CDs (Compact Discs) and DVDs (Digital Versatile Discs) are not analog storage mediums, but CD and DVD drives are mechanical devices. Both types of disc store data bits on their reflective surface. A laser is shined onto the surface, and if it is reflected then that signifies a 1 bit; if the laser beam is not reflected, then the bit is a 0. The disc is spun at a precise speed by a DC motor, while a stepper motor is used to move the laser across the disc. Because you can probably find used CD and DVD drives in the dumpster behind your local thrift store, you can use their stepper motors to build an affordable and simple laser engraver.
To be clear, the laser inside of a CD or DVD drive isn’t powerful enough to actually do any practical engraving. Blu-ray burner drive lasers should be strong enough, but it’s probably easiest just to buy a new laser module. You can find these in the 500-2500 milliwatt range for less than $50, and those should be strong enough to engrave card stock, cardboard, and even wood if you move the laser slowly. Don’t worry about the size of the laser module, as it will remain stationary and the work piece will be moved in the X and Y axes by the upcycled stepper motors.
To tackle this project, you’ll start by disassembling two optical drives. It doesn’t matter if they’re CD or DVD drives, but it helps if they match. You’ll keep the frames, the two rails, the carriage that rides on them, and the stepper motor and lead screw to move the carriage. The two stepper motors — one from each drive — will be controlled by an Arduino Uno through a CNC shield using GRBL firmware. Those CNC shields are available from a variety of sources for as little as $10. You’ll place one drive on top of the other, with the rails perpendicular to each other. This will let you move your work piece in both horizontal axes. Inkscape is free software with plugins available to translate your designs into G-code commands that the GRBL firmware will understand. If you want a very affordable laser engraver, this is a great DIY option.