2023 ASEE Annual Conference & Exposition

The purpose of this paper is to make it easier for beginners to design keyed joints, primarily in machine design courses. End-milled profile keyseats are apparently simple features. Even so, in teaching this topic, some points are challenging; these include how to assume a reasonable keyseat fillet radius, how to account for notch sensitivity, and whether keys fail due to shear or compression. Moreover, because keyed joints involve disparate topics—static failure, fatigue failure, stress concentration, engineering graphics, and manufacturing—beginners benefit from having these topics addressed together.
This paper offers the following main recommendations:
• Account for shaft curvature when dimensioning a keyseat.
• Specify fillet radii based on sizes of bull nose end mills. Chamfer keys.
• Neglect notch sensitivity in shaft fatigue calculations.
• Size keys based on compression failure formulas, despite keys typically failing in shear.
These recommendations may differ from guidance in textbooks and standards—but they are better grounded in the evidence and offer the clarity needed for design calculations.
In addition to literature review, this paper reports novel finite element analysis of key failure, showing that large fillet radii do not compromise key strength, which is complex and dominated by shear. Because tight fillet radii weaken the shaft, larger fillet radii are recommended. Those points would lead to shafts that are more economical to produce and less likely to undergo fatigue failure, without compromising key strength.