending strength
Calculation of surface durability, except where it is common with bending strength - table
Note 1 The gear strength formula is based on JGMA (Japanese Gear Manufacturers Association) specifications, "MC Nylon Technical Data" by Nippon Polypenco Limited and "Duracon Gear Data" by Polyplastic Co. The units for the rotational speed (rpm) and the stress (kgf/mm2) are adjusted to the units needed in the formula.
Note 2 The allowable bending stress at the rooσtF lim 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.
NOTE 3 For KSRG, or KSRGF Ground Racks, with a module less than m 0.8, the allowable bending stress and allowable hertz stress are respectively 24.5 (kgf/mm2) and 62.5 (kgf/mm2). NOTE 4 The values for DR m 1.5 racks were assumed by KHK. Usage conditions for KSSDR (DR Rack Pinion) are the same as for the SSCP Pinion.

Mating Helical Gear Selection Chart

O = Allowable • X = Not allowable
Mating Helical Gear Selection Chart - table
Direction of helix in mating helical gear racks - image


Alert! Important InformationWhen selecting KHK standard gears, glance over the Cautions on Product Characteristics and Cautions on Performing Secondary Operations in the respective dimension tables.


1. Products not listed in this catalog or materials, modules, number of teeth and the like not listed in the dimensional tables can be manufactured as custom items.

2. The color and shape of the product images listed on the dimension table page of each product may differ from the actual product. Be sure to confirm the shape in the dimension table before selection.

3. The details (specifications, dimensions, prices, etc.) listed in the catalog may be changed without prior notice.


Alert! Important InformationThe most important factor in selecting gears is the gear strength.

Determine the actual load torque applied to the gear and the gear type suitable for the purpose.

Definition of bending strength of gears

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.

Example of failure due to insufficient
bending strength

Definition of bending strength of gears - image

Definition of surface durability of gears

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. The allowable gear tooth load of a gear is defined as the allowable tangential force at the pitch circle based on the mutual gear tooth strength of two meshing gears under load.

Example of wear due to insufficient
surface durability

Definition of surface durability of gears - image
Select provisionally from the allowable torque table of the Master Catalog based on the load torque.
Provisional selection from the master catalog - image



Alert! - Important InformationWe recommend that each user computes their own values by applying the actual usage conditions to determine the suitability of the gear strength.

Calculate the strength formally using the various gear strength formulas (Get them here).

Cautions on selecting racks by precision

The precision standards of KHK stock racks are established by us. The table below indicates the tolerance ranges of our racks.

1. Pitch Errors of Racks (KHK R 001)
Our precision grades for pitch errors are established by referring to JIS Standards. The precision grades are set from 1 to 8, in accordance with the tolerance of a single pitch error (S.P.E.), adjacent tooth-to-tooth error (T.T.E.), and the total composite error (T.C.E.) for each module and length.

Precision grades of racks (KHK R 001) - Unit: µm

Precision grades of racks (KHK R 001) - Unit: µm - table
Note 1. Since the pitch accuracy of racks may vary due to humidity, the precision grades are evaluated at the bottom surface of the product, at the temperature of 20℃ . The dimensions of the KHK KPR Plastic Racks may vary widely due to humidity. Therefore, the total composite error is assumed to be excluded from this accuracy standard.
Please refer in our separate technical reference book to "Design of Plastic Gears" (Page 100) for change in dimensions.
Note 2 For the accuracy of KCP Rack, convert KCP to m (module) when reference is made to the data in the tabmle. =( KCP/ π ).

Pitch inspection and a sample report using Karl Zeiss UMC-550 Coordinate Measuring Machine. (KHK R 001 Grade 1)

Pitch inspection and a sample report using Karl Zeiss UMC-550 Coordinate Measuring Machine. (KHK R 001 Grade 1) - Image

2. Precision of rack blanks

Tolerance on facewidth and height

Tolerance on facewidth and height - Image
Tolerance on face width and height - Table
Note 1. Dimensional tolerance of hardened products is that prior to hardening. Dimensional tolerance for plastic racks is the value obtained when machining is performed, and may increase slightly due to aging. * KBSR products are not applicable.

Maximum curvature values (flatness tolerance L)

Maximum curvature values - Image
Straightness tolerances of round racks - Table
Note: The straightness tolerances of round racks are 0.15/500 mm and 0.2/1000 mm. Plastic racks change over time so are excluded from this precision standard.


Tolerance on total length - Unit: mm

Tolerance on total length - Table
Note: For Type-F racks with machined ends, the dimensional tolerance is a calculated value according to assumed usage conditions, without consideration of pitch errors and aged deterioration.


Backlash of rack teeth (Amount of tooth thinning) - Unit: mm

Backlash of rack teeth - Table
Note The values shown in the table are amount of tooth thinning. The theoretical backlash of assembled rack and pinion is given by:
Rack and pinion backlash = Amount of tooth thinning of the rack + amount of tooth thinning of the pinion
Amount of tooth thinning of the rack : See above table
Amount of tooth thinning of the pinion : Take 1/2 of backlash given in the product table


Application Hints
In order to use KHK stock gears safely, carefully read the Application Hints before proceeding. If there are questions or you require clarifications, please contact our technical department or your nearest distributor. TEL: (646) 396-GEAR FAX: (516) 437-6700 E-mail: qtcsupport@qtcgears.com

Caution on Handling

1. KHK products are packaged one by one to prevent scratches and dents, but if you find issues such as rust, scratches, or dents when the product is removed from the box after purchase, please contact the supplier.

