Gear Tooth Profiles: Gear Gauge Identification Chart | Evolvent Design

Gear Tooth Profiles: Gear Identification Chart

Andrew Prestridge | July 21, 2022

Understanding Gear Profiles

Gears come in a wide variety of shapes and sizes, many of which look awfully similar. The difference might not look like a lot, but gears of different pitches (or modules) will not run on each other! The same goes for gears of different pressure angle (although at a small pitch, you might get away with it for a little while). To help solve this identification crisis, we've created a chart of gear tooth profiles.

How Do I Check my Gear Profile?

The gear identification chart is designed to help you identify an unknown gear, even if only a few teeth remain intact. The chart has templates for:

  • Diametral Pitch gears from DP8 to DP48
  • Module gears from Module 3.00 to 0.40
  • Pressure angles of 14.5º and 20º for both module and diametral pitch

We've created a downloadable gear template to identify the pitch, module, and pressure angle of your gears

The chart includes true-to-scale copies of all the common pitch and module sizes in both 14.5º and 20º pressure angles.

Note: while the preview image is not to scale, the downloadable PDF certainly is!

Using a Gear Tooth Gauge

A gear gauge has the gear tooth profile for one or more gears. By comparing the known gauge to an unknown gear, you can determine the gear's pitch (or module) and pressure angle. Some gear pitch gauges are metal and can run against a gear, while some are paper and allow for visual comparison.

How to Reverse Engineer a Gear

We've made a video where we walk through our steps for identifying an unknown gear. One of the simplest, and sometimes most impactful tips is in counting the teeth on the gear. Use a Sharpie to mark each tooth with a dot as you count it, and then mark every 10th tooth with a dash. This simple move helps keep the count on-track and avoids skipping or double-counting.

Counting teeth isn't hard, but in a well-made gear all teeth should look nearly indentical. Combined with a high tooth count, or small module (tiny gears), it gets easy to miscount and end up making or buying the wrong gear.

Find, Compare, and Buy the Gear
Cutting Tools You Need to Mill Gears

Using an involute gear cutter to mill a gear

How to Make a Replacement Gear

Once you know what your gear is (tooth count, pitch/module, and pressure angle) you have all the information required to make a replacement gear. Fortunately, involute gear cutters have the tooth geometry in the actual cutter, so you don't need to worry about the complex curvature – just getting the right cutter.

We supply a wide variety of involute milling cutters for both Diametral Pitch and Module gears in both 14.5º and 20º pressure angles. We recommend checking out our gear cutter database to find precisely the cutter you need to make your replacement gear (or any gear you need!)

Gear Identification Chart

Works with Diametral Pitch and Module

Templates are provided for both metric (Module) and imperial (Diametral Pitch) gears

Includes 14.5º and 20º Pressure Angles

14.5º and 20º are the most common pressure angles for nearly every modern gear

Equations and Guides

The reference chart includes the most common equation for reverse engineering gears

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