How To Build Your Own CNC Machine

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The drive screw is the next piece of our project. Commercial units use linear ball screws or linear gears. The commercial parts aren't cheap, but you can get away with some 1/4-inch threaded rod from the hardware store. Instead of antibacklash nuts, we'll use these handy 1-inch long 1/4-inch nuts. Just about every hardware store has them, and they produce very little play. Try out the hardware at the store because defects in the nut or rod will produce drag that's easily noticeable by spinning the nut on the rod.

To couple the rod to the motor shaft, we'll use vinyl tubing with a pair of collars. The tubing is 1/4-inch inner diameter and prevents binding by allowing some play between the rod and the motor. You can get suitable collars from a model airplane store (The hardware store had some, but they were overpriced). Alternatively, you can make your own like we did from nylon bushings and hex screws.

Finally, we'll need some linear slides. One easy out is to purchase a used or surplus XY table that's built just for this purpose. Custom designs can be built using ball bearings. Above is the linear rail that ShopBot uses. They machine the edge of a piece of steel and use this cool angled roller bearing.

We built this linear slide from a 1/2-inch steel rod and multiple bearing surfaces. It works, but we don't recommend building it if you value your sanity.

Once you've bought or salvaged a set of motors, you'll need a controller. The controller provides the interface to the computer, drives the motors and can provide some simple feedback to the computer. The stepper controller has to be powerful enough to drive the motors you've selected. We sifted through lots of stepper controller designs looking for one that presented the best value.

In the end we found this design for a relatively simple parallel port interface that originally appeared in a 1994 issue of Nuts and Volts. Today, the expensive UCN5804B is only available as a surplus item, but now the entire controller can be built for about $22-$30 in parts. (If you use a heavier motor like the ones from the Imagewriter, you might need to add some separate power transistors.)

The parts list at the link is a bit outdated, here's our updated shopping list. · · · · · · · · · · · · 3 - UCN5804B - alltronics.com 12 - 1N49355 Diodes - Part 625-1N4935 from Mouser.com 2 - .01uF Capacitors - Part 581-SR155C103KAT from Mouser.com 1 - 10uF Capacitor - Part 140-HTRL25V10-TB from Mouser.com 3 - 4.7k Resistor Network 652-4608X-101-4.7K from Mouser.com (Has an extra resistor, but works fine) 1 - D-Sub 25 pin Male - Mouser, RadioShack, etc. 1 - Barrel power connector - Whatever works for your power supply. (We used a spare 12V power brick) Stranded Cat-5 is sufficient for wiring Terminals and male headers are optional, see the page for the circuit. Heat sinks for the 5804Bs are needed. We used some aluminum channel. Copper clad PC board (We stock up on ebay every so often) Etching solution - Ferric Chloride, etc.