Key (engineering)
Set screws often accompany parallel keys to lock the mating parts into place.
The purpose of the taper is to secure the key itself, as well as to firmly engage the shaft to the hub without the need for a set screw.
The problem with taper keys is that they can cause the center of the shaft rotation to be slightly off of the mating part.
This limited shear strength specification is designed to sustain normal operation, but then give way in the event of excessive shaft torque, thus protecting the rest of the machine from damage.
Introducing an additional bushing component between hub and shaft improves the performance and convenience of keyed joints.
By simply driving setscrews into selected holes, the hub mechanism conveniently operates to rigidly lock or definitely release from the shaft, without hammering or hub-pulling.
What would have been the side of each keyway forms heels against which the key sits, and transfers force compressively.
This latter point means that for reversible motion of the shaft, another key along a tangent outwards in the opposing direction is needed.
The specific broach, bushing and guide are used for each given keyway cross-section, which makes this process more expensive than most of the alternatives.
Finally, shims are placed between the bushing and the broach to achieve the correct depth necessary for the key.
Another difference is a keyseater has a guiding system above the workpiece to minimize deflection, which results in a closer tolerance cut.
[7][8] Wire-cut electrical-discharge machining (EDM) is primarily used for small production lot sizes where either extreme precision is required or other cutting technologies are not readily available.
[9] Shaping or slotting is largely used for cutting keyways that do not extend through the full length of the part.
[11] A shear key is a feature intended to fail and avoid further damage should the machinery be accidentally operated in excess of its design limits.
The shear key is easily and inexpensively replaced, and avoids more serious damage to the mechanism that would be costly or difficult to repair.
When excessive torque is applied to the joint, the steel edges shear the brass key into two pieces, leaving the pulley spinning loosely on the shaft and relieving the rest of the machine from possible damage.
[3] Improperly machined keyways that had cutter deflection or drifting occur, may not be strong enough for the required application.
