Gear Speak: A Guide to Gear Language, Part 2

In our first part of “Gear Speak”, we covered the key terms that describe a gear’s physical characteristics. Now that you are an expert on that subject, we can get to the good stuff: the words related to the interaction between two or more gears.

Before we fully dive in, let’s quickly consider how and why gears function. Simply stated, gears are used to transmit both motion and power between components. They generally operate on the principle of mechanical advantage through the interlocking of toothed wheels. They may allow for torque and speed conversion and/or direction changes as well.

Gear types and configurations vary as vastly as the applications that require them, so it’s important to have a good understanding of the following gear-related terms when specifying:

Meshing Gears – when two or more gears with teeth engage with each other to transmit power or motion. The gears must have the same pitch and pressure angle, which is a design feature that strengthens the gear. 20° is the industry standard, and PIC’s as well, but it does vary.

Backlash – the amount of clearance, or space, between two mating gear teeth. Often referred to as the “slop”, you can also think of it as the amount of play between the teeth of the gears. Every gear needs some sort of backlash in order to mesh and for the system to function.

Anti-Backlash – as the name implies, this refers to the elimination of backlash. Anti-backlash gears are used in applications that require extreme precision and accuracy. All anti-backlash configurations have two independent gear halves that are connected with springs that apply opposing force once in tension. This tension reduces the wiggle, or backlash of what a standard gear would experience.

Whole Depth – refers to the total depth of the tooth from the top to the root of the tooth.

Backlash Class – this designation indicates the clearance range as either class A, B, or C, with C being the most common.

Clearance – In mesh, this represents the distance between the top of the gear tooth to the root of the pinion gear tooth.

Precision Motion – for certain applications such as lab equipment or a laser imaging system, tight and precise control is required for proper operation. For instance, when adjusting a microscope, if the input gear moves .25°, the output has to move the exact same amount.

Gear Ratio – is the numerical relationship between two mating gears based on the number of teeth and the number of rotations it takes the secondary gear (pinion) to make one full rotation in relation to the main (driven) gear.

Helix Angle – The angle at which the gear teeth are cut to the axis of rotation. Gears can be cut with a right-hand or left-hand helix angle. Right-hand gears will only mesh with left-handed parts.