Varying Accuracy

Every day across the country CNC machines are roughing and then finishing components - this might seem like a basic statement, but consider how it is being done, or more specifically the accuracy with which the cutting tool is being moved. By its very nature, the roughing operation is essentially a stock removal process - removing the maximum material in the shortest time, so is it necessary for the cutting tool to be positioned to micron accuracy? In most cases the answer is going to be no, meaning a proportional increase in feedrate is possible and the result is a shorter cycle time and an increase in profit.

Haas software engineers have designed into the Haas control a facility called Maximum Rounding and it can be accessed through Setting 85. Its function is to allow the user to define the machining accuracy of rounded corners within a selected tolerance. The default value is 0.05" but it can be set to zero in which case the machine will treat all corners as if an Exact Stop was required.

However Setting 85 is only a default value and the user has the ability to override this figure using a programmed command with the G187 code and specifying an E value.

For example G187 E0.5 would set the Maximum corner rounding value to 0.5mm for the duration of the program and will be cancelled whenever “Reset” is pressed, M30 or M02 is executed, the end of program is reached, or E-stop is pressed.

Most CAM system post processors can be adjusted to automatically output a G187 for a roughing cycle and then alter the value again when the finishing cycle is run. The result is a shorter cycle time, more accurate and consistent parts and extended cutting tool life.