Design And Build Your Own Circular Slide Rule

front view of a purple acrylic slide rule with white ink scale markings.

You have to really like slide rules to build your own, including the necessary artwork. Apparently [Dylan Thinnes] is a big fan, based on this project he began working on a few months back. The result is a set of algorithms that automatically generates most of the scales that were common on slide rules back in the day. For example:

K       Cubic scale, x^3
A,B     Squared scale, x^2
C,D     Basic scale, x
CI,DI   Inverted scale, 1/x
CF,DF   Folded scale, x*pi
LLn     Log-log scales, e^a*x
LL0n    Log-log scales, e^-a*x
L       Log scale, log10(x), linear
S       Sine and cosines scale, sin(x)
T       Tangent scale, tan(x)

If you’ve ever tried to manually draw an axis using a computer program — attempting to automatically set reasonable tick marks, grids, and labels — you can appreciate that this is a non-trivial problem. [Dylan] tackled things from the bottom up, developing several utility functions that work in concert to iteratively build up each scale. One advantage of this approach, he says, is that you can quite easily build almost any scale you want. We’re going to take his word on that, because the project is not easily accessible to the average programmer. As [Dylan] notes:

At the moment it’s still a library w/ no documentation, and written in a relatively obscure language called Haskell, so it’s really only for the particularly determined.

The project is published on his GitHub repository, and sample scales and demo program are available. Without knowledge of obscure languages and being only mildly determined, one can at least generate some sample scales — just downloading the Haskell environment, a few dependencies, and clone [Dylan]’s repository. The output is an SVG file which can be scaled to any desired size. In this follow-up Reddit post he discusses the fabrication techniques used for the acrylic circular slide rule shown in the lead photo.

It’s always been possible to make your own slide rules using pre-generated artwork — for example, the Slide Rule Museum website has a slew of various scales available in graphic format. But if you want to make a custom scale, or make one of that’s meters long, check out [Dylan]’s project and give it a whirl. For another take on making slide rules, check out this project that we covered last year.

9 thoughts on “Design And Build Your Own Circular Slide Rule

    1. A slide rule allows many different calculations to be made, one step at a time. A nomogram makes multiple calculations all at once, solving a complete equation, but that equation cannot be altered aside from a few input variables. So they’re really not the same thing at all.

      Nomograms can be made in the form of a slide rule and many for sale on the Internet are called slide rules, but are actually nomograms, capable of solving only a few fixed problems.

      For example, these are not slide rules, but nomograms calculating a fixed formula:

      1. I still probably have a couple of those. And yes, they were probably freebies from specific companies.

        Didn’t Radio Shack have a “slide rule” for resistor color codes?

        The ARRL had a circular Ligntning Calculator for radio related work. Not a freebie.

  1. I’m going to disagree that drawing tick marks, grids and labels is a non-trivial problem. Doing this, whether linear, cartesian or polar is not difficult at all in OpenSCAD, from which the results can be exported as SVG if desired.

  2. I have an ARRL Lightning calculator. It’s capable of converting wavelength to frequency, finding the resonance of a capacitor-inductor pair, and estimating the inductance of a coil based on diameter, wire length, and turns per inch. Still perfectly usable, but why wouldn’t it be? It’s not like the laws of physics have changed, LOL.

    I don’t know exactly how old it is but it says “Copyright 1932 W.P. Koechel” and was sold new for a dollar.

    Somewhere I have a book that briefly details the history of nomograms and explains how to design your own, from putting your formula in the correct format, to drawing the actual chart using the standard drafting tools of the day. At least I hope I still have it. Things tend to “walk off’ around here if you don’t keep close track of them.

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