Miter Gears: Technical Information
Characteristics∧ top
Miter gears are a special class of bevel gears where the shafts intersect at 90° and the gear ratio is 1:1. KHK stock miter gears are available in two types, spiral and straight tooth, with high precision grade for demanding torques and speeds, and commercial grade for economical applications. The following table lists the main features for easy selection.Secondary Operations: O = Possible, Δ = Partly Possible, X = Not Possible
Type | Catalog No. | Module | No. of Teeth ( ) Shaft Angle |
Material | Heat Treatment | Tooth Surface Finish | Precision JIS B 1704 : 1978 |
Secondary Operations | Features |
---|---|---|---|---|---|---|---|---|---|
Spiral Miter Gears | KMMSG | 2~4 | 20, 25, 30 | SCM415 | Carburized Note 1 | Ground | 1 | Δ | High strength, abrasion-resistant and compact for high speed & torque use. |
KSMSG | 2~5 | 20, 25, 30 | S45C | Gear teeth induction hardened | Ground | 2 | Δ | Reasonably priced ground gear, yet remachinable except for the gear teeth. | |
KMMSA• KMMSB | 1~10 | 20 | SCM415 | Carburized | Cut | 4 | X | Ready to use without performing secondary operations. Strong and abrasion resistant. | |
KMMS | 2~5 | 20, 25, 30 | SCM415 | Carburized Note 1 | Cut | 4 | Δ | Only teeth are induction hardened, allowing user to perform secondary operations elsewhere. | |
KSMS | 1~8 | 20, 25, 30 | S45C | Gear teeth induction hardened | Cut | 4 | Δ | Large numbers of teeth and modules are offered in these affordable spiral miter gears. | |
Zerol miter gears | KSMZG | 2~3 | 20 | S45C | Gear teeth induction hardened | Ground | 2 | Δ | A spiral miter gear with a helix angle less than 10°. Receives forces from the same direction as straight miter gears receive and have excellent precision properties.. |
Straight Miter Gears | KSMA• KSMB • KSMC | 1~8 | 20, 25, 30 | S45C | Gear teeth induction hardened | Cut | 4 | Δ | Usable without remachining, offered in 3 bore sizes. |
KMM | 2~5 | 20, 25, 30 | SCM415 | Carburized Note 1 | Cut | 4 | Δ | Compared to SM miters, these are stronger and less abrasive, and allow secondary operations. | |
KLM | 0.8~1.5 | 20 | SMF5040 (Equiv. to S45C) | — | Sintered | 5 | O | Mass-produced, low cost sintered products. Small and light weight. | |
KSM | 1~8 | 16, 20, 25, 30 | S45C | — | Cut | 3 | O | Popular straight miter for many uses. | |
KSAM | 1.5~3 | 20(45°, 60°, 120°) | S45C | — | Cut | 3 | O | 3 types are available for shafts at 45°, 60° and 120°. | |
KSUM | 1~4 | 20, 25 | SUS303 | — | Cut | 3 | O | Suitable for food machinery due to SUS303’s rust-resistant quality. | |
KSUMA | 1~4 | 20, 25 | SUS303 | — | Cut | 3 | Δ | Stainless steel products, usable without remachining. | |
KPM | 1~4 | 20, 25 | MC901 | — | Cut | 4 | O | MC nylon products are light and can be used without lubricant. | |
KDM | 0.5~1.5 | 20 | DURACON (M90-44) | — | Injection Molded | 6 | Δ | Injection molded, mass-produced products, suitable for office machines. |
We use Crowning method for gear cutting
KHK utilizes Gleason Coniflex No.104, 102 and 114 bevel gear generating machinery, also equipped for mass production of straight miter gears. You can count on a stable supply of economically priced straight miter gears from KHK
KHK utilizes Gleason Coniflex No.104, 102 and 114 bevel gear generating machinery, also equipped for mass production of straight miter gears. You can count on a stable supply of economically priced straight miter gears from KHK



