Circular Slide Rule Made With a Laser Cutter




  • I ended up making this slide rule by accident. Was looking for log circular scales and knew slide rules have log scales. But the mass of numbers in the templates looked so pretty I decided to make a circular slide rule.
  • The pages on provide quite a few templates for different kind of slide rules. I used the scales for circular slide rules created by Savard. I decided to use the third Savard scale (link) as that one contains conventional log-log and inverse log-log scales. And the last Savardscale which would be the transparent overlay that would rotate on the opaque bottom scale. Big thanks to John J.G. Savard for these scales.
  • The video summarizes the construction process.

Step 1: Converting the PDFs to Laser Cuttable Files.

I imported the PDFs into Xara as a vector file and drew a red circle centered around the templates that would be recognized as a cut line by the laser cutter. The line markings were converted to a blue color and these would be etched as lines. The line widths were changed to 0.001 pt and the files were exported as high resolution PDFs. The numbers and texts were kept black and would be etched as raster images. The laser cutter compatible PDFs are attached here.

The transparent template was reversed to prevent parallax effects when the transparent plate was placed on the opaque base. I had scraps of thin white opaque acrylic and transparent acrylic with their protective film, so used these in the Epilog laser cutter.

This is a large slide rule, about 8 inches in diameter, unfortunately the transparent acrylic was just a bit small in one direction and you can see a tiny piece missing. Fortunately, the numbers and markings did not overlap the missing plastic bit.

Step 2: Filling in the Markings With Paint

Once the pieces were etched and cut by the laser cutter I removed the protective film. The film had melted into some of the markings requiring careful scraping off with a needle. Might have been better to etch without the protective film.

The pieces were washed with Dawn dishwashing detergent, dried and then black acrylic poster paint slurry was rubbed into the etched lines and letters. The lines took up the color quite well but the letters were not etched deep enough so appeared lighter in color. I should have turned up the intensity on the raster etching on the Epilog laser cutter.

Once the paint was dried I rubbed off the excess paint with a paper tissue moistened with 70% rubbing alcohol. A light coat of acrylic varnish was applied to seal in the paint.

Step 3: Assembling the Slide Rule

A 4mm nut and bolt were used to assemble the opaque base plate, the transparent top plate and a cursor. The back side of the slide rule is blank.

Now to practice my skills at slide rule calculations!

Step 4: Adding an Extremely Useful Metric Conversion Scale to the Back

I generated a metric conversion scale by using excel and then plotting angles with a drawing program, Xara.

The scale has length conversions; inches to cm, feet to meters, miles to km.

Liquid volumes; ounces to mL, gallons to liters, pints to milliliters.

Weight conversions; grain to mg, ounces to gram, pounds to kg.

Energy conversions; horsepower to kilowatts and calories to Joules. An of course,

Centigrade to fahrenheit.

Conversions can be done from or to metric.

I have attached PDF version of the conversion scale with the first version not containing any raster images (text and numbers) in black but instead the text and numbers are outlines by etched lines. The second version does contain text and numbers in black but still retains the outlines in blue.

Step 5:



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    Tip 25 days ago

    Designed new conversions scales for weight, volume, linear dimensions etc that can be printed on to the back of the circular slide rule. Uploaded two versions of PDF file for these. They are scaled for 8 inches diameter circle.