Thanks for the great comments guys, I feel like some good idea will come out of it.
I just got into the habit of cooling everything from being in crypto mining for years. The reality is that some GPUs are stable at 85 c for long periods, all of my properly-designed 5 year old GPUs are still running fine. I'm guessing that's much higher than what the PLA ever reaches under normal conditions, but I should find a way to measure that.
I'm absolutely certain my Zx-1881 does NOT need a fan at all but I added one because going overboard was part of the design idea.
Not only is the case really big (It was meant to fit a Zeddynet with the akward-pointing cable and a cherry-keys keyboard) but I designed it to have a chimney effect for passive cooling.
(warning: unflattering pics as requested, you can see what I mean when I say it's not finished
)
Front slot, cold air goes in:
Rear slot, hot air & cables go out:
I tested with incense sticks and get nice airflow passively when the PLA/CPU heat up. When I turn the fan on my own lap gets cooled, so it's really overkill.
But for my next Zeddy, I definitely want to treat the case with more reverence (it reminds me too much of the Monolith bringing the spark of intelligence
). Replacing the 7805 is mandatory but the heat sink could be reused to shape a passive cooling air path with almost-invisible external changes and ensure the machine works for another 40 years.
Well, without actual numbers I'm just shooting the breeze (eheh).