Resources · Terminology
Glossary
63 precision-transmission terms, plain-language definitions.
If you're writing an RFQ for a part you've never specified before, or you're reading an inspection report whose acronyms are new, this is the page to bookmark. Each entry is short and skips the textbook detour.
Last updated Reviewed by Luo Genwen, Production Plant Manager
A
3 terms
- The radial distance from the pitch circle to the tip of a gear tooth. Usually equal to one module on a standard gear.
- American Gear Manufacturers Association. Publisher of US gear-quality standards (e.g. AGMA 2000-A88 and the newer AGMA 2015) and load-rating standards.
- Surface treatment that grows an oxide layer on aluminum parts for corrosion resistance, hardness, or color. Common on aluminum timing belt pulleys.
B
3 terms
- The clearance between mating gear teeth, measured along the pitch circle. Too much causes positioning error; too little causes binding and overheating.
- A gear with conical pitch surfaces, used to transmit motion between intersecting (usually 90°) shafts. Spiral-bevel and straight-bevel are the two main variants.
- A controlled-rust surface treatment producing a thin dark layer for mild corrosion resistance and aesthetic finish. Common on steel transmission parts.
C
6 terms
- A heat-treatment process that diffuses carbon into the surface layer of low-carbon steel, then hardens it. Produces a hard wear-resistant case over a tough core.
- The depth from the surface to which a part has been hardened by a case-hardening process. Specified in millimeters and measured on a hardness traverse.
- The distance between the rotational axes of two meshing gears. Drives the kinematic design of any gear pair.
- Coordinate Measuring Machine. Uses a touch-probe to measure dimensional features on a part. Wolfer's envelope: Ø 0–800 mm.
- The average number of tooth pairs in contact during one mesh cycle. Higher values produce smoother motion and lower noise.
- A device that connects two rotating shafts to transmit torque. May be rigid, flexible (jaw, diaphragm, bellows), or torque-limiting.
D
3 terms
- The radial distance from the pitch circle to the root of a gear tooth. Slightly larger than the addendum to provide tooth-tip clearance.
- The number of gear teeth per inch of pitch diameter. Used in imperial gear specifications; the inverse concept of module.
- Deutsches Institut für Normung — the German national standards body. DIN 3962/3963 is the German gear-tolerance standard widely used by European OEMs.
E
1 term
- European standard for material inspection certificates. A "3.1" certificate is issued by the manufacturer's authorized inspection authority. Wolfer ships 3.1 certificates by default.
F
3 terms
- The axial length of the gear tooth, measured along the pitch cylinder.
- Finite-element analysis. Numerical simulation method used to validate bending stress and contact stress on heavily loaded gears before first cut.
- The working surface of a gear tooth between the tip and the root, where contact with the mating tooth occurs.
G
2 terms
- The ratio between the number of teeth on the driven and the driving gear. Determines the speed and torque relationship across the pair.
- A finishing operation that removes small amounts of material to achieve final dimensional accuracy and surface finish. Wolfer uses YK7236 / YK7250 grinders for ISO 1328 Class 5 accuracy.
H
4 terms
- Resistance to localized plastic deformation. Specified on the Rockwell (HRC), Vickers (HV) or Brinell (HB) scales depending on the material and depth.
- Controlled heating and cooling cycle that changes the metallurgical structure of a part. Carburizing, nitriding, induction hardening and quench-tempering are the most common methods.
- A cylindrical gear with teeth cut on an angle (helix angle) to the axis. Smoother and quieter than a spur gear at the cost of axial thrust.
- A gear-cutting process using a hob (a worm-shaped cutter) that generates teeth by continuous rolling action. Wolfer hobs up to module m12.
I
4 terms
- A localized heat-treatment process that uses electromagnetic induction to heat a part's surface. Suitable for journal bearings and selectively hardened gear teeth.
- A gear with teeth cut on the inside of a ring. Meshes with an external gear (pinion) inside it; used in planetary reducers and ring-gear drives.
- The standard tooth-profile geometry used in modern gears. Maintains a constant velocity ratio and tolerates small variations in center distance.
- International gear-accuracy standard. Classes 0 (highest) to 12 (lowest). Wolfer routinely produces Class 5–8.
J
1 term
- Japanese gear-accuracy standard, used by Japanese OEM customers and their Chinese subsidiaries. Maps closely to ISO 1328.
