Today’s high-speed DVD drives have less than 40 nanoseconds to heat a bit position on a disk to its phase-change temperature, so anything that stays in the laser’s focus longer had better watch out—or prepare to be burned.
Thus was born the cheap diode-laser cutter and engraver: Get yourself an x-y carriage, a couple of stepper motors, a laser driver circuit, and a controller, and presto! You have an almost powerless, albeit very slow, cousin to the big laser cutters that have revolutionized small-scale flat-pack design and manufacturing.
But wait, there’s more—or rather less. A DVD drive already has a perfectly usable small stepper motor built in, along with guide rods that provide very precise single-axis travel. Mount two of them at right angles and you have the guts of a laser engraver that could fit in a very large pocket.
So I fired up my browser, read a real hacker’s description of how to do this at Instructables, and headed out to build my own, only to find that technology advances in sometimes inconvenient ways. First, I went to the local used-computer store, the one that used to have stacks of dead machines on pallets out back. No drives. Ever since e-waste recycling became the rule, none of the old hardware stays more than a month. I could call back and see when they got a burner-equipped machine in for scrap, but no guarantees.
With the fastest-rated burners going for US $22 each online, this was no great burden. But when my order came in, I found that the drives had a designed-for-manufacture mash-up of diode, heat sink, and circuit board instead of the easily removable diode module of years past.
After breaking the first diode I pried out, I decided to reuse the next one in place, including most of the optics. For best cutting it would have been nice to keep the close-focus secondary lens, but it was a Rube Goldberg marvel suspended by springs and magnets, with fine-positioning coils and a servo loop closed by image processing—in short, something I’m not up to hacking. So I finally left the primary lens in place and hot-glued another primary (pried out of the other axis carriage) on top of it.
I also went with a commercial laser driver circuit from AixiZ and a couple of cheap stepper drivers from SparkFun. Sure, the same circuitry might be available somewhere on the drives’ circuit boards, but finding it and convincing it to work for me instead of against me seemed like too much trouble.
With this cobbled-together bunch of hardware, building the software to burn images would seem to be fraught with trouble. It’s not. More than 30 years ago, engineers in the computer numerical control (CNC) machining business standardized something called G-code—essentially a virtual-machine assembly language for numerically controlled tools. And what’s a laser engraver but a numerically controlled milling machine with no z-axis and a very fine bit?
G-code is the lingua franca of the do-it-yourself CNC community, so of course a small cluster of hackers—in Norway, as it happens—has written a customizable G-code interpreter, called Grbl, that runs on an Arduino microcontroller. Tell it how far one pulse of your steppers should move your tool head, how fast to pulse the steppers, which pins everything is attached to, and a few other parameters and it does the rest. With free G-code generator extensions to various drawing programs, sending a page to an engraver is only slightly more complex than sending it to a regular laser printer.
It’s a little bit frightening just how straightforward it is to get all these disparate pieces to work together—and to think of the power lying untapped in discarded computer parts. I can hardly wait till Blu-ray drives (up to a watt of easily absorbed short-wavelength light) start coming up surplus.
This article originally appeared in print as "Laser Cuts Paper."