CNC Tips and Techniques. Peter Smid
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time to make fixes at the machine, even a new program, without anybody’s knowledge. Some programmers/operators may feel self-satisfied or even complacent; they stop learning new methods and techniques. Others may have exaggerated demands in terms of wages, benefits, time off, and so on.
One item that needs consideration is the method by which the part program is generated. It is still common in many shops to write the program manually rather than using a CAD/CAM programming system. Although is it important for the programmer to understand manual programming, it is equally important for the shop manager to understand the benefits of a CAD/CAM (also known as CAM) programming system. For the combined position of one person programming and operating, a CAM system installed in the vicinity of the CNC machine may bring many benefits, in spite of its initial cost.
A number of machine shop managers prefer the CNC Programmer/Operator position and are well aware of its drawbacks. If established in a suitable environment and managed properly, having a multi-skilled worker in the shop should bring in more benefits than problems. The majority of CNC programmers who also operate the CNC machine are honest and dedicated; they do their best to do the job well. They consider themselves true professionals, and rightly so. On the management side, a prudent owner or manager has to consider all pluses and minuses before creating the position of a CNC Programmer/Operator.
 | Using CAM Software in Small Shops November 2004, updated February 2013 |
Over the years, manual programming has offered many benefits to CNC programmers. It offers absolute control over the toolpath and it teaches lessons in organization and discipline. Also, it does have some negative side effects; it is very time consuming, prone to human errors, and hard to make changes in the program. The need to eliminate — or at least minimize — the problems associated with manual programming led to the development of CNC programming using computers, known as CAM programming.
CAM SOFTWARE
Modern CNC software — typically called CAM software because of the many trade names ending with the three letters CAM, such as the popular Mastercam — offers many features that automate the original manual method of programming. Computers produce most CNC programs more quickly and more accurately than manual programming ever did. A proper application of CAM software will produce a part program that reflects the programmer’s way of machining a part.
Whether developed manually or generated by software, the part program has to be in a format compatible with the CNC machine control unit. Comparing manual programming with CAM programming is not fair; however, the knowledge and understanding of manual programming techniques is important in all CAM applications.
Small shops are not like big companies. Their needs are different and so is their management style. Desktop or floor-based CAM programming is not new — it has proven itself in many machine shops. Software development has been steadily improving. Many simple and even complex programming applications are available for much lower cost than only a few years ago.
What Is Involved?
Hardware is the physical parts of CAM. However, hardware is not the focus of this article — it changes so rapidly that something new will be available by the time you read this. Software ages as well, but at a somewhat slower rate. There will always be new features and updated ones added, inviting new customers to purchase and current customers to update. As long as the software does the job, some shops may work with the same version for many years.
A few years back, the subject of hardware consideration for CAM work could be suitable for several articles. Now, most concerns should focus on the processing power, RAM (temporary Random Access Memory) and the graphics card/display combination, even the hard disk capacity. In all cases, the bigger the specification number, the better choice. CAM software has been developed mostly for the Windows operating system, although some software does exist for the Apple operating system.
One piece of hardware — a CD or DVD reader/writer drive — is now part of every computer and serves as an inexpensive method of safely backing up valuable data. In addition, other inexpensive back-up accessories are available such as flash drives and external hard drives. If a direct connection between the CAM system and the CNC machine is desired, some CAM systems offer a file transfer option. For a more complex dedicated DNC transfer, separate software is usually a better choice. Display is also very important — looking extensively at a computer screen can be tiring at best and may cause physical problems over time. Large viewing size and high resolution monitors are critical for comfortable work. Many graphics cards are made for gaming and may not be suitable for serious CAM work. Other features such as hard drive size are no longer a problem, as long as they are reliable and well maintained.
PROGRAMMING ENVIRONMENT
A typical working environment within CAM software can be easily summed up in three steps:
1. Toolpath Geometry
2. Toolpath Application
3. Program Generation
Depending on the software, many intermediate (or additional) steps may be available, but the three basic steps will always apply.
Toolpath Geometry
Toolpath geometry is a visual representation of the toolpath itself. It is always generated graphically, using points, lines, arcs, and other entities. True toolpath geometry is called an associated geometry — that means a change in either the toolpath or the operation will change all related data automatically.
Even the lowest priced (i.e., featured) CAM software offers the most common 2D toolpaths — drilling operations, contouring, and pocketing. More sophisticated software will also include special toolpaths and operations, such as helical interpolation, splines as part of the geometry, special cycles, subprograms, 3D machining, surfaces, and solids. When selecting CAM software, think also of future needs, such as the type of future work, as well as machine and control features.
Toolpath Application
Once the tools have been selected, a particular tool is applied to the selected geometry. The tool description not only identifies the tool dimensions, it also contains additional information, such as speeds and feeds, clearances, and offsets that are associated with the tool.
Program Generation
Generating a CNC part program is the last step in the process. In order for the process to match a particular machine and control system, the original processing has to be processed again — it has to be reformatted as per control specifications. This step is called post processing. A high quality post processor is one of the most important features of CAM programming software. The purpose of the post processor is to format the generic database into a part program that can be used on a CNC machine. CNC software vendors always include several post processors with their software. Keep in mind that these are generic post processors for the most common controls. In order to make them work in a specific way, post processors often have to be customized.
Some amount of customization is usually necessary. A qualified CAM programmer may optimize or customize a post processor or may ask the software vendor or an independent consultant to do it for a fee.
Customizing a post processor includes several steps, such as entering the known data about a machine tool, relevant data of the control system, such as format of the program, various commands and functions, use of the decimal point, etc. The program structure (or program template) is also part of a successful post processor. The format determines the order of tool sequences and machine activities (for example, the coolant).
Other Features
Combining part geometry with the tools used creates an operation. Operations are treated as units — within a unit, an individual change will update the whole operation, for example, changing a tool diameter, spindle speed, or a cutting feedrate. There could be a number of special features included in CAM software. One that is very important is the support for various cycles for drilling, milling, turning, grooving, and threading. Such cycles