A PVC pipe cutter is the quiet hero of weekend makers. With a squeeze and a click, it turns stiff plumbing leftovers into ribs for a palm-sized greenhouse that fits on a balcony railing. Start by slicing four eight-inch lengths for the uprights, then nick off two shorter pieces to form a peaked roof. The cutter’s razor wheel leaves glass-smooth ends, so there are no burrs to snag clear...