We have an IKEA Beddinge sofa-bed that lives in the basement room of our house. It's useful if we want to sit and watch films on the large screen I use at my desk, or to use as an extra bed for guests. Less is useful that, to do these things, it has to sit across the room, exactly opposite the door and gets in the way. To stop it being so stubborn we added wheels.
IKEA doesn't make the Beddinge model any more, but there are plenty available second-hand. I suspect they still live happily in a lot of homes, and adding wheels can make them much more flexible.
The base of the Beddinge is a simple frame with four metal tubes, ~57mm internal diameter, that act as the feet. Usually these 'tube feet' have a plastic cap on the bottom to spread the weight, and on top to keep dust out.
Given this design I almost assumed IKEA might sell some wheeled inserts that you could slip in to make the sofa mobile, but they don't; nor has anyone come up with a commercial solution. The closest I could find is a model on Thingverse.com to 3D print the kind of insert I imagined, but I don't have a 3D printer.
Making something out of metal is hard, if you don't have a workshop with right kind of equipment, and I have as many metal working workshops as I have 3D printers. I have equally many wood working workshops, but luckily my brother does have access to a wood workshop, and more importantly the skills to use it, so he did, and built these rather nice hard wood inserts for the feet.
The design is pretty simple. A (mostly) round upper section, securely connected to a flat base that is large enough for whichever caster wheels you buy, and have enough room that you can drill four holes for the mounting bolts.
While the design is simple, if you make your own, there are some things to make sure you've considered.
First is weight. There's no weight limit for the sofa given in the manual, but it was sold as a three person sofa, so if we assume something like 90kg per person (on average), plus the approximate weight of the sofa itself, of 30kg, we have a total weight of 300kg to support. When buying your casters make sure they specify their load bearing capacity. I bought some Dörner & Helmer Apparate-Doppelrolle 50mm casters from a local hardware shop, which say they can carry up to 80 kg each, making a total of 320 kg, which is above the weight we estimated, and hopefully be enough. I also found the smaller wheel size of these 50mm casters nice, as otherwise the sofa is suddenly much higher up, which is less comfortable for smaller people.
When making the inserts, it's important to make sure the square base and the round insert are very securely connected, e.g. it's going to need more than glue. As the caster wheels have a slight off-set, there is a bending moment that will try and tear the base from the insert. Bolting the two together is one option, or perhaps even making it our of one piece of wood. In my case the round insert actually has a tab that extends and (as is just about visible from the different colours of wood in the picture above) fits into the square base, giving a nice positive fit.
The other weight consideration is the surface on which your sofa is standing. Before the weight was spread across four flat feet, now that same weight is concentrated on the smaller points of the wheels, so make sure your floor is suitable.
Before you set your sofa free and let it roam, you have to be able to stop it from getting away, especially if you want to sit on it. At least two of the caster wheels should have brakes on them, on opposite corners. I splashed out and bought all four with a brake (it did make them slightly more expensive, 9.45€ for braked, and 6.95€ without), but it means it won't go anywhere if I don't want it to, plus it's easier to get to at least two brakes even if it's stood against a wall.
Last, make sure the inserts are tight fit. The best approach is to make them slightly too big, and then sand them down. Adding material later is much harder. You should be able to push them in by hand, perhaps with a bit of twisting. Don't use a hammer or similar to force them in, this might cause the round foot to split, leaving you with broken sofa frame.
Now we can let the sofa roam free, or more importantly, politely turn it and push it up against the wall where it doesn't get in the way so much.