Acrylic circular slide rule with paint fill

Trying to reduce the sliding friction from my attempt in plywood, I applied the same design to black acrylic with paint fill in the etches and scores. I see a few spots I missed that I will need to touch up, but the technique works very well!

I painted over everything with a thin layer of white acrylic paint, let fully dry, then scrubbed off with a soft damp cloth. It’s almost like scratching off a lottery ticket.


Nice! The details on that really stand out with the white on black! :grinning:

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Instruments… so tasty. This pushes all my fiddly little buttons that love watches and whatnot. In fact, I wonder if anyone sells a watch with an easily lased face? Maybe a plain anodized face? scribble scribble scribble idea


Oh, I like that idea about the watch face. I’m definitely going to be on the lookout for one I can re-purpose now.

You are going to blow people away when they asked you where you bought it and you tell them, “Nowhere, I made it…”

Came out excellent.


Wow! That turned out awesome!

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The detail on that really is spectacular! What is the diameter?

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Really nice with the white on the black. Great job!

Love this!

4" for the inner disc.

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Love the engraved paint fill! Its my secret weapon for making something look manufactured.

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Looks great! How are the two discs fastened together?

It is a 3-ply sandwich construction, with a wider outer ring in the middle layer creating a tongue that slides in a groove formed similarly with the inner rings. I got the idea from this Instructable. Some modifications to try to reduce sliding friction: the middle ply doesn’t actually meet up (the groove is much deeper than the tongue sticks out), and since my design is single sided I didn’t bother gluing on the backside outer ring. If you don’t get it perfectly concentric, it introduces an opportunity for sticking. My design is registered only by the top face.

If anyone else is interested in slide rules, I now have two programs to generate scales and ticks in SVG.


This is awesome! I actually have to make a replacement part for some vintage equipment, it was this exact kind of setup, lines in acrylic filled with paint. I had hoped I could do it with the GF when it arrives, and this verifies it. Good stuff!

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Programs that you wrote? I’m interested!

I’m also interested!

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Me three.


Yep, I’m in. Awesome!

Okay, well, here’s what I’ve got. The first is the one that outputs my special purpose dosage calculator, the second is a more general purpose linear Mannheim style slide rule. They are written in Ruby, using the rasem library for SVG output (gem install rasem to get it).

Even for people who aren’t interested in slide rules, there may be something of interest to be found within on how to generate SVG programmatically from ruby.

Some random comments:

  • The circular rule generator is a special purpose rule that is unlikely to be interesting to anyone who isn’t a doctor. Well, it still works as a four decade logarithmic scale for multiplying and dividing numbers under 10,000, except the inner scale cuts off at 300.
  • If I’m generating two paired scales (A/B or C/D scales, where the ticks are identical and are opposed to each other), I try to generate the tick and labels as a single segment, to be bisected by the cut line later. This makes for better scores and reduces cut time.
  • The loop index is an integer that represents 1/10. This worked well except for in my circular rule where I wanted half ticks (.05) in the interval from 1 to 3, so there is some special casing there. You can see in the original photo where I screwed it up, there is a tick missing after the arrow around 2.2; that has been fixed.
  • As I mentioned, you can’t actually use the resulting SVG file to engrave without converting text to paths in Inkscape or Illustrator first.
  • For the circular slide rule, engrave and cut the top face along the red line, the bottom ply also on the red line, and the middle ply on the brown and green lines. They form two sandwiches: outer is red, brown, red; inner is red, green, red.
  • I haven’t figured out a satisfactory assembly for the linear rule. I have a 3D printed body now on which I will try applying an engraved veneer.