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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.
NOTE 1: Although these are carburized products, secondary operations can be performed as the bore and the hub portions are masked during the carburization. However, as a precaution, high hardness (HRC40 at maximum) occurs in some cases.
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

Cutting Gears Cutting Gears Graph Gleason Coniflex No 104

Selection Hints∧ top

Miter Gear Thread Direction 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.

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
CAUTION: For selecting items in the "Δ" category, please reconfirm with us that the pair can work.
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
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 number of rotations (rpm) and the the stress (kgf/mm²) are adjusted to the units needed in the formula. NOTE 2: The allowable bending stress at the root ØFlim is calculated from JGMA403-01, 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: The values of the allowable bending stresses for DM m1.5 and the allowable root bending stress for LM gears are our own estimates.

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
  1. If you are reboring, it is important to pay special attention to locating the center in order to avoid runout.
  2. 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.
  3. 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.
    Lathe Operations
  4. 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. Machining Smaller Face
  5. 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.
  6. PM plastic miter gears are susceptible to changes due to temperature and humidity. Dimensions may change between during and after remachining operations.
  7. 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
  1. 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". Drive Diagram 2 Drive Diagram
  2. 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. Example of Assembling
  3. 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.
  4. 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.
    Mounting Base
  5. 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.
Tooth Contact

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.
Mounting Distance Error
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.
Offset Error
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°.
Shaft Angle Error



3. Application Examples
Example 1
Example 1
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