Terminology - Gearboxes Information

Mechanical advantage - The difference between the applied force and the work accomplished. Mechanical advantage allows machines to perform more work with less effort.

Meshing - The action of interlocking with another object. Meshing gears are used to transmit mechanical energy.

Mitre Gear - Conical shaped gears designed to operate on intersecting axes at 90 degrees. The mitre gear teeth may be straight cut or spiral cut. The faces of a set of mitre gears combine to give a 1:1 ratio at 90 degrees with both gear faces being 45 degrees. Compare bevel gear.

Nip point - The point where two gears mesh, which can pinch or crush fingers or other body parts.

Nonferrous metals - Metals that do not intentionally contain iron.

Nonmetallic materials - Materials that are not made of metal, such as wood and plastic. Nonmetallic materials can be used to make gears, though they are not as common.

Open gearing - Gears in an unassembled form.

Output shaft - The rotating shaft that receives power from the mechanical system and transfers it to the output source.

Outside Diameter (OD) - The overall diameter of the gear at the tips of the teeth.

Personal protective equipment - Safety equipment that a person wears or uses to prevent injury in the workplace. Personal protective equipment is abbreviated as PPE.

Pinion Gear - The smaller gear in a gear set, the larger one is known as the bull gear. Also, the round gear used with a rack in a rack and pinion set.

Pitch - A property used to classify gears. Pitch usually refers to the number of gear teeth in one inch of the gear's pitch diameter.

Pitch Circle - the curve of intersection of a pitch surface of revolution and a plane of rotation. The imaginary circle where the teeth of a gear contact a mating gear without slippage. See also pitch diameter

Pitch Diameter - The diameter of a gear's pitch circle. A gear's pitch diameter can be determined by measuring from the top of one gear tooth to the bottom of the opposite gear tooth.

Pitting - The corrosion of a metal that takes place in specific locations on a workpiece or component.

Plain Bearing - A bushing. A bearing with no rolling elements.

Planet arm - A moveable arm that rotates around the sun gear on which planet gears can be mounted.

Planet gear - An outer gear in a planetary gear train that rotates around the sun gear. A planet gear can be mounted on a moveable planet arm that also rotates around the sun gear.

Planetary gear train - A gear train that consists of one or more outer gears rotating around a central gear. Planetary gear trains are also known as epicyclic gear trains.

Plastic flow - A gear failure condition in which the gear teeth deform due to heavy loads.

Precipitation Hardening - An alloy strengthening method. Performed with two heat treatments that result in the growth of extremely small uniform particles. The small particles strengthen the metal.

Pressure angle - The angle made by the sides of a gear tooth as they incline toward the top of the gear.

RA - Roughness Average which is an average of the peaks and valleys of a material's surface profile.

Rack - A flat bar with teeth used with a spur gear to produce linear motion. As the spur gear turns, the rack slides in linear motion.

Ratio - The number of revolutions per minute of the input shaft in relation to the number of revolutions per minute of the output shaft.

Reduction - A lowering of output speed in relation to input speed.

Right Angle Gearbox - A gearbox designed to transmit motion between two shafts at a 90 degree angle.

RMS - Root Mean Square is an alternative method of measuring the surface roughness. The value for RMS is generally about 10% higher than the RA value for the same surface.

Root Diameter - The diameter of a circle measured across the valleys of opposing teeth.

Rotary Motion - Movement around a shaft as distinct from linear motion which is movement along a shaft. Most common gearboxes convert rotary motion into rotary motion at a different speed or in a different direction. However gearboxes can be designed to convert rotary to linear, linear to linear or linear to rotary motion.

Servo Rated - Suitable for use with a servo motor.

Tolerance - The permissible limit of variation from the nominal size. For example an 8mm shaft may be represented as 8.000 mm +0.000 / - 0.008 which would mean that the actual shaft size may be anywhere from 7.992 and 8.000 mm.

Spiral Teeth - Curved teeth cut into a bevel or mitre gear.

Spur Gear - A gear with equally spaced straight cut teeth around it's outside surface designed to mate with another gear of equal pitch placed on a parallel shaft.

Tee Gearbox - A gearbox designed to transmit motion from a single input shaft to two shafts mounted at 90 degree to the input shaft. The two output shafts extend in opposite directions forming a "T" with the input shaft.

µm - Micron or thousandth of a millimeter (0.001mm).

Wear - The gradual removal of material from the contact between mating parts.

Worm - A cylindrical screw used with a worm gear to transmit motion. Each full revolution of a single lead worm will turn a matching gear by 1 tooth distance.

Worm Gear - A gear with teeth that mesh with the threads of a worm to transmit motion.

Worm Drive - A gearbox utilising a worm and worm gear. Transmits motion between nonintersecting perpendicular shafts (cross axis). These boxes can usually transmit very high torque and large speed reductions.

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