Keys, Keyways and Conventional Representations

Keys, Keyways and Conventional Representations

A key stops a pulley, gear or coupling rotating on its shaft. It sits in a keyway — a slot cut in both the shaft and the hub — so that torque passes through the key rather than through friction alone.

Types. A parallel (square or rectangular) key is the most common. A gib-head key has a head for extraction. A woodruff key is a semicircular disc seated in a curved slot, self-aligning on tapered shafts.

Drawing conventions. Like bolts, a key is not hatched when the section runs along its length. Keyway dimensions are given as a width and a depth, and the depth is measured from the shaft surface.

Other conventional representations save enormous drawing time by agreement rather than by accuracy:

• Springs are drawn as a few turns with a chain line through the omitted middle.
• Knurling is shown as a small patch of cross-hatching, not drawn all over.
• Repeated features — a bolt circle of twelve identical holes — are drawn once or twice fully and the rest marked by centre lines only, with a note such as "12 holes Ø8 equally spaced on Ø90 PCD".

Core checkpoint: Conventional representations are agreements, not shortcuts. A reader who knows the convention loses no information.