K
2 terms
- A commercial gear-design and calculation software. Wolfer accepts KISSsoft design output as a manufacturing input for non-standard module or pressure-angle gears.
- German manufacturer of gear-inspection and bevel-gear-cutting equipment. The "Klingelnberg-type" gear inspection center at Wolfer measures pitch, profile, lead, and runout in one setup.
L
2 terms
- Deviation of the actual tooth-trace from the theoretical line across the face width. One of the four core parameters on a gear inspection report.
- A shaft-hub connection that uses a wedging or shrink action (taper bushing, shrink disc) to grip a shaft without keys. Eliminates backlash.
M
2 terms
- A document from the steel mill stating the chemical composition and mechanical properties of a batch of steel. Wolfer ships EN 10204 3.1 certificates by default.
- The pitch diameter divided by the number of teeth. The fundamental sizing parameter of a metric gear. Wolfer hobs up to m12.
N
1 term
- A surface-hardening heat-treatment process that diffuses nitrogen into the part. Produces a very hard case with low distortion — suitable for precision gears that cannot be ground after heat treatment.
P
7 terms
- The smaller of two meshing gears. In a rack-and-pinion drive, the pinion is the rotating gear that engages the linear rack.
- The theoretical circle on which the kinematics of a gear are defined. The point of contact between two meshing gears is on the pitch circle.
- The diameter of the pitch circle. The product of module × number of teeth (metric) or number of teeth ÷ diametral pitch (imperial).
- Deviation of the actual tooth spacing from the theoretical spacing. One of the four core parameters on a gear inspection report.
- The angle between the line of force on the tooth and the tangent to the pitch circle. Standard values are 20° (most common) and 14.5°.
- Deviation of the actual tooth flank from the theoretical involute curve. One of the four core parameters on a gear inspection report.
- A deliberate radial offset of the gear cutter from the standard position, used to avoid undercut on low-tooth-count pinions or to fine-tune center distance.
Q
1 term
- A two-step heat-treatment process: rapid quenching to harden, then tempering at a lower temperature to relieve brittleness. Used for through-hardened transmission components.
R
3 terms
- A linear gear — effectively a gear of infinite radius. Meshes with a pinion to convert rotary motion to linear motion. Wolfer's racks reach module 12 and lengths over 2 m.
- The total indicator reading of a rotating part. For gears, the radial runout of the pitch circle is one of the four core inspection-report parameters.
S
8 terms
- A gear made by compressing metal powder and sintering it. Lower precision than cut-and-ground gears; common in low-cost consumer applications. Not a Wolfer product line.
- A bevel gear with curved teeth. Smoother and quieter than a straight-bevel gear at the cost of more complex cutting machinery.
- A shaft with longitudinal ridges that mate with corresponding grooves in a hub. Transmits torque without slip and allows axial sliding.
- A cylindrical gear with teeth parallel to the axis. The simplest and most common gear type.
- A toothed wheel that engages a chain. Used in chain drives where positive engagement (no slip) is required.
- A corrosion-resistant steel alloy containing chromium. Common grades for Wolfer parts: SUS304 (general), SUS440C (high hardness), 17-4 PH (high strength).
- A measure of surface texture, specified by parameters such as Ra (arithmetic average) and Rz (peak-to-valley). Measured with a contact profilometer; Wolfer uses Mitutoyo SJ-410.
- A toothed pulley designed to engage a toothed (timing) belt. Provides positive engagement at high speed without slip.
T
6 terms
- A locking-assembly variant where a tapered split bushing is wedged into a tapered hub bore by axial screws. Compact and reusable.
- A toothed belt that engages a synchronous pulley. Provides positive engagement without slip; common in linear motion stages and printing machinery.
- A designation indicating the precision grade of a manufactured feature. For gears: ISO 1328 Class 0–12, DIN 3962 Class 1–12, AGMA Q1–Q15.
- A coupling that disengages or slips when a preset torque is exceeded, protecting the driveline from overload. Available in friction or ball-detent designs.
- The width of a gear tooth measured along the pitch circle. Controlled tightly to achieve specified backlash.
- A part that has been heat-treated to a uniform hardness throughout, rather than a hardened case over a softer core. Used where moderate hardness and high toughness are both required.
W
1 term
- A gear set consisting of a worm (screw-like driver) and a worm wheel. Produces high reduction ratios in a compact envelope but with lower efficiency than helical sets.
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