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24.09.2018

The best CNC Programmers also know how to edit Post Processors

The best CNC Programmers also know how to edit Post Processors Author: Colin Gilchrist, CNC Programming, Training, Post Processor and Simulation Development

What is a Post Processor?

I've been using CAD/CAM systems to program CNC Machines since 1997. By far the most important skill I've picked up along the way is the ability to make edits to a Post Processor. But what is a Post Processor? A Post Processor is a software script that is used to convert the generic CAM program into NC code that is formatted with the proper Syntax for your machine. Understanding how to make the post processor output the proper code for your machine is a critical part of the program creation process. I've met so many different CNC Programmers over the years. The "best" of them have one thing in common; they know something about how to edit the post processor to get proper NC code for their machine.

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The Post Processor is the fundamental link between the work you do inside your CAM system, and the machine that is removing the metal. Without a properly formatted post processor, you must resort to making hand-edits to your NC code. This is an error-prone and dangerous process. Making hand-edits to your NC code breaks the link between the CAM program, and the code being run on the machine. Without having a properly configured post processor, your company is playing with fire. It is a matter of "when", not "if" there will be an error introduced into your NC code.

All CAM systems use some form of Post Processor, so make the effort to learn how they work, and how to edit them. I've seen many companies over the years that rely on their Reseller or a 3rd-Party Post Builder to obtain their posts. In reality, there is nothing wrong with using this business practice. There are many honest and reliable Post Developers in the CAM business, but I'd also provide a word of caution. Post Development is not "easy". You've got to know the CAM System itself (how the data is created in the "generic" format), the Post Language that is used by the post processor, and the proper syntax for the NC code that will be run on the machine. A break in this chain can spell a headache, or in some cases a disaster. There are many CNC Programmers that "hack" the post processor, to get the code they need "right now!". On the face, there is nothing wrong with this method.

What a Programmer Does Then?

The programmer makes an edit, and then posts the NC code for the current job they are running. Because the edit they made worked (in this case), they go on about their day, not realizing that they have broken some of the code that may be needed for a different job later on. They only discover their issue down the road, when a new job comes in that differs in the code needed, and they end up hacking away at their post, to get this new job done. I've seen shops that have dozens of Post Processors created for the same machine. This is not only inefficient, it is dangerous. There should really only be a single post for each machine in the shop, and this post should be modified for the way your company produces its parts.

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The hidden costs of not having a reliable post are huge... Post Development is not easy. Most CAM Systems on the market today are quite complex, and the script that is used to generate your NC code can be even more daunting. But at the end of the day, an investment must be made to produce reliable NC code. I can't tell you the number of shops I've been in where the Post Processor is basically an afterthought. They will spend hundreds of thousand, if not millions of dollars on high-end CNC equipment, but expect the post to be free, or nearly free. In many cases, a quality Post Processor (purchased from a reputable company, that stands behind their work), costs between 1-3% of the purchase price of the machine. That's right, one to three percent, sometimes less than 1%.

How Much do We Lose?

Take a high-end 5 Axis Japanese machine, that might cost $500,000 fully equipped. The cost of a typical 5X Post, that has been properly modified to support the advanced features and functions of this machine might cost in the range of $3,000 to $7,000, depending on the level of customization required. While $5,000 certainly sounds like a lot of money, that pales in comparison to how much time your CNC Programmer might waste on a yearly basis, making the same hand-edits, over and over again. In addition, the right code, put in the wrong place, can easily crash your half-million dollar machine, and could possibly damage your spindle, to the tune of $20-60K for a replacement. (Not to mention the wasted time waiting for the necessary repairs.)

If your shop rate was $100 per hour (usually more for high-end equipment, but let's use that number for our example), and you run 2 shifts a day, that's 16 hours of billable time per day. So assuming 80% up-time (not unreasonable in this day and age), that is 12.8 billable hours in those two shifts, or $1,280 per day. If you run 5 days per week, that is $6,400 per week that could potentially be lost, waiting to get the spindle repaired. (More if your shop rate, up-time, or days per week are increased...)

