Getting Started with CNCComments (0)
This article is from Issue 101 of Woodcraft Magazine.
A newbie’s guide to your electronic shop helper
CNC (Computer Numeric Control) technology is becoming more and more affordable. That’s not to say these machines are cheap, but for the investment of two to three thousand bucks, you can employ a quite capable workshop assistant that can do a lot for you, including creating signs, shaping templates, making parts, cutting joints, and even carving forms. Once you get the hang of using it, you’ll be amazed at what it can do. The learning curve is not as steep as you might imagine, and plenty of online resources and forums are available to help when you have questions.
In woodworking, the vast majority of CNC machines available are routers with several components that make them work, including the machines themselves and the computer(s) that drive them. The computer part usually involves two software programs responsible for making the router move. With one program, you design tool paths (a series of coordinate locations that the router will follow) and the other communicates those paths to the router. While there are some proprietary differences in the machines from individual manufacturers, they all work about the same way. Once you learn the quirks of your new shop assistant, you’ll be creating great projects in all kinds of exciting and time-saving ways.
Meet your new assistant
With a few exceptions (see The Non-Gantry Option below) CNC machines are gantry-based. The gantry is a horizontal bar that holds a router and rides above the machine’s table, which supports your workpiece. Most machines can move the router in three directions: side to side across the gantry (the Xaxis), along the length of the table (the Y axis), and up and down (the Z axis). Depending on the work you’re doing, you may want to cover your machine’s table with a “spoil” board, a sacrificial piece of sheet stock such as MDF to act as a backer for when you cut all the way through your workpiece. When this board becomes worn out, you can either replace it or use the router and appropriate bit to resurface it. To speak the same language as your high-tech helper, you’ll need to navigate a couple pieces of software, which we’ll delve into on the pages ahead.
Gantry-based router. A CNC machine can accommodate a workpiece only as big as its table. This machine, with its 12 × 24 table, is a great choice for sign making and smaller projects. Larger machines can make things as diverse as cabinetry, boats, and even buildings.
Router vs. spindle. Depending on the machine, you may have a choice as to what drives the bit. A regular router (left) is less expensive upfront and easier to replace. A spindle (a specialized, liquid-cooled motor) is quieter and capable of constantly running for hours at a time—often necessary for three-dimensional carving jobs.
The Non-Gantry Option
A few CNC machines on the market don’t use a gantry system. Three of the more prominent manufacturers include Shaper Tools, Maslow, and CarveWrite. Shaper Tools (shown below) offers a hand-held CNC router that relies, in part, on the operator to move the tool across the work surface. Maslow’s router moves across an inclined worktable suspended from two cog-driven chains. And CarveWright’s offering looks and works like a portable planer, moving the workpiece through the machine via a roller system.
Controlling your machine
The first piece of software to navigate operates your machine, allowing you to position the router’s bit so that it starts cutting in the right place. This program also tells it what file you want to run. Some CNC machine manufacturers require a separate computer to run the software, while others have it built right into their machines. If your machine requires a separate computer, consider investing in an inexpensive or used laptop for dedicated CNC use. Control software doesn’t require a lot of computing power, and having a shop laptop keeps your good computer away from the dust. While using a regular computer grants you a bigger screen to control the action, it can be cumbersome as you make the final tweaks to the bit’s position. The machines with built-in control software often rely on a tiny keypad, or pendant, (a hand-held control pad) for input, allowing you to get much closer to the bit as you position it. Both systems work well, so choosing is more a matter of preference.
Before proceeding, you should know a little about how a CNC machine “thinks.” It functions using Cartesian coordinates. (Remember graphing Xand Y equations in math class?) Fortunately, however, there isn’t a lot of complex math involved here. Imagine the machine’s bed (or table) as a piece of graph paper. The width of the table is the X-axis, and its length is the Y-axis. Every point on the table can be identified by Xand Y coordinates. When you program a CNC machine to make a cut, you are essentially saying I want you to move the bit from point A to point B to point C (and so on). The movement of the router is controlled by what is called G-code. This is a computer language that lists all the coordinates for where you want the bit to go. Consider G-code as a liaison between the design software and the control software. While you can write your own G-code, you don’t have to. In fact, you don’t even have to understand it; most people opt to use a design program that writes it for them.
Using a pendant. For routers equipped with a pendant, setting up to cut is much the same as with a laptop, though you’ll probably just have buttons to push instead of clicking on icons with a mouse. The mobility of a pendant allows you to hold it near the bit as you position it.
Lots and lots of numbers. The G-code for even a relatively simple part can run hundreds, if not thousands of lines. Each of these lines essentially says move from here to here.
While many manufacturers provide stock projects with their machines or downloads from their websites, you may eventually want to learn how to design your own parts. And even if you simply download the CNC files offered through the Woodcraft website, you’ll still need to know how to prepare them for use. This is where the second piece of software comes in: a design program. There are several on the market, and your machine probably came with one. One of the most popular design programs is Vetric’s V-Carve, which allows you to save tool paths for nearly any CNC machine on the market. If your design software is not resident on the computer you use to control your CNC machine, or your CNC machine is controlled with a pendant, use a flash drive to transfer the files.
Define and draw. To make a new design, you must first tell the program how big a piece of material you’re using and where the origin is. Most of the time, the center is a good place. Then you can draw the desired shape(s) to be cut, such as for this small box.
Assign toolpaths. Once you have your part drawn, you assign toolpaths to the various lines that make up the drawing. Two of the most common types of toolpaths are Profile and Pocket. You might think of a Profile toolpath as a cookie-cutter, whereas a Pocket toolpath is more like a scoop. When you assign toolpaths, you can choose the type of bit, the depth of cut, and so on.
Check and export. After assigning toolpaths, design software V-Carve allows you to simulate the cuts on your computer, so you can see exactly what you’ve told the router to do and in what order. Once you’re happy with the result, you export the toolpaths as G-code that your machine will understand.
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