Sewing machines
We have a Swiss-made Elna Carina Electronic SU which is advertised in Popular Mechanics October 1978 as having a pneumatic foot pedal and electronic control of the needle pressure.
Unusually, the lower bobbin is mounted horizontally behind the needle instead of vertically from the front.
There are two versions of the manual that you should refer to if you are doing anything. If you can't be bothered to read it, use the index page at the back "To remedy minor disorders" when it's not doing as you'd expect.
There are many embroidery features and a set of 2-axis dials for doing different patterns. There's a booklet of these plastic dials that independently control the advance and side-to-side motions. Someone with a lot of time could 3D print new ones, but there's probably a limit of about 12 stitches on it, so it would be more versatile to use servomotors to poke the two control levers -- or just buy a modern electronic sewing machine.
We have 2 overlockers, both Bernina Funlock (Impy is a 007D, Bernie has no model number). We keep Impy threaded with white thread, and Bernie with black thread, which means you can easily pick whichever machine works for you. You're obviously welcome to bring your own thread and rethread either or both, but it would be appreciated if you also rethreaded with the existing colour when you're finished. The idea is very much that either colour is ready to go whenever.
Important note: neither of these will run if the front case is open. This is a feature, not a fault.
Impy and Bernie are functionally the same machine and need to be threaded the same way as each other. To this end, either machine has a threading diagram inside the front cover (pull the right-hand side of the front cover out to the right and it will fold open).
Please note that the numbers at the top indicate which order the machines need to be threaded in.
If you're struggling based on the diagram, there is a youtube video here which shows the process on a slightly different machine. The instructions are still accurate for ours. You're always welcome to ask for help.
Overlockers cut the edge off your fabric whilst also sewing and wrapping the thread around the edge. This is great for stretchy fabrics as it means the seam can still stretch without having to faff with elasticated thread. It can also help to limit fraying in woven fabrics, and provide a nice finish.