Program Offset Entries Whenever Possible

Entering data at the machine is usually tedious. Although control manufacturers provide full access to any data that must be entered or modified by the setup person or operator, many do not make it convenient to do so.

Columns From: 8/2/2005 Modern Machine Shop,

Entering data at the machine is usually tedious. Although control manufacturers provide full access to any data that must be entered or modified by the setup person or operator, many do not make it convenient to do so. Additionally, entering data at the machine is time-consuming and error-prone. It is especially costly if the machine is not running production while entries are made.

For example, let's consider the task of entering CNC programs. While it is important that your employees have the ability to modify programs during program verification, control manufacturers did not intend for this function to be used as the sole means for entering entire programs. Anyone entering a long program at the machine from scratch soon realizes that another method of loading programs must be found. Most companies, of course, create programs off-line, using some kind of distributive numerical control (DNC) system to quickly load programs into a CNC machine.

Try to think of offset entries in the same way you would think of program entry. You probably don't expect your setup people to enter lengthy programs during setup, but do you expect them to enter more than just a few offsets? Like entering programs, manually entering offsets is tedious, time-consuming and error-prone.

If you know, or if you can determine the value of an offset before a setup must be made, don't make the setup person manually enter it during setup. Doing so can be just as wasteful as making them enter CNC programs. Instead, find a way to program offset entries. The more offsets that must be entered, the more you'll benefit.

Most controls use a G10 command for offset entry. With one popular machining center control, for example, the command G90eG10 L1 P1 85.0048 enters the value 5.0048 into offset number one. The command G90 G10 L2 P1 X-12.4363 Y-9.3762 Z-11.1827 enters the specified values into fixture offset number one.

In some applications, offset-entry commands can be included in the CNC program that machines the workpiece. To enter fixture offsets for repeated jobs having qualified setups, for example, the G10 commands can be placed at the beginning of the program (though they'll be executed every time the program is run), or you can place them at the end of the program (after the end of program command).

Consider these commands:

N185 M30 (End of program) N999 G90 G10 L2 P1 X-12.4363 Y-9.3762 Z-11.1827 G10 L2 P2 X-16.3734 Y-9.8373 Z-11.23736 M30

During the setup, the setup operator will search to line N999 and execute from that point (like rerunning a tool). The G10 commands will be executed and the program will end. The N999 sequence will not be seen again (unless someone scans to line N999).

In similar fashion, you can include tool nose radius compensation offset entries (for turning centers) in the machining program (at the beginning or the end). These commands enter two sets of tool nose radius offsets, one for a turning tool and the other for a boring bar.

00001 (Program number) N005 G10 P2 80.0316 T3 N010 G10 P5 80.0156 T2

In other applications, it is better to create a separate program to enter offsets. For example, if you measure tool length compensation values for your machining centers off-line, the tool setter can create an offset entering program like this one:

08001 (Enter offsets)
G90 G10 L1 P1 86.2343 G10 L1 P2 88.3476 G10 L 1 P3 86.9233 G10 L1 P4 85.3433 G10 L1 P5 87.3433 G10 L 1 P6 88.7682 G10 L 1 P7 89.2836 G10 L 1 P8 87.6454 G10 L 1 P9 88.3486 G10 L1 P10 85.1038 M30

This program can be loaded during setup from the company's DNC system. When it is run once, all ten offsets for the job will be entered.

You may ask if it is worth it. Your initial response to this suggestion may be that it will take someone just as long to type offset entries off-line as it takes the setup person to do so during setup. However let's remember that time spent performing setup-related tasks off-line is not nearly as valuable as time spent while the CNC machine is down during setup. Even if someone must work longer (or harder) to perform the task off-line, it may still be beneficial to do so.

We've provided three applications for programming offset entries. Can you think of any others that can be used in your own company?

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