I wish I’d known!

a.k.a. F.M.M. Frequently Made Mistakes

a.k.a. The Virtual Wall of Learning


I thought I could run a(n) LED strip / relay / speaker / motor from an Arduino / Raspberry pi pin

Arduino pins can only supply 40 milliamps, absolute maximum, and 150 milliamps for the whole chip. It needs a transistor or even a more sophisticated driver chip to run those loads.


I used feeds and speeds designed for flood coolant and high-end endmills with cheap, used endmills, cutting dry

Oops. This can lead to broken tooling. Check charts in the shop or discount published speeds by 50%.

The CNC router didn’t sound good, so I reduced the feed rate. I still didn’t like it, so I reduced it some more.

Reducing the feed rate too far will make the chipload too small, making the bit rub rather than cut, and reducing the ability of the chips to carry away heat. Worst case, this will melt aluminum and set wood on fire.

3D Printing

I 3D printed a box.

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