A read-out of chuck speed on variable-speed drill presses and lathes can be very useful. That particularly applies if you use an electronic speed controller but even if you have to swap gears or pulleys, it’s still good to have a display showing the tool’s rotational speed.

It's easy and cheap to make a tachometer that measures the rotational speed of your drill press or lathe. The project uses just a few low-cost components and a re-scaled tachometer from a car.

In fact, wouldn’t it be good if you could have a big dial displaying revs per minute? Hmm, cars have one of those – it’s called a "tachometer". And all modern tachos are driven by a simple pulse input, so it’s quite easy to adapt one to do the job.

The components

To make this speed display you’ll need to scrounge a tacho from a car. When sourcing many secondhand parts, you don’t want to go along to a wrecking yard and ask for the tacho from a specific model – not unless you want to pay top dollar, anyway. No, what you want is an orphan that’s going cheap or perhaps it’s part of a dash display that’s been discarded because the faceplate is scratched.

The Australian-built Nissan tacho used to make this display was sourced from the shop at the local tip. In fact, I got the whole instrument panel for just a few dollars. My guess is that it is from a mid-80s Australian-built Nissan Skyline or Pintara but that doesn’t really matter.

In addition to the tachometer, you’ll also need a 12V DC plugpack, a reed switch (eg, from the speedo of the same instrument panel), a small magnet, a 10kΩ trimpot, a 33kΩ resistor, a 1000μF capacitor and a box to mount it all in. To make a new scale, you’ll need a PC, scanner and printer.

By the way, many older Nissans use reed switches to transmit road speed from the mechanically driven speedo to the ECU. However, if you don’t get a reed switch with the speedo, it can be picked up quite cheaply from electronics stores.