Do I Need to Be a G-Code Expert With CNC?

Do I need to be a G Code Expert? In a word, no. You will probably need to know how to quickly scan your G-Code if you are having problems during your machining simulation. Other then that G-Code and a CNC program are throwaway programs for the most part. What do I mean by that? Let me explain.

Let's look at a specific design. Let's say a 12" by 12" square. You build your model, run it through your CAM Software and create a CNC Program made up of G-Code instructions to your machine. Say tomorrow the job requirements change to a 24" by 24" square. Do you go into your G-Code line by line and change the code? Most people wouldn't. They would go back into their CAD or CAM program and scale the square up to 24" by 24". Then post-process the job again to get their new G-Code program.

There are some people that would do this editing line by line because the design is simple. Now think of a complex shape and what scaling it up or down would entail. This would include massive changes to it and reviewing it line by line. We are talking thousands of lines here vs. going back and quickly scaling the model and spitting out some new G-Code.

And that is why this is throwaway. Use it over and over when you can, but don't fret over archiving it if something changes. It is much better to make a copy of the design (CAD File) in its original state and save that somewhere. That is much more useful. Post Processing? - Now you have me worried. With all the variations in G-Codes and M-Codes, how will I ever keep it straight? Don't worry about that. The CAM program you choose will have many Post Processors. Post Processors are like translators. They help the CAM Program spit out the right G-Codes for your specific machine. All you have to do is select the right Post Processor before you spit out the code. That is simple.

Most CAM programs have many machine specific post processors already loaded. All you do is go to the list of them and click on your machine to select it. If you build your own CNC Machine, there are generic post processors loaded for different types of machines. Usually you pick a generic one and modify it a bit with a little testing. You are making sure a move in the X-Axis positive direction really means what you want it to mean.

Don is active in CNC Programming and G Code.

G-Code is part of his expertise.

Inexpensive PCs as CNC Machine Controllers

Part I, Utilizing an off the shelf PC as a CNC Controller

There are two main groups that can take advantage of today’s low cost PCs as an effective and inexpensive CNC controller.

• Retrofits to existing CNC machines with outdated or proprietary controls in need of service.

• Shop built and home built CNC machines.

Inexpensive PCs can cost as little as $150.00 and yet provide a dependable and effective CNC machine controller. Some sources to consider for obtaining such a system are outpost.com and dell.com. Oupost.com is an outlet for Fry’s electronics. They have one PC on sale ranging from $150.00 to $199.00. Several have successfully used this PC in conjunction with MACH2 CNC controller software.

Tradeoffs: Price vs. Quality. With the lowest cost PCs there a tradeoff in performance, quality, and reliability. The manufacturers of these machines use low cost hardware in their manufacture and they make compromises in the design of the systems to keep their costs down. Inexpensive hardware translates directly to a higher failure rate and more difficult to obtain manufacturer support. This can be a deciding factor by itself if you rely on this machine for production.

Design compromises which are common in low cost PC have an impact on performance. The primary concerns are: insufficient memory, the use of shared memory, and on-board graphics devices. The primary hardware requirements for a PC based CNC controller are sufficient memory, and sufficient processor speed. You can see that the compromises present in these systems are in direct opposition to the requirements for CNC controller.

At the bottom end of the Inexpensive PC market there are off the self solutions that will function well as a PC based CNC controller. As with all things, you tend to get what you pay for, so the buyer is advised to be aware of the requirements and limitations that are in play.

Part II in this series of articles will examine an alternative to buying an off the shelf solution and explore building a PC to meet your specifications.

Dan Staber a Mechanical Engineer offering design, analysis, consultation, and project management services. Dan is also a licensed professional engineer is the states of South Dakota and Washington. For more information please vist - http://www.qacad.com

dcstaber@qacad.com