NOTE: I'm really interested in making a Proper Reproduction composited from many scans, so if you have access to an original print, PLEASE contact me!

Back in the 30s, the Amateur Radio Relay League released a series of circular slide rules that allow for quick solving of commonly needed electrical engineering calculations called Lightning Calculators.

Right now, I only have some partial scans of Type B - the Ohm's Law version. It's pretty awesome - you can quickly find any two of resistance, voltage, current, and power if the other two are known.

This is just a hacky prototype that I made to work out the fabrication process (it's not a complete scan so no point in striving to make it perfect right now), so the cutouts are a little sloppy and hand-traced. Some of the power and microvolts scales are not reproduced in the original scan, and there is an image of the original wiper in the background as well. I literally just downloaded the images from Theodore Munk's blog and cut them apart in Photoshop. But it works!

The linked github includes the master Photoshop file as well as .pdf files and Silhouette Studio project files suitable for cutting on a Silhouette Cameo machine.

In addition to the cardstock for the graphical bits, you'll also need some thin transparent PETG to make the pointer and a 0.25" rivet for the center bearing.

Again, I'd really like to make a real reproduction of this, so if you have one let me know!

Known Issues

  • Parts of several scales on the baseplate are cut off in the original scan (low ohms and most of watts)
  • Some slight distortion on selector wheel. Values are still pretty close though.
  • Full size base might have something wrong with alignment marks - I have a hard time getting my Cameo to recognize it. it. Scissors work too :p