I’ve heard of bootstrapping a machine shop from a lathe as well—apparently there’s a series about it, written by this guy: https://en.wikipedia.org/wiki/David_J._Gingery
It is information like this that makes you realize how incredibly fragile our civilization's tech stack is. Most of our physical tech stack is read-only executable code: there isn't a civilizational "source code" that shows from first principles how to build up to our current technology layer. For that matter, not even from first principles to turn of the 20th century technology level. We take a most of our tech stack for granted. This would matter if we had a civilization-wide energy crash, so if the catastrophic-scale climate change or oil crash predictions come true then this would be more than a passing interest for just the recreational primitive tech hobbyists.
With a fertility rate of 1.3 among the intelligent (read: technologically capable) peoples of the world, we are far more likely to run out of people to maintain the technology than we are to run out of the energy to power it.
Indeed, if you walk into any utility company or similar, who do you see doing all the work? Middle-aged-to-old working-class white men. What happens when those men retire? Who is going to hold the infrastructure together?
Unlike a civilization-wide energy crash, this is not merely a rhetorical question.
Are you using the number of 1.3 from people with university education in the rich world? It seems a very narrow window through which to view humanity'a 'capable' people, who exist in all shapes and forms, all colours, on all continents, and often arise from deep poverty without any formal education, my grandfather for instance
IQ is substantially heritable. A child's IQ is (more or less) the average of his four grandparents. The IQ of his four grandparents is largely the result of cognitive assortment within a breeding population with a certain mean IQ.
If a population's mean IQ is 70, the percentage of people with an IQ above 130 is 0 (out to four decimal places).
If 85, 0.1%.
If 100, 2.2%.
If 115, 15.9%.
The mean IQ of the white race is about 100. The mean IQ of SS Africans is about 70. The mean IQ of Arabs is about 85. The mean IQ of Chinese is 105 or so. The mean IQ of Ashkenazi Jews is 110-115, depending on how you measure it (they are a special case).
There are probably more people possessing IQs of 130 or above in Israel than in all of Africa.
The number 1.3 comes from a rough average of the fertility of the white nations and of the high-end Asian countries, namely Japan, Singapore, Hong Kong, and to a somewhat lesser extent mainland China.
Unfortunately during a collapse of society you very rarely find hospitable environments. By the time society itself recovers and has the resources to spare everyone who knew of the old world is dead and a lot of the artifacts are ruined or destroyed.
Seed vaults, storing equipment and books in salt mines, etc should prove extremely helpful if such a dire situation arises. It might take a lot longer to rebuild though because there won't be any cheap, easy oil to burn.
The winning strategy so far seems to be duplication, so it's about time we get some colonies on other planets to help ensure continuation of the metaspecies.