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Gears

  2026-03-17

  Edited: 2026-03-21

Apparently there is a lot that goes into gears. I was mislead by Minecraft Create mods that the only thing you care about was gear ratios...

Involute Gears

Gears are supposed to roll and not slide, non-involute gears will cause them to slide. This is more commonly referred to as your gears "sliding". Sliding is bad because it is inefficient, think of gears as wheels; the purpose of wheels is to roll, by rolling they have less contact point with the ground and therefore less friction. Between sliding (dragging) a wheel or rolling it, which is easier? Obviously rolling it, the same principle applies for a gear.

Unfortunately, gears are kind of complicated to make. The Solidworks toolbox gears are non-involute. Do not use them in production! Those gears are only for display and placeholders. See the grabcad link below for a Solidworks part which allows you to generate involute gears.

Note that involute gears should be used for gear to gear, but for rack and pinion, only the pinion should be involute. It is fine for the rack to be flat and nont involute. See the wikipedia article.

References:

Gear Configuration

In the metric system, module is used to describe gears. The module is the ratio of the reference diameter (or pitch diameter) of a gear divided by its teeth. In the imperial system, diametrical pitch (DP) is used instead. DP is the total number of teeth divided by the pitch diameter (in inches). You can convert between module and diametrical pitch via

\begin{equation} \text{Module} = \frac{25.4}{\text{DP}} \end{equation}

A lower DP (higher module) means the gear is able to handle more torque, while a higher DP (lower module) means the gear is able to run more efficiently (more quiet so less energy is wasted on vibrations).

More teeth helps a gear run smoother, but of course will increase the size and potentially cost of the gear.

References:

Gear Ratio

Gear ratio is the ratio of the number of teeth on the output gear to the number of teeth on the input gear. The input gear is referred to as the pinion, while the output gear is referred to as simply the gear. For example a 2:1 ratio means the pinion turns at twice the speed of the gear. A small pinion and big gear increases the torque at the cost of speed, while a big pinion and small gear increases the speed at the cost of torque.

For multiple gear ratios in a row, you can find the total ratio by multiplying the ratios together.

References:

Shafts

There are many ways to mount the gear to a shaft

In general, keyed shafts are used quite often in the industry as they are fairly strong and quite cheap to make. I have not seen much of keyed shafts in 3D printing, likely because the filaments are generally not strong enough to sustain shear under high torque. I guess that is why hex shafts are used more often, as they are better in regards to torque, though not as much as spined shafts, but these are hard to make. In particular, hex shafts are used when loads can damage the key.

Important: print shafts horizontally otherwise the print layer are parallel to the shear and will destroy the shaft instantly.

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