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Keys and keyways are old-school mechanical engineering, but they are still common in shafts, couplings, pulleys and gears. A good keyway design must transmit torque without creating an avoidable weak point in the shaft.
What the Key Does
The key transfers torque between the shaft and the mounted component. The shaft, key and hub therefore work as one load path.
Watch the Shaft Strength
Cutting a keyway removes material from the shaft and creates a geometric discontinuity. The keyway can become a stress concentration, especially in highly loaded or fatigue-sensitive shafts.
Use Standard Sizes
Standard key and keyway dimensions make manufacturing and replacement easier. Avoid inventing a custom key size unless the application genuinely requires it.
Check the Hub Too
Designers sometimes calculate the shaft and forget the hub. The hub must have enough material around the keyway and enough engagement length for the transmitted torque.
Drawing Checklist
Specify shaft diameter, keyway dimensions, key size, length, material where needed and any fit requirements. Clear drawings reduce questions on the shop floor.
Keep learning: Explore more practical engineering articles in the GetCADFile Design Guide.