Pi Day inevitably involved tasty beverages, so I decided to make some Pi-themed coasters at TechShop to keep my table dry and safe.

To laser-cut the coasters, the first step is to pick a design. I knew I wanted mine to be in the shape of the letter π, but I also wanted it to have be solid and evenly support a cup, so I went on a font search. Eventually I found on Poplar Std Black, which seemed to have the properties I was looking for.

To design a coaster with inscribe text in Illustrator:

Make your artboard 4" x 4"; this seems to be the ideal size for a coaster
Using the Type Tool, draw a pi at the biggest font size available
Select the text box and choose Type > Create Outlines
Change to an outline by setting the fill to transparent, the stroke to black and the stroke width to .001
Release the outline: Object > Compound Path > Release
Duplicate the outline layer; since we will want to use different laser setting for the text and the outline, it will be easier to hide a layer at a time.
Find the text you want to inscribe (in my case the digits of pi), and copy them onto your clipboard
Using the Area Type Tool, select the outline path, and paste in your text (I used 8pt Times font for the digits)
Double-click Area Type Tool, and add 1/16" margin around edge
Finally, repeat the steps to turn the inscribed text into outlines:
Select the text box and choose Type > Create Outlines
Change to an outline by setting the fill to transparent, the stroke to black and the stroke width to .001

Note that it's certainly possible to raster letters with the laser, but I prefer the effect of vector cutting the outlines of the text.

Pi Coaster.ai
Download

Step 1: Cut and Finish the Coasters

Lasers! To make multiple coasters at once, I just expanded my artboard and copied the grouped layers.

I made my coasters from 1/4" Baltic Birch, so the laser settings here are what worked for me for that wood on an Epilog 60W laser.

First, etch the text: hide the outline layers, and set the laser to Speed 30, Power 5, Frequency 5000.
Next, cut the coasters: hide the text layers, and set the laser to Speed 14, Power 90, Frequency 500.

Finally (and optionally), add some felt to the bottom of the coasters to class them up. If I had been more clever and had the felt with me when I was lasering I would have cut it there, but it's simple enough to outline the coasters with marker and cut the felt with a scissors. Just glue the felt to the backs with some spray adhesive, and you're done!