Even something that seems as simple as "sous vide" cooking, which is basically a heater hooked to a thermocouple, took a lot of little innovations to make practical to hand to the masses.
And then, there's the general improvement in motors speed, precision, and cost, along with any number of advancements here and there and everywhere to make it practical.
Could someone thrust back to the 1970s and given a fairly substantial budget make some kind of 3D printer? Probably. But it's slow, extremely expensive, and can print various sizes of plastic bricks and spheres and other very algorithmically simple objects, and in rather low quality without many, many years further development. I can think of many ways of bodging on various improvements, but they're all going to have their own compromises, not be garden paths to what we now think of as modern 3D printing. (For example, someone could bodge together a machine that offsets a rod on the printer head, and then in the offset space, has an object to be "copied", by basically banging into the object with a very crude sensor, so there's no generation of geometry at all. But this is going to be clumsy, inaccurate, and full of very complex and disheartening limitations.) You're not going to be printing Dwayne "The Rock" Johnson's face embedded into a toilet [1] or anything, at 1MB of geometry. It will be commercially useless and inaccessible to hobbyists.
For me this is how meaningful technological progress happens. It is not like someone one day wakes up and suddenly has rocket that reached space caught back on landing by mechanical arms.
"Just adding a fan" is actually an extremely meaningful tech development.
Temperature control is probably hardest part. But in general air fryer could have been done quite a lot of earlier. Maybe materials for the basket is other aspect.
3D printing is not one of them.
People have been doing CAD/CAM since the 01950s. Boeing started using CNC in 01958 on IBM 704s, and MIT's Servomechanisms Lab (working with the Aircraft Industries Association: https://web.archive.org/web/20090226211027/http://ied.unipr....) sent out CNC ashtrays to newspaper reporters in 01959: https://en.wikipedia.org/wiki/History_of_numerical_control#C.... Pierre Bézier started writing UNISURF in 01968 at Renault, who was using it to design car bodies by 01975. The Utah Teapot was created in 01975, and it consists of nine Bézier patches; you could print the whole dataset on a business card: https://web.archive.org/web/20141120132346/http://www.sjbake...
The IBM 704 was a vacuum-tube machine that could carry out 12000 floating-point additions per second and had a failure about once every 8 hours https://en.wikipedia.org/wiki/IBM_704. The Intel 8008 (not 8088, not 8080, 8008) that came out in 01972 could carry out over 79000 8-bit integer additions per second, which is about the same speed. But much faster computers were already available, such as the PDP-8, in wide use for real-time control, and they very rapidly became much cheaper. Any computation MIT's Servomechanisms Lab could do in the 50s was doable by hobbyists by the 80s.
The reason 3-D printers mostly use stepper motors is that they don't require closed-loop feedback control. 2-D printers from the 01970s used stepper motors for the same reason. They were accessible to hobbyists; in the 80s I had a Heathkit printer someone had built from a kit in the 70s.
If you wanted to print Frank Sinatra's face on a toilet, I think you'd probably want at least a 64×64 heightfield to get a recognizable Sinatra; 256×256 would be better than the line-printer pictures we were doing. 8 bits per heightfield point would be 65 kilobytes, which would fit on the floppy disks we were using at the time. This would have been totally feasible, though digitizing Frank Sinatra would have been a nontrivial project, quite aside from printing him.
So I don't think computation was the limiting factor.
Your "basically banging into the object with a very crude sensor, so there's no generation of geometry at all" is called a "pantograph" and it has been a common way to copy three-dimensional objects and engrave letters with a milling machine for 180 years: https://en.wikipedia.org/wiki/Pantograph#Sculpture_and_minti...
I don't think that's a show stopper though. If we had had 3D printers in the 1970's and 1980's, sold at Sears, between the computers and the tools, you'd bring home a paper catalog from the 3d model company, thumb through it for models you wanted to build, send off a cheque (and a SASE) and they'd mail you back a cartridge that you plug into your printer so you can print that model. And then get that catalog in the mail forever after.
As reference on how much home computing power was available back then, the original Apple I came out in 1976 with a "character generator" and was not capable of advanced graphics - the cost of the amount of ram it would take to draw an entire screen from ram would have been astronomical, so characters were stored in ram and the card was in charge of outputting the characters and rudimentary graphics.
Models where severe limited, at most few thousands triangles per scene, but it was enough for talents to make crazy things.
Not exact. First, funny note, Seymour Cray admit, he used Macintosh to design Cray.
Second, existed activity of using Atari ST for 3D design, as sort of companion machine for special model of Commodore, which could process analog video. As I seen, they directly write frame-by-frame on Betacam.
Sure, rendering on ST with 68k was slow even with TV resolution, but they made lot of commercials on TV.
In late 90s, TV commercials made on MMX or Pentium-Pro with 16..32mb of RAM, and use PC frame grabber cards and RAID HDD. And that's history, how SGI become bankrupt - just when Maya was ported to x86 this become end.
https://futurism.com/expiring-patents-set-to-improve-3d-worl...
Other corps will just use your invention and just skip the markets where you have a patent. And yet their product will find its way there organically.
Many individual inventors that got patents openly talk about how useless and expensive they are.