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Bevel Gears: Technical Information

Characteristics∧ top

KHK stock bevel gears are available in two types, spiral and straight tooth, in gear ratios of 1.5 through 5, and are offered in a large variety of modules, numbers of teeth, materials and styles. The following table lists the main features for easy selection.

Secondary Operations: O = Possible, Δ = Partly Possible, X = Not Possible
Type Catalog No. Module Gear Ratio Material Heat Treatment Tooth Surface Finish Precision
JIS B 1704 : 1978
Secondary Operations Features
Hypoid Gear MHP 1~1.5 15~200 SCM415 Carburized Note 1 Cut 3 Δ High speed reduction ratio, high efficiency, high rigidity and compact gear assembly.
Spiral Bevel Gears KMBSG 2~4 2 SCM415 Carburized Note 1 Ground 1 Δ High strength, abrasion-resistant and compact for high-speed & torque use.
KSBSG 2~4 1.5~3 S45C Gear teeth induction hardened Ground 2 Δ Reasonably priced ground gear,
yet remachinable except for the gear teeth.
KMBSA • KMBSB 2~6 1.5~3 SCM415 Carburized Cut 4 X Ready to use without performing secondary operations. Strong and abrasion resistant.
KSBS 1~5 1.5~4 S45C Gear teeth induction hardened Cut 4 Δ Large nos. of teeth and modules are offered in these affordable spiral bevel gears.
Zerol Bevel Gears KSBZB 2~3 1.5~2 S45C Gear teeth induction hardened Ground 2 Δ A spiral bevel gears with a helix angle less than 10°. Receives forces from the same direction as straight bevel gears receive and have excellent precision properties.
Straight Bevel Gears KSB • KSBY 1~8 1.5~5 S45C Cut 3 O Popular series of straight bevel gears for many uses.
KSUB 1.5~3 1.5~3 SUS303 Cut 3 O Suitable for food machinery due to SUS303's rust-resistant quality.
KPB 1~3 1.5~3 MC901 Cut 4 O MC nylon products are light and can be used without lubricant.
KDB 0.5~1 2 Duracon (M90-44) Injection Molded 6 Δ Injection molded, mass-produced productions, 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.
  • For safe handling and to prevent damage such as deformation, KHK stock bevel gears have round chamfering at the corners, on the top surface plane of a gear tooth.

• The chamfering of the corner gear tips for bevel gears
Module Outside edge R Inside edge R
0.5 up to 1 0.5 All burrs removed
1 up to 2.5 1 0.5
2.5 up to 5 2 1
Over 5 3 1.5

Integrated combination of cutting-edge technologies and know-how.
The popularity in our large selection of product lineups is established by a production system integrated with advanced manufacturing technology and know-how, achieving quality products.

Straight Cutting Bevel Gears
Spiral Bevel Gears
Gleson Machine
Injection Molded

Selection Hints∧ top

Mating Gears 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
Basically, KHK stock bevel gears should be selected as shown in the catalog in pairs (e.g. KMBSG2-4020R should mate with KMBSG2-2040L). But, for straight tooth bevel gears, there is some interchangeability with different series. For plastic bevel gears, we recommend metal mating gears for good heat conductivity.

Selection Chart for Bevel Gears (O = Allowable, X = Not Allowable)
Straight Bevel Gears
Gear / Pinion KSB KSUB KPB KDB
Spiral Bevel Gears

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 strength calculation, please refer to the technical information contained in the "Bending Strength of Bevel Gears", and the "Surface Durability of Bevel Gears" section.

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 No. of teeth of the mating gear of the set
Rotation 100rpm (600rpm for KMBSG, KSBSG, KSBZG) 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
(40°C with Grease Lubrication)
Direction of load Bidirectional
Allowable bending stress at root σFlim(kgf/mm²) NOTE 2 47 21 19 (24.5) 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 (62.5) 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. Also, the units (rpm) of number of rotations and unit (kgf/mm2) of stress are adjusted to the units needed in the formula. NOTE 2: The allowable bending stress at the root σFlim 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: Since SB Bevel Pinion Shafts are thermally refined, the allowable tooth-root bending stress and allowable hertz stress are referred to the value shown in parentheses.

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 KSBSG and KSBS 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. KPB plastic bevel 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. While the teeth strength may increase for fold, the precision of the gear will drop approximately one grade
  8. For the handling conveniences, the KSB and KSBY series listed below has the tapped holes (180o apart, 2 places) on the holding surface.
    Bevel Diagram
    Catalog No. L (mm) Tap Size
    KSB6-4515 130 M10 deep 15
    KSBY8-4020 160 M10 deep 15
    KSBY8-4515 210 M10 deep 15
    KSBY5-6015 160 M10 deep 15
    KSBY6-6015 220 M10 deep 15

2. Points of Caution in Assembling
  1. Since bevel gears are cone shaped, they produce axial thrust forces. Especially for spiral bevel 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 bevel 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.
    NOTE: Bevel gears with the gear ratio 1.57 or less, produce a thrust force which has the same direction as miter gears. For details, see page 422.
  3. Due to the thrust load of bevel gears, the gears, shafts and bearings have the tendency to loosen up during operation. Bevel gears should be fastened to the shaft with keys and set screws, taper pins, step shafts, etc.
  4. When installing KMBSA or KMBSB spiral bevel 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 bevel gears are designed such that, when assembled according to the specified mounting distance with a tolerance of H7 - H8, the backlash shown in the table is obtained. Mounting distance error, offset error and shaft angle error must be minimized to avoid excessive noise and wear. For various conditions of teeth contact, please see the following illustrations, "Correct Tooth Contact" and "Incorrect Tooth Contact".
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 2 Example 3

High-Ratio Hypoid Gears∧ top

Features of KMHP High Ratio Hypoid Gears
A pair of KMHP high-ratio hypoid gears are able to produce an amazing reduction of speed of 200:1 in one stage.
Comparison of Hypoid Gears
  1. Total-cost reduction
    The KMHP provides a compact gearing body replacing several stages of reduction gears. This reduces the cost sharply.
  2. High efficiency
    Compared to worm gear drives, the KMHP has less sliding contact. The resulting higher efficiency allows the use of smaller motors (See the graph on the right).
  3. High rigidity
    The carburized hypoid gears lead to smaller size than comparable worms gears.
  4. Compact gear assembly
    The size of the gear housing is nearly the same as outer diameter of the large gear. (See the diagrams below)

Comparison ofKMHP Gears Radial Load Calculations
Variations in tooth contact due to poor alignment of gears
If the gear engagement position is out of the normal position, variations in tooth contact, as illustrated below, may appear.

Alignment Variation 1 Alignment Variation 2 Alignment Variation 3 Alignment Variation 4