It’s both horrifying and fascinating. And there’s no way to learn except by shopping. Bugs = buying the wrong thing.
Conversation
I spent an hour this morning with calipers first figuring out, then buying... nuts and bolts. And there’s a chance I got it wrong.
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The polarity of build vs buy decision-making has flipped in the last 30 years. There’s really no such thing as pure building anymore. It’s all degrees of buying. A “from-scratch” design really means “from commodity COTS” — the baseline is not unrefined raw materials but China.
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I didn’t realize how utterly bad I was at this part till I tried doing non-trivial amounts of shopping in the last few months.
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Example: a typical early mechanical engineering class is called kinematics of machinery. It’s applied geometry. You work a lot of problems about how one thing will move if another moves. The things are connected by pins, sliders etc. In the textbook, the pin is just a point.
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In practice... buying a pin is a whole production. Took me hours of googling and Twitter questions to even shortlist the types of pins to choose from, and finding a cheap source of a sufficiently varied assortment box so I have room to experiment.
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And now my whole initial design is junk because I thought pin selection would be trivial. Now it is the driving constraint around which the rest of my design is developing.
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In fact I suspect “purchasing inertia” drives a lot of design. Selecting, characterizing, calibrating, and testing a catalog part is so much work that you will reuse that part in future designs until you’ve amortized the purchasing decision overhead.
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I suspect, if you’re a part supplier, making it brain-dead easy to choose your part for a large, cheap, low-end application class buys you very loyal future customers for higher-end versions.
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Replying to
JameCo is great especially if you're in the Bay Area because you can pick up/exchange at their service window (though you can't browse the warehouse). Their grab bags can help you figure out what you need when you don't know: jameco.com/z/GB218-Jameco
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