CNC manufacturers do their best to provide features aimed at satisfying all of their customers. Indeed, some features are important and appreciated by everyone. Features like decimal point programming, radius designation for circular motion, and hole-machining canned cycles can be regularly applied without negative side effects.

Other CNC features are not so benign. The CNC manufacturer may be targeting a niche application, like small lots, repeated jobs, or helping with unique setup-related issues. Misapplication of these features will result in wasted time, efforts, or material. Here, we expose four such CNC features, as well as how and when they could be misapplied. 

Conversational Controls

These controls enable shop floor programming. They are best applied when the machine commonly runs small lots of seldom repeated jobs; relatively simple workpieces with short to medium program execution times; and especially when one person is responsible for everything related to the job, including programming. Many contract shops have machines matching these criteria.

As lot sizes grow and jobs are repeated — with more complex workpieces requiring longer run times and/or when more people are available to help with the CNC process — the benefit of shopfloor programming fades. Companies with this scenario, like many product producing companies, tend to have workers specialize in the tasks they perform. Many tasks are performed in preparation for upcoming jobs while the machine is running the current job. This includes the task of programming. For them, using a conversational control wastes precious machine time.

Tool Length Compensation

There are two ways to use machining center tool length compensation. While programming remains the same for each, operation techniques are dramatically different. 

With one method, the tool length compensation value is the distance in the Z-axis from the tool tip to the Z-axis program zero surface. It is measured during the setup, meaning the machine must be used as a kind of height gauge. This is only appropriate if tool length compensation values must be measured by the operator while the machine is down between production runs, which is often the case in contract shops.

With the other method, the tool length compensation value is the tool’s length. Assuming the company has the resources, cutting tools can be assembled and measured, possibly in the tool crib, while the machine is in production. Tool length compensation value entry can even be programmed, commonly by the tool length measuring device. Related setup time is reduced to the time it takes to load the program and execute it once.

Fixture Offsets

There are two ways to use fixture offsets based on whether setups are qualified. 

The first method is used when work holding setups are not qualified. The setup person must measure the distance in each axis from the machine’s reference position to the program zero surface for the axis. These values are manually entered into the related fixture offset registers. They must be measured every time the setup is made.

With the second method–which should be used when setups are qualified–the program zero assignment values will remain the same from one setup to the next. A programmed command can be used to enter these values into the fixture offset. This second method eliminates the entire task of program zero assignment.

Tool Nose Radius Compensation

With tool nose radius compensation, the CNC programmer uses G41 or G42 to specify the relationship between the cutting tool and the workpiece. The setup person must specify, with offset settings, the type of tool and its nose radius.

This feature and its method of use, work well with CNC programs manually written at G-code level. But when a CAM system is used to prepare programs, the programmer can specify the cutting tool’s nose radius and the CAM system will generate a compensated tool path. This eliminates the need for the operator to make the offset entries previously mentioned, which in turn, reduces setup time and the potential for entry mistakes.

Maximize Efficiency with the Right CNC Applications

Understanding the proper application of CNC features is essential to improving efficiency, reducing waste, and maximizing machine time. Avoiding misapplications—whether in conversational controls, tool length compensation, fixture offsets, or tool nose radius compensation—ensures your shop operates at peak performance.