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Posted by David Sherman on Friday, May 16, 2008 at 17:36:14 :

In Reply to: Re: Digital vs dial posted by Kevin in Ohio on Friday, May 16, 2008 at 14:22:35 :

Most of the new engineers have never really built anything. A "lab" class in college consists of building a computer simulation. They think if they can draw it in autocad, you can make it exactly like they drew it. I once worked with a whiz-kid optical engineer. The company thought they'd really scored when they hired him away from the competition. He designed this intricate little blob of clear plastic that had several lenses and other optical elements molded into it. I was responsible for the electronics, which consisted of beaming a light into one part of it and detecting the light that bounced off an external object and came back into another part of it. I asked him "How much light will bounce around inside this thing and end up back at my detector when there's nothing in front of the gadget." With a straight face, he said "zero", and then proceeded to show me his computer simulation with lines showing where all the rays of light would go. I'm no optical engineer, but I knew that if you shine a light into a blob of plastic, no matter what shape it is, a little bit of lights going to come out anywhere. I tried to argue with him but he insisted that since the simulation said "zero", the answer was "zero". I had to design a custom chip for the electronics and it wasn't going to be done until his fancy lens was done, and there was no way to prototype the lens, which also had a long lead time for its tooling. I more or less pulled a number out of the air for how much light would come out the wrong way. It wasn't much, something like 10 parts per million, but it was enough that if I didn't account for it, the circuit wouldn't work. Sure enough, when the lenses came back, there was indeed light coming out the wrong way. I seem to remember it was about twice what I'd guesstimated, but it was close enough that I could deal with it. Then came the other problem. He didn't realize that plastic shrinks when it cools. The tool and die maker at the lens company could work some magic into the mold cavities to compensate for it if they could be very careful about the molding temperature and pressure, but it took a huge amount of futzing and lots of wasted parts before they got it anywhere near to what it needed to be. That engineer was one of those who thought that if he could draw it on the computer to a .00000 tolerance, it was somebody else's fault if the vendor couldn't make them to .00000 tolerance.

It must be very frustrating having to deal with prints drawn by such ignorant engineers. I suppose of you're a job shop and the only person you can talk to about it is the purchasing agent, it's easier to just try to make the thing as specified than to get the original designer to ECN in. One thing I liked about working for Fluke in the old days was that they did all their fab for everything -- sheet metal, transformers, circuit boards, plastic molding, integrated circuits, etc -- in house, which meant it was easy to talk with the people who would actually make the thing and learn what we could do to make it easier to build.



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