Bevel Gears: Technical Information
Characteristics∧ topKHK 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
|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.|
- 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|
Selection Hints∧ topPlease 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|
|Gear / Pinion||KMBSG||KSBSG||KMBSA, KMBSB||KSBS|
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.
|Catalog No. Item||KMBSG, KMBSA, KMBSB||KSBSG, KSBZG, KSBS||KSB, KSBYNOTE 3||KSUB||KPB||KDB|
|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|
|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|
Application Hints∧ topIn 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 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.
- 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.
- KPB plastic bevel 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. While the teeth strength may increase for fold, the precision of the gear will drop approximately one grade
- For the handling conveniences, the KSB and KSBY series listed below has the tapped holes (180o apart, 2 places) on the holding surface.
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
- 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".
- 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.
- 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.
- 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.
- 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".
3. Application Examples
High-Ratio Hypoid Gears∧ topFeatures 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.
- Total-cost reduction
The KMHP provides a compact gearing body replacing several stages of reduction gears. This reduces the cost sharply.
- 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).
- High rigidity
The carburized hypoid gears lead to smaller size than comparable worms gears.
- Compact gear assembly
The size of the gear housing is nearly the same as outer diameter of the large gear. (See the diagrams below)
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.