THe problem is that about 10-20% of a 3D printer is not printable with current technology. It is, to date, impossible to print a motor (because you cannot print a magnet). It’s also very hard to print a bearing, and even harder to print one that’s any good.
Then there’s the fact that a metal 3D printer tends to be a laser sintering a metal powder, and thus needs to be bigger than the thing it produces. Admittedly, with a bit of clever trickery you can avoid this (assembly after printing), but then you’ll lose accuracy.
Now, it is potentially possible if you are 3d printing iron and have some very clever things going on. You could make a weak magnet by magnetizing it yourself, and you’d have to combine it with a plastic 3D printer to produce the insulation on the windings - perhaps some sort of plastic dip would be better for that though. Then you make a whole bunch of parts, and with a robotic arm that exceeds current levels of dexterity, assemble your new printer.
Estimated Size: >1m
Estimated Mass: >30kg
Estimated Unit Cost: >$10,000
Estimated Development time: > 25 man years (ie 5 people take 5 years, 25 people take 25 years)
Estimated Development cost: > half a million
Estimated Power Draw when operating: > 500W
Now admittedly, we could think smaller. But then accuracy becomes hard and I suspect development time would increase, driving costs up even more.
Visual appearance: a box filled with metal powder, a robot arm on one size and a laser on an XY plotter across the top. A fancy actuator/brush that I can’t remember what it’s called to put on the next layer of metal powder.