In this video I show you how I build a classic, robust, super versatile T-slot linear slider out of cardboard. The big decisions happen right up front: the width and length of your sliding “tongue.” If you go wider, your top guides have more room to grab and you get a stronger hold-down. If you go longer, the whole mechanism gets more stable and durable—but you trade away some range of motion, because you’ll hit the ends sooner. From there I walk step-by-step through the side guides and top guides. I like making the side guides from the same thickness cardboard as the slider so everything sits flush without fussing over height, and I’ll even add paper as a low-friction liner (just don’t leave hot-glue globs). Then I do a little bit of simple “math” for the top guides so the handle can pass through the middle gap without getting covered. Finally, I tune the tension: if something rubs or binds, I’ll reheat hot glue with a heat gun (a hair dryer might work) and nudge the fit instead of shaving cardboard forever. Test constantly while you build—catching mistakes early is the whole game.