Sometimes a seemingly simple redesign task can open the door to a simpler, less costly and more robust product. The key is to be willing to ask a “stupid question.” (Stupid Question: def; a question you have that you fail to ask.) No one knows everything about everything. Ignorance is easily cured by asking questions, but stupidity, unhandled, can often be fatal.
In this case, a machine that had an Arming Rod Assembly would infrequently experience a field failure when the Knob of the Arming Rod Assembly would fly off when a circuit was tripped. (It was quite unacceptable to have a Knob “flying” around an office.) The machine would be set (armed) by pushing in the Arming Rod against a rather stiff spring. When a fault occurred, a relay would release and the Arming Rod would snap out. The problem to be solved was ensuring that the Knob stopped when the Arming Rod stopped and not become a projectile. Is it possible to absolutely guarantee that the Knob would never come off in any circumstance?
The “obviously” correct answer is to make an undercut on the shaft, tightly screw down the set-screw and then add a drop of thread adhesive to boot. Or, better yet, use two set-screws, 120 degrees apart. But does that absolutely guarantee that the Knob will never come off? Unfortunately, no.
But, there is one circumstance where the answer to the original question is a resounding YES! The only way to absolutely guarantee that the Knob would never come off under any circumstance is to eliminate the Knob entirely. A Knob that is not there absolutely and positively cannot come off.
Next question was, why is it made out of brass? And then, why does it have shrink tubing on it? And finally, why do we have that expensive screw machine part on the end, made out of stainless steel no less? Getting answers to all of those questions and a few others, along with having an extensive knowledge of many different manufacturing processes, resulted in a knob, consisting of a steel bushing, plastic cap and a set screw, a turned and drilled brass rod covered with shrink tubing and a stainless steel screw machine part being eliminated. All were replaced with a single wire-form part that was ready to be installed upon receipt from the vendor.
The picture above shows the original Arming Rod Assembly and the 1-piece stainless steel wireform part that replaced it. As an added bonus, this part was “retrofitable” to existing machines being returned for refurbishment. This resulted in a running change, with no need to keep an inventory of old parts because the new part could be used on old and new machines alike.
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