Worm Measurement Over Pins Calculator

Worm Gear Measurement Over Pins (or Measurement Over Wires) is a method for measuring and inspecting worm gears. Pins or ball bearings are placed opposite each other in the thread of a worm and calipers are used to measure the distance across them. For worm gears, three pins or balls are used: two on one side, one on the opposite side. For odd-start worms (1-start, 3-start, etc.), the two balls on the same side can be in adjacent threads. For even-start worms (2-start, 4-start, etc.) the set of two balls should be separated by a thread.

Information about the wormgear is also required to determine the axial pitch (the distance from one point on the thread to the same position on the next thread) of the worm. The axial pitch of the worm matches the circular pitch of the wormgear.

We built this gear measurement over pins calculator as a useful tool for designing and checking gears in our own shop, and want to share it with other gear enthusiasts around the world. This calculator ensures the tooth thickness on your worm gear is the right size using pins commonly found in your machine shop or easily ordered online.

How to Do Measurement Over Pins on a Gear

  1. Input your gear parameters
  2. Find the recommended best pin to use
  3. Choose and input your pin size, as close as practical to the best pin
  4. Axial backlash is optional – adding backlash decreases tooth thickness
  5. Calculate correct measurements to check your gear
  6. Enter your measurement to calculate the difference in worm tooth thickness
  7. See results, formatted for easy copy and paste into Excel
  8. Measure your gear across any pair of furthest-apart teeth (closest to 180º)


Results conform to ANSI/AGMA 2111-A98 reaffirmed in November 2020

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Note: Standard pins are not required (like the 1.728 or 1.92 series Van Keuren pins) — any set of quality high precision and known diameter pins that are close to the best pin diameter will work.

As the test pin diameter differs from the "best pin," the intersection with the worm shifts off the pitch diameter, and the target measurement differs

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Worm Measurement over Pins (aka Measurement over Spheres)

"Measurement over Pins" and "Measurement over Spheres" are interchangeable terms when it comes to measuring gears, due to the many similarities between gears and threads. Using a precision pin allows for accurate and efficient measuring of gear teeth. Since a gear tooth is curved along its entire length (it follows the involute profile of a circle) it becomes incredibly difficult to measure.

By introducing known-sized circular pins, the measurement becomes easy but requires some math. Fortunately, we've coded the math once so we (and you) won't need to touch it for each measurement.

Gear Measurement, Design, and Production | Evolvent Design

We've been working with gears for decades and have done everything from gear design and specification, measurement and inspection, custom repairs, and small-to-mid sized production runs. We're a small shop but have extensive experience and the machinery for prototyping and small-scale production in-house. We've built tools like our Gear Measurement Over Pins Calculator to help us, and others, through every stage of the gear design process.

Looking to replace a broken gear, or design a new one from scratch? Want to understand more about Addendum Modification, Contact Ratio and the design of quieter gears? We can help — Contact Us today to get your product started

Here's a Quick Summary:

› Input your gear parameters

› Choose an appropriate pin size

› Measure the size of your gear