Many of our customers at Industrial Sprockets & Gears, Inc. have come to us after receiving no-quotes on the projects from other gear manufacturers due to part quantity or complexity. Our team is capable of producing custom gears and sprockets in any quantity from a single piece to hundreds of parts, and our engineering and machining capabilities are unrivaled in the industry. The part shown here is a custom internal spur gear that is used in a piece of rotating equipment. The gear has an inner diameter of 100″, making it a very unusual size. To add to the challenge of this project, the gear was specified to be cut from 4340 steel, which has a Rockwell hardness of approximately 40, making the material difficult to cut. While many shops would avoid this type of project, our team is truly passionate about gear cutting and relishes in developing solutions to unique challenges.

To manufacture the spur gear, a CNC vertical turning lathe, and a Fellows Gear Ghaper machine were used. Special tooling was designed and fabricated to compensate for the hardness of the steel material. After tooling was complete the gear was cut in one week, resulting in an approximate total turnaround time of 6 to 8 weeks. The gear was produced to AGMA Class 8 standards with dimensional tolerances as tight as ±0.001″. Our rigorous in-house quality inspection program ensures that all gears meet customer specifications and applicable industry standards. The customer was impressed with the quality of the gear and the timeframe in which we were able to deliver the finished product. For additional information, about this custom internal spur gear manufacturing project, contact us directly.


Product Name

Internal / External Spur Gear

Product Description

Internal Spur Gear

Capabilities Applied/Processes

Primary: custom engineering and tooling

Equipment Used to Manufacture Part

Fellows gear shaper

Overall Part Dimensions

100” ID

Tightest Tolerances


Material Used


Material Finish

machine cut

In process testing/inspection performed

ISG inspection

Estimated Part Weight

8,000 lbs

Industry for Use

Rotating equipment

Delivery Location

Midwest, USA

Standards Met

AGMA quality #8


1 Week