The world of mechanical engineering is full of interesting and ingenious mechanisms. The Geneva drive, for example, translates rotary motion into intermittent ticking — perfect for a wristwatch or clock. With a clever mechanism, one can reduce the need for complicated control electronics. That was the case with the self-reversing screw that moves the guide on Mr Innovative’s automated winding machine.

This is a winding machine for loading string, thread, yarn, or wire onto a spool, similar to the bobbin winder that you would find on a sewing machine. To ensure an even and tight winding, the machine must guide the thread back and forth along the length of the spool. Many of us would jump right towards electronic control to guide the thread, maybe involving a stepper motor and limit switches. But as Mr Innovative shows, that isn’t necessary. All he needed was the right mechanism: a self-reversing screw.

Like most of the mechanical parts on this machine, the screw was 3D-printed. It has threads running in both directions, so it can move the guide in either direction. At the ends, there are grooves that cause the guide to flip over to the other threads so it changes direction. This simple mechanism is driven by a single geared DC motor.

A second DC motor turns the spool, so it winds the thread around itself. An Arduino Nano board controls both motors through Mr Innovative’s custom driver board. The sketch is very simple and simply tells the motors to spin at a set speed as long as it has power.

In addition to being useful, this machine illustrates the importance of well-considered mechanical design.