When high-tech companies go belly-up, much of their equipment ends up on the surplus market for pennies on the dollar. I took advantage of this to cobble together a computer-numerically-controlled (CNC) router table so that I could cut complicated shapes in wood, plastic, or sheet metal without the usual hassle of making paper templates, trying to follow them by hand, filing down the rough spots, and, often enough, messing things up completely.
This is not your father’s router table, the kind you might buy at your local Home Depot. Those are merely stout tables designed so that a router can be mounted underneath with the business end sticking up. They’re great for shaping the edge of a straight piece of wood, but not much else. A typical CNC table, by contrast, puts the router above, with its bit pointed down and moving under computer control along the x , y , and z axes. While an off-the-shelf CNC router table could set you back anywhere between a few thousand and a few tens of thousands of dollars, the parts for mine cost only about US $1000.
The basic mechanical building blocks for this project are linear actuators—motorized devices for moving things in a straight line with great precision. Some CNC hobbyists build their own actuators (which are also called motion stages), using such commonplace items as threaded rod, metal pipe, and roller-skate bearings. While I applaud their pluck and ingenuity, I’m leery about such contraptions.
I chose the surer path, buying five industrial-quality motion stages on eBay for about $500 in all. This was a steal. Given the current economic malaise, I would expect more bargains to become available regularly. The largest actuator, roughly a meter long, was once used on a machine that tested integrated circuits, or so the sticker on the side suggests. It now serves as the gantry of my CNC setup, which is carried back and forth over a distance of about 60 centimeters by a pair of matching Japanese motion stages. The other two actuators are also identical and quite small, with a throw of less than 10 centimeters. One of them operates the z ¿Äëaxis of my table, with the help of parts from its mate, which I cannibalized to make the first one a little beefier.
After fabricating a few metal bits and pieces, I bolted the four stages together—the long one for x , two medium-size ones for y , and a small one for z [ see photographs].
To drive the actuators, the RollsRoyce solution would have been $100 servomotors and optical encoders, which would have provided feedback so that the computer couldn’t possibly lose track of the router. Instead, I used $15 secondhand stepper motors, which move my router around pretty briskly and with so much force I’m unable to stall its movements by hand.
Stepper motors need electronic controllers, which fortunately are widely available. For example, Xylotex offers a three-axis unit complete with stepper motors for $410. That package would take much of the pain out of building a CNC system, whether for a router table or, as is commonly done, for adding this capability to a small milling machine. Of course, you’ll have to take some care to hook up your motors and limit-detecting switching properly; you’ll also want to prevent the cabling from getting tangled. Check out the Web site of KabelSchlepp, a name that always makes me chuckle, for ideas.
My control box cost somewhat less than the Xylotex unit because it uses a home-brew motor-power supply and three industrial-surplus stepper controllers that I scored on eBay for $45 each. In hindsight, if I add up the time—and finger burns—involved in wiring everything together, it doesn’t seem like such a bargain.
To translate movement instructions on my computer into step and direction signals for the controllers, I use a program called Mach, from ArtSoft. The free demo version is limited to 500 lines of G-code, a low-level programming language commonly used to run machine tools; a Mach license costs $175. Or you can drive your CNC setup using EMC (Enhanced Machine Controller), originally developed by the National Institute of Standards and Technology and now available for free under a public license.
To mill complex parts or make fancy engravings, you’ll need computer-aided design (CAD) and computer-aided manufacturing (CAM) programs. Mach comes with a beta release of something called LazyCam, which I’ve not yet tried. And the Internet is overflowing with low- or no-cost CAD packages, many of which are listed at Freebyte.com.
With all the free or inexpensive resources to be found online, gearing up to do CNC machining at home won’t require you to tap your dwindling 401(k). But don’t let that lull you. As providers of the equipment and software caution, a computer-controlled machine, like any power tool, can be dangerously tricky.
So before spinning a sharp router bit or end mill under computer command, think about all the times your PC has done something unexpected. That should keep you in an appropriately cautious frame of mind when the chips start to fly.
Stepper motor: http://www.xylotex.com
Mach software: http://www.machsupport.com
CAD software: http://www.freebyte.com/cad/cad.htm
To Probe Further
For more on automating your home shop, see "Automate Your Home Shop" audio slideshow