Spur & Helical Gear Measurement Over Pins Calculator
Measurement Over Pins (or Measurement Over Wires) is a method for measuring and inspecting spur gears and helical gears, with both even and odd tooth counts. For finding size measurement spanning across a fixed number of teeth, you can find these measurements using our Gear Span Measurement Calculator and a good set of calipers for most spur gears. Balls are required for Internal and External Helical Gears.
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 spur gear or helical gear is the right size using pins commonly found in your machine shop or easily ordered online. Standard micrometers work for the 2-pin spur solutions. Disc or flange micrometers and 3 wires or pins will make the task easier for helicals.
How to Do Measurement Over Pins on a Gear
- Input your gear parameters
- Find the range of acceptable measurement pins
- Choose and input your pin size
- If you're measuring a helical gear, subscribe on Patreon then enter the access code (Spur gears are still free)
- Calculate correct measurements to check your gear
- See results, formatted for easy copy and paste into Excel
- Measure your gear across any pair of furthest-apart teeth (closest to 180º)
Results conform to ANSI/AGMA 2002-D19 published in December 2019
The default Manufacturing Profile Shift Coefficient is 0. Positive values result in thicker teeth, as if your cutting tool did not cut to a full depth, while negative values result in thinner teeth. Minimum pin size ensures your pin protrudes beyond the tip of the gear teeth, allowing it to be measured with standard instruments.
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 will work that are within the range we calculate above.
Measurement over Pins (aka Measurement over Wires)
"Measurement over Pins" and "Measurement over Wires" 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. For finding the outer diameter of your gear blank before the teeth are cut, you can use our Gear Dimension Calculator to find the key dimensions of your spur gear pre-production .
Measurement over Pins for Helical Gears
Measurement over Pins can also be done to inspect helical gears with the same process as spur gears, but with more complex calculations. The gear parameters will determine the range of acceptable balls for inspection, and once a bal size is selected, the target value is calculated. Helicals require balls instead of pins due to their complex geometry. Note that a new plane is defined when using helical gears, it is defined as the transverse plane. Helicals have both a normal and transverse plane, and thus both have a normal and transverse diametral pitch. Manufacturing Note: the hob diametral pitch will match the normal diametral pitch measured on the normal plane.
In order to support continued development and upkeep, calculating the MOP for helical gears requires a subscription to our Patreon page (at the "Helical Gear" tier or higher). You'll receive an access code that unlocks this feature, as well as .STL downloading from our .STL Generator (in addition to all of the extra content on Patreon and early access to videos!)
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