Computer-controlled mills have been around for a long time. A CNC tool can be used in many ways for prototyping, reverse engineering and modeling. The sheer versatility of a CNC router in a prototyping setting is nothing short of astounding. With a good CAD/CAM package and a CNC router, it is possible to create master models with the proper draft for secondary operations such as casting, vacuum forming, sheet metal stamping and FRP composite construction.

Sure, it would be much easier to buy a CNC milling machine…but where's the fun in that? After all, an engineer's job is to bridge scientific concepts and their applications, and, as such, engineers often tinker and tend, prototype and play, typically comfortable surrounded by nuts, bolts, valves, motors, G-Codes and engines (if the stereotype holds true).

Why shell out loads of cash on a CNC machine when you can build one yourself for a fraction of the cost? Part 1 of a recent three-part series (written by Will O'Brien) from Engadget shows you how to build a mini-CNC machine for etching circuit boards and making small parts. Main components such as dot matrix printer parts, cutting boards and an affordable DIY controller give you the opportunity to make your very own 3-axis CNC milling machine.

Arguably the best part is that the guide shuns expensive commercial parts (although it does offer suggestions if that is the way you want to go), instead opting to either use scavenged parts or building components from scratch.

Here we offer Engadget's tips for gathering "scrounged, recycled and adapted" parts for building your own CNC machine. This part of the guide walks you through scavenging the stepper motors from dot matrix printers. Please see O'Brien's three-part series at the gadget site for further details and additional visuals for assistance; parts 2 and 3 provide a step-by-step to actually build the thing. We further recommend CNC Zone for all sorts of homebrew CNC information.

Good luck in your parts hunting and machine building!

Parts Hunting
Getting appropriate materials for the project can be a challenge. In O'Brien's case, he used two half-inch-thick cutting boards (from Sam's Club) that cost about $10 each, cutting them with a standard table saw and a circular miter saw. Higher-quality plastics like Delrin can be obtained from a number of suppliers.

Major components of the DIY CNC machine include the following:

• Stepper motors
• Drive positioning screw
• 3-axis stepper motor controller
• Linear slides

The motor is the most important component to determine the construction of your milling machine. While motors can be purchased from surplus houses, the cheapest place to get them is from old dot matrix printers. Apple Imagewriters are among Engadget's favorite sources, as they contain multiple stepper motors. Further, nearly every dot matrix printer has a hardened steel rod that can be useful for the end goal here: to build the CNC machine.

Most motors spin when power is applied, stepper motors contain multiple coils. If the coils are energized in the proper order, the motor will rotate a small amount (i.e., a step). "To simplify your life later on," Engadget recommends, "you'll want to find stepper motors with more than four wires." Four-wire motors usually are bipolar motors. While they produce more torque, they also end up complicating the control circuit. Unipolar is the preferred type of motor for the frugal hobbiest, as they usually have five or six wires and are "pretty easy to work with."

Considering that most stepper motors are labeled, the major points of interest include the voltage, resistance and the number of degrees per step. Knowing the number of degrees per step is vital for configuring the software so it properly controls the machine later on. For a 3-axis machine, at the very least you'll want both the X axis and the Y axis to have identical motors. While it isn't critical if they don't match, it will cause more pains at a later time.

The drive screw is the next piece for O'Brien's project. Commercial units use linear ball screws or linear gears — which are not cheap. Here you can get away with some 1/4-inch threaded rod from the nearby hardware store. In place of anti-backlash nuts, Engadget used 1-inch long 1/4-inch nuts, which are readily available at nearly every hardware store. These produce very little play. Be sure to test the hardware while at the store, as defects in the nut or rod will produce drag "that is easily noticeable by spinning the nut on the rod."

To couple the rod to the motor shaft, parts 2 and 3 of O'Brien's CNC machine-building project use vinyl tubing with a pair of collars. This tubing is 1/4-inch inner diameter and prevents binding by allowing "some play between the rod and the motor."

Says O'Brien:

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: linear slides, which are key to the design of a functional machine. "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. For instance, ShopBot machines the edge of a piece of steel and uses an angled roller bearing for its linear rail. For this project, Engadget used 1/4-inch steel rod from the hardware store and some brass and steel bushings...they don't recommend it.

According to O'Brien:

The brass material slides easier, but ultimately we think the smaller size and unfinished rod is too prone to binding. Alignment is critical, but they can work well for very short travel.

Salvaging matching rods from old printers is more optimal. Imagewriter IIs have metal carriages with pressed-in brass bearings. The cast material is on the brittle side, but some careful dremel work can really pay off.

Once you've bought or salvaged a set of motors (i.e., dot matrix printer), you'll need a controller, which does the following: 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. O'Brien and Engadget sifted through a lot of stepper controller designs in their search for the one that presented the best value.

In the end, they found a design at Electronics Lab 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, such as those from the Imagewriter, O'Brien notes you may need to add some separate power transistors.)

As the parts list at the link is a bit outdated, O'Brien and crew offer the following updated shopping list:

• (3) - UCN5804B - alltronics.com
• (12) - 1N49355 Diodes - Part 625-1N4935 from Mouser Electronics
• (2) - .01uF Capacitors - Part 581-SR155C103KAT from Mouser Electronics
• (1) - 10uF Capacitor - Part 140-HTRL25V10-TB from Mouser Electronics
• (3) - 4.7k Resistor Network 652-4608X-101-4.7K from Mouser Electronics (Has an extra resistor, but works fine)
• (1) - D-Sub 25 pin Male – from Mouser Electronics, RadioShack, etc.
• (1) - Barrel power connector - Whatever works for your power supply; Engadget 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. O'Brien used some aluminum channel.
• Copper clad PC board
• Etching solution - Ferric Chloride, etc.

While in no way complete documentation for building such a machine, the information here may provide some guidance for those who wish to do so. Remember, there is more than one way to build a CNC milling machine (See the additional DIY CNC links below.). But now that you know how to scavenge the necessary materials, you can move on to building Engadget's particular machine — an "unholy marriage of cutting boards and dot matrix printers."

Source

How-To: Build your own CNC machine (Part 1)
by Will O'Brien
Engadget, June 29, 2006

How-To: Build your own CNC machine (Part 2)
by Will O'Brien
Engadget, July 4, 2006

How-To: Build your own CNC machine (Part 3)
by Will O'Brien
Engadget, July 11, 2006

Additional

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