Spur vs. Helical Gears: When to Specify Each

Spur and helical gears are the two most common parallel-axis gear types, and the choice between them is one of the first decisions in a drive design. Both transmit power between parallel shafts; the difference is the orientation of the teeth, and that single difference cascades into noise, load capacity, and thrust.

Spur gears

Spur gear teeth run parallel to the axis of rotation. Each tooth engages across its full face at once, which makes them simple to manufacture and inspect and produces no axial thrust. The trade-off is that the sudden full-width engagement generates more noise and vibration as speed increases. Spur gears suit lower-speed drives, intermittent motion, and applications where axial thrust must be avoided.

Helical gears

Helical teeth are cut at an angle (the helix angle) to the axis. Engagement begins at one end of the tooth and progresses smoothly across the face, so more than one tooth is always in contact. This gradual engagement gives helical gears quieter, smoother operation and higher load capacity than an equivalent spur gear. The cost is an axial thrust force generated by the angled teeth, which the surrounding design must absorb with thrust bearings, and a small efficiency loss from sliding.

How to choose

• Choose spur for lower-speed drives, intermittent motion, or where no axial thrust can be tolerated.
• Choose helical for high-speed gearboxes, high load capacity, and low-noise requirements such as robotics, servo drives, and continuous-duty machinery.

Manufacturing both to precision

INSCO manufactures both spur and helical gears, hobbed and finish-ground to AGMA 15. Helical gears require helix-capable hobbing and grinding, and ground tooth flanks are what allow a helical gear to deliver its full low-noise, high-accuracy potential. Whichever type your application calls for, the controlling factors for performance are the same: profile, lead, and pitch accuracy, verified by analytical inspection.