Monday, April 15, 2013

Breakaway Design

In August 1991, I traveled with friends to Dorrance, Kansas and met Tom Mahoney who was manufacturing a breakaway basketball goal which he invented. It was a neat idea and prevented a lot of glass shattering.  I suppose it impressed me enough that I regularly consider fail-safe points in the design phase of a lot of projects.

I was reminded of the subject when a friend was helping me close up the studio a few days ago.  We were preparing to run the tumbler for 20 minutes after we left.  When I turned on the machine there was a loud noise as it started to rotate so I shut it off.  My friend had forgotten to move away a support which I use to prop up the near-side door so it serves as a shelf for unloading.

When I built the support it occurred to me that exactly this sort of thing could happen.  If the support could not give something catastrophic might happen.  To provide the fail safe the top cross arm is attached only with four tack welds and the actual catch is only a flimsy piece of strip.  The design worked perfectly.  On the first revolution the hinge on the tumbler struck the cross arm and it bent down hinged on two of the tack welds to the point where it was clear of obstruction.   The next morning I repaired it.

There isn’t anyway to know for sure how strong a thing is other than breaking it but some pretty good guesses are possible.  In the final analysis it’s probably more useful to know that breakage will occur in a safe way than to know exactly how much force a thing can endure.

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