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Comment by klyrs | Hacker News Reader

A block of metal is great heatsink, and a long ruler like that is both thermally conductive and has decent surface area to radiate heat away. More importantly, a fan is not a carpentry tool. Now, one could use a drill, shop vac, or circular saw to generate wind, but they'd be much less energy efficient than the passive radiator.

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For long term applications I much prefer passive cooling (AKA a hunk of metal.) I have one Raspberry Pi 4B in a case with a small heat sink on the processor and a small fan driven from the GPIO pins. It keeps the processor within limits even when overclocked and heavily loaded. Some day the fan will stop working and the processor will overheat (under heavy load) and throttle to prevent self destruction.

I have two Compute Modules (CM4s) and found a passive heat sink that is finned aluminum that covers the entire module. There is no fan to fail. I can overclock the CM4 to 2 GHz and load it for stress testing and it remains well within limits. One of these is equipped with an NVME SSD and I was surprised to see it reach excessive temperatures under heavy loads despite the PCIe x1 connection on the Pi. I got a "hunk of copper" NVME cooler, cut it to fit a 2230 NVME and it keeps the NVME SSD within reasonable limits.

Doesn't that really depend on the metal? E.g. copper is a great thermal conductor while stainless steel a really poor one.

Combination square blades are normally plain carbon steel, not stainless.

Actually, almost nothing in a wood shop is stainless because it sharpens poorly[0] compared to O1, A2, or any of the other tool steels you'll find in a wood shop.

[0] Yes, I realize that stainless and carbon steel are two whole classes of alloys, all with different characteristics. Based on my experiences with kitchen knives, I'll stand by my claim that at least the common ones sharpen poorly compared to the common carbon steel alloys.

Of course it depends on the metal! But for a hackjob like this, I'm betting it was run without any thermal management first, and then with the ruler as the first thing at hand... that the effort succeeded at that stage suggests that the alloy is sufficient.

I didn't understand the blog post as a challenge to only use carpentry tools but think he used what was available in his shop. (Most carpenter wouldn't have thermal adhesive tape or a thermal camera either ;-)

Circular saws sure do produce a surprising amount of wind, but the thought of using one for cooling is horribly terrifying.

Thank you

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