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3D Printed Gears – Get the Gear That Fits Your Needs

Picture of David Pechter
by David Pechter
Nov 17, 2018

Gears are a great thing to 3D print! Gear designs are surprisingly complicated, but with the right tools, models, and materials, you'll soon be on your way.

3D Printed Gears Becoming a Gear Head

A spur gear.
A spur gear. Source: hswstatic.com

Gears look cool and are clearly fun. But how do they work, and what are they used for? Gears use meshing teeth to transform rotation. When gears are the same size, they transfer rotation from one gear center to another. When the gears differ in size, something else happens: there is a transformation from slow and strong to fast and weak.

The key: One tooth of rotation on one gear is matched by one tooth of rotation on its mate.

Consider a 15-tooth gear meshing with a 60-tooth gear. A ratio of 60/15 equates to a gear ratio of 4. Put a motor on the small gear’s shaft, and the small gear turns 4 times before it feeds the 60 teeth needed to turn the big gear once. The result is the larger 60-tooth turns 4 times more slowly, and has 4 times more mechanical advantage. Thus, speed is traded for torque, or rotational force.

3D printed gears are easy to prototype, but well-functioning gears critically depend on some key parameters. With some testing, planning, design, and attention to detail, you’ll soon be on your way.

3D Printed Gears Tip #1: Plan

A printer test.
A printer test. Source: David Pechter / All3DP

Test your Printer

Try this gear test print to see what the smallest tooth gear is that you can accurately print. Remember to use the same material that you’ll use for your gears. Diametral pitch, or simply pitch, is the number of teeth that fit on a 1″-diameter gear.

Size matters

Once you know how small you can go, you should also figure out how big you can go. Bigger gears allow bigger teeth at the same ratio. Bigger teeth are stronger and can better handle tolerance errors or movement under load.

On the other hand, big gears are also heavy, slow to print, and, well, big! Your printer, or your overall size limits, may determine the largest gear you can design in.

Know Your Inputs and Outputs

A few rules of thumb

  • Bigger is better for printing accuracy and strength.
  • For 20-degree pressure angle gears have no fewer than 12 teeth on your smaller gear.
  • For gear ratios greater than 5:1, consider a two-stage gear set.

With all this in mind, you can now start to pick gears and create a layout.

3D Printed Gears Tip #2: Don't Reinvent the Wheel

Involute action.
Involute action. Source: Wikimedia

Start with online designs that have 100 years of know-how built in. Involute spur gears are shaped to create a continuous rolling mesh. Their theoretical pitch diameter, set approximately at one half the height of the teeth, represents a mathematical surface where two mating gears appear to roll on one another. This rolling action applies to two gears of any size as long as they meet these four key requirements:

  1. Mating gears are spaced so that their pitch diameters are tangent (or nearly so). The distance between two gears = (0.5 * sum of their pitch diameters) + breathing space. This breathing space is extra spacing to ensure free rotation. For 24p gears, it’s about .003″, while larger gears will need around .005″.
  2. The gears need to have the same pitch (tooth size)
  3. The gears need to have the same pressure angle (tooth shape). Gears with mismatched pressure angles can run fine at first but will quickly start to shred each other.
  4. The face widths (the thickness of the gears) should roughly match to make the best use of the material.

Tip: In a pinch, you can scale your gears at the slicer to make slight changes needed in center-to-center distances. Just don’t forget to use the same scale for all gears to maintain the same pitch.

3D Printed Gears Tip #3: Materials Matter

Gears can fail.
Gears can fail. Source: Wikimedia

Nylon is the first choice for durable gears, especially for running without lubrication. Nylon has the lubricity, strength, and flexibility required to make a long-lasting plastic gear. Taulman PCTPE, Bridge, or 910 filaments, for example, all work well depending on your application.

Given that nylon is very hygroscopic, pre-drying is always recommended before printing. To save on hassle, PLA or ABS are good second choices.

Keep in mind that 3D printed plastic is not nearly as strong as aluminum or steel. You’ll want to consider this when you decide how to apply torque to your gears. Two options are to mold in features that match your shafts or build your own hub using hex shafting. Keeping shafts, keys or hex features as large as you can will also help ensure that you can reliably transfer the force you need.

3D Printed Gears Online Generators and Repositories

Image of: Online Generators and Repositories
Source: Gear Generator

Once you have a basic design in terms of ratios, pitch, and overall size, gear generators give you the ability to customize your design:

Downloadable gear designs are a good place to start:

License: The text of "3D Printed Gears – Get the Gear That Fits Your Needs" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.

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