Your CNC machine is made for cutting and drilling parts that you design yourself. Yes, you can easily download G-Code projects from the Internet, but the only real way you're going to become familiar with the operation of your CNC machine is to begin designing your own parts, converting them to G-Code using a CAM application, and then using Mach3 (or other Control software) for letting your machine get to work.

You can find CAD software all over the place-as many free versions exist for download on the Internet as there are commercial versions that will cost you anywhere from a small to a large fee. While the price of software isn't always an indicator of quality, software that comes with a price does usually come with technical support. With free software, you'll find that "tech support" likely comes in the form of posting questions on a discussion forum and waiting for someone to respond with a good answer.

Many of the well-known CAD applications are expensive for the traditional hobbyist-these apps often come with more features than you'll ever put to use. That's why we recommend starting out with a low-cost or free CAD application. Use it until you find it doesn't provide a feature or ability that you need; when that roadblock appears, you'll have to do some research and find a CAD application that does provide the feature(s) you need.

For a great list of CAD software, visit www.freebyte.com/cad/cad.htm, where they've put together a collection web links for free and commercial CAD applications. Plan on doing some Internet searches to obtain reviews and comments from others who have used a particular CAD application.

A few other web sites devoted to CAD that you might want to look over include

http://en.wikipedia.org/wiki/Computer-aided_design: This Wikipedia article provides a brief overview of CAD, as well as links to many more articles of interest.

www.caddprimer.com: You can download the first 70 pages of this book for free to see if it may be useful to you.

http://avocado-cad.sourceforge.net and http://brlcad.org: These are two open source software CAD applications; they're free to download and use with no restrictions.

http://usa.autodesk.com: This is the home of AutoCAD, considered by many to be the industry standard for CAD applications. It's expensive, but always on the cutting edge of features.

www.cnczone.com: Not only is this a great CNC machine web site, but it also has a discussion forum and plenty of product reviews of software and hardware.

As with CAD software, CAM is another type of CNC application that you'll need to investigate. Not only does CAM software convert your CAD designs into G-Code, but it's also responsible for generating the tool path-the controlled movement of your CNC machine's router. CAD software can reduce the amount of time your CNC machine is working by calculating the most efficient path for moving the router.

Point your web browser to www.probotix.com/cnc_software and scroll down the page to locate a list of CAM software for you to investigate. (You'll also find links to CAD, Control, and other CNC-related software and instructions.)

A few other web sites devoted to CAM that you might want to look over include

www.cambam.co.uk: CamBam is a CAM application that's free to download and use; it has a strong following among CNC hobbyists.

www.vectric.com: VCarve and other titles from Vectric may be a bit pricey, but have some great capabilities.

www.bobcad.com: BobCAD offers a free-to-try download of its popular CAM software.

We mentioned the emergency stop, often called an EStop, in Chapter 18. An EStop is a useful button for quickly shutting down your CNC machine. It's not the same as the CNC machine's power button, which may be located under the machine or otherwise not easily reachable. In the event of an emergency-such as your CNC machine hitting a knot of wood or a motor getting locked up-you want to be able to quickly shut off your machine; imagine trying to find the power button on a power strip that's under the table or out of reach, and you'll begin to understand the value of putting an EStop on your machine in an easy-to-reach location.

Installing one is fairly simple, and we'll walk you through the installation in this section. You'll want to locate and purchase the type of EStop that allows you to twist the top of the button so it releases and pops up; when the button is pressed (or quickly hit), the button stays down and won't pop back up until you twist it again to release. If you're having trouble locating one, contact www.acksupply.com to purchase the one shown in the following figures.

Figure 19-1 shows the items we used to create our EStop (minus the wiring).

We drilled a 1" hole in an aluminum bracket for the button and two 1/4" holes so we could bolt the bracket to the front of our CNC machine. The small black metal ring and square aluminum ring are used to secure the button to the bracket from underneath; they screw onto the button and hold it tight.

Figure 19-2 shows the bracket bolted to the front of the CNC machine.

Figure 19-1. The components used to add an EStop to the CNC machine

Figure 19-2. The bracket mounted to the front of the CNC machine will hold the EStop button.

