A couple of years ago, my old shop vac failed. That article describes how I found the fusible link that was protecting the motor was nothing more than a piece of solder. It had heated enough to get soft and open the power connection, keeping the motor from running. I was appalled. Nevertheless, I put a piece of solder in it and the vacuum worked - for few weeks until that piece of solder softened. I eventually tossed out the thing and bought a battery powered Ryobi for cleanups around the shop, the house and when washing the cars.
When I tossed out the old Shop Vac brand, I kept the 2" hoses and all the accessories but the Ryobi uses a different sized hose so everything sat in a few corners.
The Ryobi actually worked OK, but about a year ago, I got tired of it not being working every time I needed it and bought a different brand, higher power shop vacuum; a Ridgid. Now I could leave the vacuum in a corner and if I can hook up the old and new 2" hoses I can reach the entire metal shop. Except the hoses don't mate. Both ends of both hoses are the same smaller diameter (about 2-1/4") that plug into a bigger hose fixture in either an extension wand or the vacuum body or the fixtures designed to go on the hoses.
As an RF engineer (working at Radio Frequencies), this is second nature. We always would need multiple cables (colloquially called hoses) to get across a few benches and need to connect things that wouldn't connect. There is literally an entire industry of making and selling adapters between things we might try to connect and a set of laws that reflect on what we see. ("Given a need for N adapters, the engineer will never find more than N-1", and so on). I knew what I needed, I needed a plastic adapter big enough to plug both ends into. Nothing more than a plastic pipe that had to be a specific size.
This sounds like it should be doable on my 3D printer. It doesn't take long to design a pipe. Make a cylinder of the right length, right inner and outer diameters and you're there. A couple of days ago, I made a test piece just to make sure a couple of inches of what will eventually be four inches long would fit the hoses. It fit just fine.
I was about to print a full-sized version, when something hit me. The Ridgid hoses have a feature I've never seen before: the mating sections to the hoses have triangular, saw tooth-like pin on a flexible lever. It mates with a section on the fixtures or the vacuum cleaner itself and acts as mechanical insurance. I decided to create a model of that and add it to the full sized adapter. It took a couple of hours to draw that (essentially point by point), turn it into a solid model and set it up to print. The whole adapter took six hours to print, but here it is coming off the printer.
And here it is doing its intended job - joining the old Shop Vac hose (right) and the Ridgid hose (left).
Here's a closer view of the Ridgid locking tab. This doesn't look quite right, so I'll have to look at it a bit more closely. Perhaps the mating teeth on the adapter are a bit too close to each other. Or maybe it's just slightly out of position.
As you might expect, I didn't declare it done without vacuuming up around the shop and pulling the cleaner by the hose. No problems.
I'm not sure the adapter I needed doesn't exist anywhere, but I had looked around a bit without finding them. In terms of just the plastic for the print, this cost about 45 or 50 cents. There is no compensation for CAD time or anything else. I'm not saying it makes sense to buy $300 or $325 worth of printer, filaments, dry boxes, and everything else to print an adapter. I'm just saying if the printer is in your shop, the problem is solved.