Selection Hints∧ top

1. Caution in Selecting Mating Gears
Among KHK stock miter gears, there are products which are not interchangeable even when the module and the number of teeth are the same. Also, spiral miter gears require additional consideration since the right-hand mates with the left-hand spiral as shown in the table below.
Straight Miter O = Allowable, X = Not Allowable
Catalog No. | KSMA KSMB KSMC |
KMM | KSM | KSUM | KSUMA | KPM | KDM | KLM | KSAM |
---|---|---|---|---|---|---|---|---|---|
KSMA • KSMB • KSMC | O | O | O | O | O | O | X | X | X |
KMM | O | O | O | O | O | O | X | X | X |
KSM | O | O | O | O | O | O | X | X | X |
KSUM | O | O | O | O | O | O | X | X | X |
KSUMA | O | O | O | O | O | O | X | X | X |
KPM | O | O | O | O | O | O | X | X | X |
KDM | X | X | X | X | X | X | O | X | X |
KLM | X | X | X | X | X | X | X | O | X |
KSAM | X | X | X | X | X | X | X | X | O |
Spiral Miter O = Allowable, Δ = Allowable in certain cases, X = Not Allowable
Catalog No. | Series | MMSG | SMSG | MMSA MMSB | MMS | SMS |
---|---|---|---|---|---|---|
Series | Spiral hand | R | R | R | R | R |
MMSG | L | O | X | X | X | X |
SMSG | L | X | O | X | X | X |
MMSA • MMSB | L | X | X | O | Δ | X |
MMS | L | X | X | Δ | O | X |
SMS | L | X | X | X | Δ | O |
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 their own values by applying the actual usage conditions. To learn more about the strength calculations, please refer to the technical information contained in the "Bending Strength of Bevel Gears" section and the "Surface Durability of Bevel Gears" section.
Catalog No. Item | KMMSG KMMSA • KMMSB KMMS • KMM | KSMSG • SMZG KSMS KSMA• KSMB• KSMC | KSM KSAM | KSUM KSUMA KLM NOTE 3 | KPM | KDM |
---|---|---|---|---|---|---|
Calculation assumptions for Bending Strength of Gears | ||||||
Formula NOTE 1 | Formula of bevel gears on bending strength (JGMA403-01) | The Lewis formula | ||||
No. of teeth of mating gear | Same number of teeth | — | ||||
Rotation | 100rpm(600rpm for KMMSG, KSMSG and KSMZG) | 100rpm | ||||
Durability | Over 107cycles | — | ||||
Impact from motor | Uniform load | Allowable bending stress(kgf/mm²) | ||||
Impact from load | Uniform load | 1.15 (40°C with No Lubrication) | m 0.5 4.0 m 0.8 4.0 m 1.0 3.5 m 1.5 1.8 NOTE 3 (40°C with Grease Lubrication) |
|||
Direction of load | Bidirectional | |||||
Allowable bending stress at root σFlim(kgf/mm²) NOTE 2 | 47 | 21 | 19 | 10.5 | ||
Safety factor KR | 1.2 | |||||
Calculation assumptions for Surface Durability (Except those in common with bending strength) | ||||||
Formula NOTE 1 | Formula of bevel gears on bending strength(JGMA404-01) | — | — | |||
Kinematic viscosity of lubricant | 100cSt (50°C) | |||||
Gear support | Shafts & gear box have normal stiffness, and gears are supported on one end | |||||
Allowable Hertz stress σHlim (kgf/mm²) | 166 | 90 | 49 | 41.3 | ||
Safety factor CR | 1.15 |
Application Hints∧ top
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.1. Caution on Performing Secondary Operations
- If you are reboring, it is important to pay special attention to locating the center in order to avoid runout.
- The reference datum for gear cutting is the bore. Therefore, it is best to use the bore for locating the center. If it is too difficult to do for small bores, the alternative is to use one spot on the bore and the runout of the side surface.
- If reworking using scroll chucks, we recommend the use of new or rebored jaws for improved precision. Please exercise caution not to crush the teeth by applying too much pressure. Any scarring will cause noise during operation.
- For items with induction hardened teeth, such as SMSG and SMS series, the hardness is high near the tooth root. When machining the front face, the machined area should be 4 to 6mm smaller than the dimension, J.
- For tapping and keyway operations, see the examples given in "1. Caution on Performing Secondary Operations" in KHK Stock Spur Gear section. When cutting keyways, to avoid stress concentration, always leave radii on corners.
- PM plastic miter gears are susceptible to changes due to temperature and humidity. Dimensions may change between during and after remachining operations.
- When heat-treating S45C products, it is possible to get thermal stress cracks. It is best to subject them to penetrant inspection afterwards. If tooth strength is not sufficient, it can be increased approximately four times by heat-treating. On the other hand, the precision of the gear will drop about one grade.
2. Points of Caution in Assembling
- Since miter gears are cone shaped, they produce axial thrust forces. Specifically with regard to spiral miter gears, the directions of thrust change with the hand of spiral and the direction of rotation.
This is illustrated below. The bearings must be selected properly to be able to handle these thrust forces. For more technical information see the section "Gear Forces".
- If a miter gear is mounted on a shaft far from the bearings, the shaft may bend. We recommend mounting bevel gears as close to the bearings as possible. This is especially important since most miter gears are supported on one end. The bending of shafts will cause abnormal noise and wear, and may even cause fatigue failure of the shafts. Both shafts and bearings must be designed with sufficient strength.
- Due to the thrust load of miter gears, the gears, shafts and bearings have the tendency to loosen up during operation. Miter gears should be fastened to the shaft with keys and set screws, taper pins, step shafts, etc.
- When installing KMMSA or KMMSB finished bore spiral miter gears in B7 style (ring type), always secure the gears onto the mounting base with taper pins to absorb the rotational loads. It is dangerous to secure with bolts only.
- KHK stock miter gears are designed such that, when assembled according to the specified mounting distance with a tolerance of H7 to H8, the backlash shown in the table are obtained. Mounting distance error, offset error and shaft angle error must be minimized to avoid excessive noise and wear. Inaccurate assembly will lead to irregular noises and uneven wear. Various conditions of teeth contact are shown below.
Correct Tooth Contact
When assembled correctly, the contact will occur on both gears in the middle of the flank and center of face width but somewhat closer to the toe.
When assembled correctly, the contact will occur on both gears in the middle of the flank and center of face width but somewhat closer to the toe.

Incorrect Tooth Contact
Mounting Distance Error
When the mounting distance of the pinion is incorrect, the contact will occur too high on the flank on one gear and too low on the other.
When the mounting distance of the pinion is incorrect, the contact will occur too high on the flank on one gear and too low on the other.

Offset Error
When the pinion shaft is offset, the contact surface is near the toe of one gear and near the heel of the other.
When the pinion shaft is offset, the contact surface is near the toe of one gear and near the heel of the other.

Shaft Angle Error
When there is an angular error of shafts, the gears will contact at the toes or heels depending on whether the angle is greater or less than 90°.
When there is an angular error of shafts, the gears will contact at the toes or heels depending on whether the angle is greater or less than 90°.

3. Application Examples

