2026 September 2nd Week FK News Recommendation - Transmission Orientations

Hypoid gearsets are used as final drive gears in cars and trucks. Hypoid gears are not used as simple reducers, but their purpose is to redirect rotation and torque by a certain angle, commonly 90°. In case of hypoids, the second purpose of lowering the center of gravity of a vehicle body has become very important in the automotive and truck industry. The redirection of rotation and torque has to be done at the driving axle of a vehicle. The engine orientation of vehicles with a rear wheel drive is longitudinal. Because engines of cars and trucks are commonly in the front, a longitudinally oriented propeller shaft transmits the engine rotation to the rear drive axle, as shown in Figure 17. The transmission, which is located between the engine and the propeller shaft, needs to have a gear shaft orientation identical to the direction of the engine crankshaft. The hypoid gearset redirects rotation and torque and provides the final reduction at the drive axle. The advantage of this concept is the lower torque in the complex shift or automatic transmission, and the high torque only at the ring gear at the drive axle.

Is Lapping an Attempt to Make Hypoid Gears Conjugate? Lapping, like grinding, is a hard finishing process. In grinding the same profile and length crowning applied in the soft cutting process is created. Grinding re-establishes the original surface function after the heat treatment. In lapping material is only removed in the tooth contact area. This not only establishes a good rolling condition, but it also makes the flank surfaces more conjugate in the area where the tooth contact patterns are located. Lapping and grinding are hard-finishing operations. The soft-manufactured bevel and hypoid gearsets must be heat-treated, which in the most common case begins with a case carburizing of standard gear steels such as AISI 8620 or 16MnCr5. To give the low-carbon steel a surface hardness in the 60 HRc range, a layer of carbon enrichment below the surface of 0.8 to 1.5 mm depth is placed by a diffusion process. After the carburizing and quenching in oil, an additional tempering takes place. The result is a surface hardness that is commonly close to 60HRc and a core hardness in the 30HRC range. Case hardening provides an ideal transition between surface and core hardness that makes gears on the surface hard and wear resistant, and in the core ductile. This makes shock loads and certain small plastic deformations tolerable without failure of the gearset. One major side effect of the heat treatment process is the distortion of the gears that is caused by carburizing, the recrystallization of the steel, and the quenching. To make a gearset after heat treatment suitable for power transmissions, for example, in cars and trucks, a hard-finishing operation is required. The hard-finishing operating eliminates the heat treatment distortions hereby providing the flank surfaces with the correct geometry from before the heat treatment. In addition, hard finishing improves the surface finish to a low roughness and waviness, which enhances the hydrodynamic lubrication and reduces noise. Grinding and skiving are the preferred hard-finishing methods, creating a defined surface form that duplicates the original designed surfaces in the single micron range. In case of face hobbed bevel and hypoid gearsets, grinding is not possible, because of the epicyclical flank lead function. Skiving can generate epicyclical lead functions but is not yet accepted for the high production volumes in the automotive and truck industry. This leaves only the lapping process for the hard-finishing of face-hobbed angular gearsets. However, the face hobbed surface texture and the relative sliding between the flanks of hypoid gears make lapping an ideal alternative. Lapping can remove the surface scale left from heat-treatment, and it re-matches two mating members by removing some runout and flank form distortions. Lapping can reduce the transmission error in many cases due to the fact that the major material removal is in the center region of the teeth, where the tooth contact under light load is expected. In order for the lapping to work well, more crowning than required in the hard-finished gearset is used in the gearset design for the soft cutting. Lapping removes about 30 percent of this crowning, such that the length and profile crowning are just right after the lapping. Soft cutting of parts that are lapped after heat treatment considers a stock allowance of .03 mm in the pinion and 0.01 mm in the gear. If grinding is the hard finishing process (for face-milled gearsets) then the design crowning is identical to the desired crowning after hard finishing. Between soft cutting and grinding, a uniform stock allowance of 0.10 mm to 0.15 mm is applied to the pinion and gear flanks.

(https://test.geartechnology.com/)

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2026 New Week FK Product Recommendation:

Pillow Block:

A pillow block bearing (or plummer block) is a mounting used to support a rotating shaft with the use of bearings and various accessories. The assembly consists of a mounting block which houses a bearing. The block is mounted to a foundation, and a shaft is inserted, allowing the inner part of the bearing/shaft to rotate. The inside of the bearing is typically 0.025 millimetres (0.001 in) larger diameter than the shaft to ensure a tight fit. Set screws, locking collars, or set collars are commonly used to secure the shaft. Housing material for a pillow block is typically made of cast iron or cast steel.

https://www.fk-bearing.com/products/Pillow-Block/698.html