Next, insert the button into the bracket through the square metal ring and into the hole drilled for it on the bracket. Use the round black ring to tighten down the button from underneath the bracket, as shown in Figure 19-3. Cut two pieces of wire (one black and one white) long enough to reach the breakout board. (We cut the lengths and ran them through the conduit for the x-axis motor wiring.)

Figure 19-3. The EStop wired and ready to be connected to the breakout board

On the bottom of the EStop, you'll see three metal posts, labeled G, NO, and NC. G is for ground; solder or connect the white wire to the G post and connect it to the Ground port on the breakout board. The NO label means normal opened, and NC means normal closed; these simply represent whether the switch is considered pressed (closed) or not pressed (open) when the power to the machine is turned on. Solder or connect the black wire to the NO port on the EStop button and connect the other end to port #10 on the breakout board. Figure 19-4 shows a closeup of the breakout board with the two wires coming from the EStop button labeled.

Figure 19-4. The wires from the EStop button connect to the breakout board.

Next, go back into the Mach3 software and set the EStop value to 1 (on) if it is set to 0. (Refer back to Chapter 18 for the location of the EStop configuration.) Run a test by entering some G-Code to spin one of the motors; while the motor is turning, press the EStop button, and the motor should immediately quit rotating. If it doesn't, check your wiring again for the EStop button as well as the Mach3 software setting.

As you become familiar with CAD software, you'll likely discover that there's no real standard for where to start a milling job. Some CAD operators start in the middle of a piece of material, with the (0,0) coordinates for the x- and y-axes as close to the center as possible. Others will set the (0,0) starting coordinates in one of the corners. You'll probably find that the starting position of your router will depend on the job you're performing.

Many CAD machines will have a set of limit switches (see Figure 19-5) to help define the starting position. Limit switches, when wired properly, send a signal to the breakout board telling the motors to stop spinning. A small arm on the limit switch, when pressed, sends an electrical signal to the breakout board, indicating the switch has been engaged.

A limit switch can be helpful for ensuring that a motor (such as the x-axis motor) doesn't move the router too far and try to go beyond the tabletop's working surface. Limit switches can also be used to define the (0,0) point on a table. For example, if you place one limit switch on the front leg of your CNC machine and a second limit switch on the left gantry, you can manually move (or use a program to move) the router to the front-left corner and define that point as (0,0) in your CAD program.

Figure 19-5. Limit switches can be used to quickly stop the router's movement.

You can find more information on adding and using limit switches at www.buildyourcnc.com/book.aspx, as well as search for more information in the book's forum at the same address.

Although beyond the scope of this book, adding additional safety features such as limit switches and an EStop is highly recommended. One additional safety feature that we'd like to quickly mention is called a solid state relay (SSR).

You can find more information and discussion of SSRs at www.buildyourcnc.com, but in a nutshell, an SSR is a useful device for controlling the startup and shutdown of all your CNC machine's electronics. An SSR can be used to turn on and off the router (so you don't have to turn it on manually before beginning a job), as well as disengage the motors until the program is initiated. One added benefit of the SSR is that when you turn on your machine's motors, motor drivers, and breakout board, the SSR can be used to prevent the electronics from accidentally starting up if a program is running.

Whether you use your machine often or rarely, give serious consideration to adding an SSR to your CNC machine for added safety.

MDF is a great material, but it's very sensitive to water. Under no circumstances should you set a cold drink on any MDF surface! Try to keep the machine in a cool, dry location and avoid putting it under or near any source of condensation or leaks. Water will cause the surface of the MDF material to swell and deform.

One good way to protect your CNC machine's MDF parts is to paint them. The downside to this is that you'll likely need to tear down your machine, paint the parts, and reassemble. Spray paint or a good coat of latex will both work-just don't put it on too thick.

Our goal with this book was to give you the best instructions possible for building a working CNC machine, and we hope we've accomplished that task. Now it's up to you to push your machine to its limits and see what you can do with it. You'll find the book's web site and discussion forums a good place to talk about your machine, see what others are doing with their machines, and maybe offer some advice to those just getting started with the book.

We want to see and hear from our readers, and we hope you'll take the time to register at the book's forum (www.buildyourncnc.com/book.aspx) and share a picture or two of your final machine-tell us about the work and any modifications you've made, and of course let us know if we've made any errors so we can fix them and inform others on the errata/corrections page found at the same web address.

Be safe, and have fun with your very own CNC machine!