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CP Racks and Pinions CP Racks & Pinions- Technical Data

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CP Racks & Pinions

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. (KFRCP is available to 4000 mm)

Features of CP Racks - data table

Pinions

Features of Pinion Gears For CP Racks - 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. They can be butt-jointed 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. It is also effective for reducing noise.

• Black products are KHK stock CP racks & pinions that have an applied black oxide coating for rust resistance. This "blackness" is a product characteristic of KHK stock gears.



CP racks & pinions are ideal for linear positioning.


CP Racks and Pinions

CP Racks & Pinions

The reference pitch of a metric module is computed by multiplying the module number m by π (3.14159). For example, the reference pitch of m3 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. Circular pitch products solve these problems. This problem is solved by CP racks and pinions where one rotation of a pinion moves it precisely 50, 100, 150, ... 600 mm, etc. The following table lists the main features.

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


CP Racks and Pinions

KSTRCPF / KSTRCPFD / KKTSCP
Taper Racks & Pinions


Easy to adjust the backlash
Normally, the backlash is adjusted by the mounting distance (height of pinion shaft), but for KHK Tapered Racks & Pinions, it can simply be adjusted by moving the pinion mounting position in the axial direction.

Backlash within 0.05 mm
The backlash of the conventional stock racks & pinions (KSRCP5-1000 & KSSCP 5-30) is 0.09 to 0.25 mm, but KHK Tapered Racks & Pinions (KSTRCPF5-1000 & KKTSCP5-30) are manufactured within 0.05 mm.

Thrust load is not applied
KHK Tapered Racks & Pinions are basically straight racks & spur gears.
Although the pinion looks like a bevel gear, it is actually a profile shifted gear whose tooth thickness in the helix direction is continuously changed.

Therefore, as with ordinary racks & pinions, you can use them without worrying about the thrust load.

Assembly and backlash adjustment method

• Assemble at the mounting distance of the theoretical value at the reference tooth position of the racks & pinions.For the mounting distance and backlash, see the dimension table of the tapered spur gear.

• The backlash can be adjusted by moving the tapered spur gear in the axial direction. Moving it by 1 mm will adjust the backlash by 0.05 mm.

• When the tapered spur gear is pushed to the large end of the rack, the backlash is reduced. Conversely, retracting it will increase the backlash.

Assembly and backlash adjustment method


Application Examples

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

Rack rail assembly

Rack Rail Assembly - Image Example

Rack drive linear guide

Rack Drive Linear Guide - Image Example

Rack guide for robot travel

Rack guide for robot travel - Image Example



Examples of using tapered spur gears

Changing the assembly direction of the tapered spur gear or assembling it with a general spur gear will allow it to be used at the axial angle shown below.

When the boss is set in the opposite direction, the axial angle is 0° (parallel shaft).
When the boss is set in the opposite direction, the axial angle is 0° (parallelshaft).
When the boss is set in the same direction, the axial angle is 8°.
When the boss is set in the same direction, the axial angle is 8°.
When the taper spur gear and general spur gear are set, the axial angle is 4°.
When the taper spur gear and general spur gear are set, the axial angle is 4°.



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. 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, selecting the proper mating gear should be verified to make sure that the items are correct. Otherwise, complications could arise.

2. KSTRCPF and KSTRCPFD Tapered Racks are mated with KKTSCP Spur Gears having the same pitch. They can also be mated with other spur gears; however, they cannot be used as parallel axis gears due to the setting angles.

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 of 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, 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.

Calculation 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

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 CP racks except for the racks where the gear teeth are induction hardened. 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 end pitch (CP) requires careful consideration. 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.

The below is an indication of pitch tolerance for each module.

Pitch tolerance for CP rack modules

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.


Points of caution during assembly

KHK stock CP 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).

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


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. KKRGCP type of KHK stock ground racks have four surfaces ground parallel to within 10 ~ 15μm. In order to maintain the straightness, set it on a mounting base with high accuracy as shown below to correct the straightness error of the rack gear. Recently, no-backlash drive is often required, so assemble as shown below.
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 KSRCPF and KSRCPFD series have 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 KSRCPFD 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 mounting 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.