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Almost all current model machining center controls use fixture offsets for program zero assignment. With most, the distance from the machine's reference position (commonly called the zero return position) to the program zero point must be determined for each axis.
All current CNC controls have a special program verification display screen page that shows a few upcoming commands in the CNC program, the current absolute position, the distance-to-go and currently instated G and M codes. Many control manufacturers refer to this display screen page as the program check page.
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.
In my last two columns, we covered steps one and two of verifying CNC programs. Now, let's move on to step three: verifying the correctness of the first workpiece.
In last month's column, we explored the first step of verifying CNC programs. Now we begin a new chapter: step two.
All CNC programs must be verified. While new programs present more challenges than proven programs, operators must be careful and alert during every step of a program's verification.
Companies vary when it comes to how they use CNC people. In some companies, such as contract shops, one person is responsible for the entire CNC job, including programming the job, setting it up and running production.
Every dimension specified on a workpiece drawing has a tolerance—either explicitly specified with a tolerance band or implied in some manner. Explicit tolerances are specified in different ways (plus or minus a value, plus one value or minus another, or high limit and low limit).
Older model Fanuc controls and some current model Fanuc-compatible controls have a feature to help you machine round counterbores with an end mill (G12 and G13). For some reason, Fanuc stopped providing these helpful G codes.
When verifying a program, the most crucial time is when each tool approaches the workpiece for the first time. This is true for both machining centers and turning centers.