Calculator Keypads: Laser Cutter

My last post on building calculator keypads explained all the methods I tried then presented on at the 2023 Hewlett-Packard Handheld Conference. Last year, I bought an Elegoo Phecda Laser Cutter as the next step in building keypads, and the results are really impressive! This particular model uses a laser diode which is much cheaper than other types of lasers like CO2. Common power ratings for diode lasers are 5.5W and 10W although some as low as 1W are used for etching rather than cutting. My laser cutter is a 10W model and also comes in a 20W version that is a lot more expensive. As it turns out, 10W is more than powerful enough for building keypads. Diode lasers like this one have a couple limitations - they don't cut blue material well since it absorbs the laser wavelength and they can't mark or cut harder materials like metal. They also aren't supposed to be able to cut white acrylic but mine punched straight through 3mm of black acrylic and 3mm of white acrylic underneath it.

The first thing to figure out was the software to run the laser. A lot of people swear by LightBurn which is $99 for the license plus an extra yearly fee to access updates. Instead of that, I went with LaserGRBL which is free and works on Windows. Since then, I switched my laptop over to Ubuntu, so LaserGRBL needs to run in a virtual machine. My laser cutter was shipped to my next work destination, so I'll need to wait a few months to test that everything works. Setting up LaserGRBL was really easy. It includes test images for cutting to figure out the ideal number of passes and laser strength to use on a particular piece. For etching images, the default resolution was pretty low, so I changed it to 16 lines per millimeter since the focal size of the laser is 0.06 x 0.06mm. This was enough to get it cutting and etching exactly how I wanted. Generating images for etching was easy using Python to create an SVG then converting to PNG as with my other keypads. The laser's cutting mode uses SVG images directly.

The most useful material for keypads that the laser can cut is acrylic. Several companies sell sheets of it in various thicknesses such as 3mm and 1.5mm. What finally convinced me to buy the laser was two-tone acrylic which has a base layer of one color with a very thin layer of acrylic of a different color bonded on top. Lasering off the top layer exposes the color underneath which can produce very crisp details for lettering. Text down to 2mm is legible which is more than good enough for keypads. Another thing I experimented with was lasering letters into single-color acrylic and filling the letters with paint. The cheap acrylic paint I got from the craft store didn't work well for this, but it may work with better paint.

Another interesting option is custom, UV-printed acrylic where a full color image is printed on the acrylic. Custom Made Better (CMB) sells 12x18 inch custom pieces for $25. A piece this big can really fit a lot of keypads on it if it only contains the key faces and the underlying grid is 3D printed. The image is printed at about 300 DPI according to the website, so I emailed them to ask if it was 300 DPI exactly. Creating a grid to cut the keys out on the laser is trivial if the DPI is correct but even a small error in the DPI means the cuts will be misaligned by the time the laser gets to the far edge of the keypad. Since CMB couldn't guarantee the print would come out at exactly 300 DPI, I added several copies of the keypad design at slightly different sizes hoping one of them would account for any variation. In the end, the image was printed at exactly 300 DPI and came out looking better than any of my other keypads. It's not clear yet if the UV-printed ink will stand up to a lot of key presses, so more testing is needed.

UV-printed acrylic, two-tone acrylic, smallest keypad size for protoboard