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Plus, hand-editing produces anxiety. Besides the potential downtime from a crash, making hand-edits takes valuable time away from your Programmer, and increases their stress level. Let's assume that you are a CNC Programmer, and you create an average of 20 programs per week. And that you spend an average of 15 minutes making hand-edits to those programs. That is 5 hours per week that you would spend on hand editing your code. I think that is probably a very low estimate for the average programmer making hand-edits, but it serves as a good example for now, so let's stick with it. Based on an average of 50 weeks per year (can't forget vacation), that would equate to 250 hours per year of time spent hand editing the NC code.

If we assume a fairly low "burdened rate" of $40 per hour (hourly wage, plus the cost of benefits and taxes), that equates to $10,000 per year of wages paid, just to hand-edit NC code. Now, most 5 Axis Programmers that I know probably have a burdened rate that is easily twice that amount, factoring in their higher hourly or salaried rate, plus the benefits and taxes. This isn't a one year cost either. This is an ongoing expense, day after day, year after year.

Finally, hand-editing breaks the link between the CAM Program, and the NC Code. When you make a hand-edit to a NC Program, you have broken the direct link between the CAM Program that produced the motion, and the NC code that is producing your part. All of a sudden, you have introduced the necessity of "tribal knowledge" needed to make NC code. What happens when the original programmer leaves your company, is out sick, or gets into a car accident? Now you've got to get someone inside your company to take over the reins, or you must hire someone new, and they are stuck trying to figure out the process that was used by the old programmer to produce the NC code. This is a recipe for disaster, and can be avoided by having a properly configured Post Processor in the first place.

So What is the Solution?

Fortunately, there are many options when it comes to post processors. There is really no "one size fits all" solution, and will depend on your shop's work-flow, personnel, and capital resources. But some suggestions for addressing the issue are:

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When purchasing a new machine, make the Machine Tool Builder responsible for providing the post. This is as simple as adding a line-item to the quotation, but be sure the language is specific on what you expect for delivery.

Develop a relationship with your CAD/CAM Reseller, or 3rd-Party Post Developer, and have them quote the necessary post development for new or existing equipment. While this can be expensive, it can also mean some seriously increased productivity, and reliability. It also takes the burden off your existing CNC Programmers for making them responsible for Post Development.

Invest in training one or more of your CNC Programmers to learn Post Development, so that you have the necessary skills "in-house" to make the necessary post edits. While this can be expensive as well, I prefer to think of it as an investment in your company's capabilities, and consider it a competitive advantage. Consider a 3rd-Party Post Solution. There are several companies that develop their own Post Solutions (as opposed to a "native" CAM Post Processor that is specific to a particular CAM Software). While this can also be expensive, often the Solution is bundled with Simulation and Verification Software. In addition to creating the NC Code, you can simulate and verify the code "virtually" inside their software package. One advantage of going this route is that many of these solution can take source "input" from more than one CAM package. So if you've got several CAM solutions being used, this custom Solution can tie them all together in one package.

Above all, don't wait until a machine is down, or there is a problem on the shop floor to consider the issue of Post Processors, and how they are a critical link in your process chain.

Commentary from Dreambird

Not only a postprocessor is a complicated matter, it is also unique for every machine tool. Even if you have two machine tools from one manufacturer to make the same operation with different sets of tools and auxiliary devices, they shall have different postprocessors compiled. That's why postprocessor preparation should be considered seriously.

Radan is a CAD/CAM system for NC code creation for various sheet metal fabrication operations: bending, punching, laser cutting, five-axis machining and tube cutting.

A machine tool is only as efficient as the software driving it, so that is why the Radan support team personally installs all the post processors to ensure that they are commissioned to match the customer's machine tool and controller. Understanding the sophistication and the limits of each machine tool individually is the key to driving it efficiently; Radpunch will assist your operators to optimize your manufacturing capacity to within those limits for all of your machines.

Dreambird offers postprocessor development for Vero Software products: Radbend - Radan's sheet metal bending module, and Edgecam CAD/CAM solution for milling, turning and multi-axis CNC metalworking, following the customer's requirements and manufacturing processes.





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