2. Depending on the handling method, the product may become deformed or damaged. Resin gears and ring gears deform particularly easily, so please handle with care.

Caution on Performing Secondary Operations

1.Secondary operations can be performed on all KHK stock racks except for the racks with their gear teeth 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 in terms of the pitch (p) accuracy. The meshing will be poor if the pitch 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.

Pitch tolerance for rack modules

4. To use dowel pins to secure racks, attach the racks to the base and drill both simultaneously.

5. KHK stock 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.


Points of caution during assembly

KHK stock racks are designed to give the proper normal direction 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 193. 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
Mounting distance a =  height of pitch line of rack + pitch radius of pinion - illustration

2. KKRG type of KHK stock ground racks have four surfaces ground parallel with high precision. To maintain true angle, they should be mounted on high precision bases (within 10μm recommended) 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.
Illustration of racks not properly secured

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 KSRF and KSRFD series have the pitch tolerance of -0.05 to -0.4mm at the end face. 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.

5. With KSRFD etc., if using more than 10 racks connected together to form a rack with mounting holes machined along a length of 1 meter, the pitch precision and machining precision may cause the rack and base mount-ing holes to deviate, leading to set screw interference with the counterbored hole and preventing mounting. When using a rack for long lengths such as 10 meters or 20 meters, have the mounting holes additionally machined into long holes.

As an example of rack joining, we recommend the following method.


Example of recommended rack joining - Illustration

How to mount racks on a mounting base (for KSRFD2-1000)


How to mount racks on a mounting base (for KSRFD2-1000) - Illustration

Cautions on Starting

1. Check the following items before starting.
  • Are the gears installed securely?
  • Is there uneven tooth contact?
  • Is there adequate backlash? Be sure to avoid zero-backlash.
  • Has proper lubrication been supplied?
2. If gears are exposed, be sure to attach a safety cover to ensure safety. Also, be careful not to touch rotating gears.

3. Gears can be lubricated with the "grease lubrication method", "splash lubrication method (oil bath method)", or "forced lubrication method (circulation lubrication method)". For initial operation, the lubricant may deteriorate markedly, so check the condition of the lubricant after starting.


Alert! - Important InformationFor more technical information, please see the section "Gear Lubrication" of our technical reference book.
4. If there is any abnormality such as noise or vibration during startup, check the gears and assembly condition. "High gear accuracy", "smooth gear teeth surface" and "correct tooth contact" are some of the measures against gear noise.


Alert! - Important InformationFor more technical information, please see the section "Gear Noise" (Here).
KHK considers safety a priority in the use of our products. When handling, adding secondary operations, assembling, and operating KHK products, please be aware of the following issues in order to prevent accidents.

Warning: Precautions for preventing physical and property damagePrecautions for preventing physical and property damage


1. When using KHK products, follow relevant safety regulations (Occupational Safety and Health Regulations, etc.).

2. Pay attention to the following items when installing, removing, or performing maintenance and inspection of the product.
  • Turn off the power switch.
  • Do not reach or crawl under the product.
  • Wear appropriate clothing and protective equipment for the work.

Caution in preventing accidentsCautions in preventing accidents


1. Before using a KHK product, read the precautions in the catalog carefully in order to use it correctly.

2. Avoid use in environments that may adversely affect the product.

3. Our products are manufactured under a superior quality control system based on the ISO9000 quality management system; if you notice any malfunctions upon purchasing a product, please contact the supplier.


Comparision of Racks & Pinions and Ball Screws
Since racks are a simple mechanism, the material, hardening, strength and precision can be designed according to the environment.

They are also inexpensive, with parts that can be purchased separately for replacement. In the designing process, please refer to Features of Racks & Pinions and Ball Screws in the table below.
Comparision of racks, pinions and ball screws

Features of racks & pinions

Features of racks and pinions

Features of ball screws

Features of ball screws
Laser Hardened Racks
Comparision of Racks & Pinions and Ball Screws
Since racks are a simple mechanism, the material, hardening, strength and precision can be designed according to the environment.

They are also inexpensive, with parts that can be purchased separately for replacement. In the designing process, please refer to Features of Racks & Pinions and Ball Screws in the table below.
Comparision of racks, pinions and ball screws


Rack downsizing
The H Series, KHK stock racks with induction hardened gear teeth, and the KHL Series, with laser hardening, are available.

The graph below simulates the downsizing of KHK stock racks. It is possible to reduce the module (size) with equivalent transmission power, or to reduce the price likewise. Please select a product that fits your needs.

Comparison table of permissible transmission force of hardened racks

Comparison table of permissible transmission force of hardened racks

Comparison table per series (module 3, rack length: 1,000 mm)

Comparison table of permissible transmission force of hardened racks

Example of rack downsizing

The surface durability can be increased by hardening the gear teeth. By increasing the strength thus, the angular dimensions of modules and racks can be re-duced. This helps reduce the cost.

Example of rack downsizing - example