Tips & Tricks - Designing Mating Parts with Rotational Symmetry

Right and left handed parts are a common occurence in machine design, where the parts are mirror images of each other. For example, this may be a sheetmetal profile folded in opposite directions, or a fabricated part using the same parts in opposite orientation. Design requirements often mean that handed parts are unavoidable, which means a greater number of parts, increased manufacturing and assembly time, and inventory storage.	Mirror Image Symmetry
However, a special case occurs when mating parts are rotationally symmetric. In the example below, the rectangular box could have been made as two separate parts - one with the latch points and the other with the hinge points. Adding one of each to take advantage of rotational symmetry eliminates the need for the second part. In other words, you could reach into a bin of identical parts, pull out any two and join them. The advantages of such self-mating design include lower tooling, setup and manufacturing costs — the parts can be made in a single mold instead of two — and lower cost of maintaining inventory. So keep an eye out for this opportunity, it's easy to miss!
Rotational Symmetry (image courtesy of Protomold) www.protomold.com
See more examples and applications of rotational symmetry here.