variable-speed belt grinder. Apparently, disused fitness devices make an ideal framework to build your own tools: Strong metal frames, plentiful adjustment guides, and strong treadmill motors.

the GoPlus 3-In-1 Treadmill goes up to 7.5 miles per hour for fast-paced runs during breaks or after work. And, don’t worry about slipping—it has a seven-layered, textured anti-slip belt.