It's common to produce 2 post processors for a 4-axis machining centre. One for "Indexing" programs using workplanes & One for "Rotary" programs.
For Rotary posts it is common practice to draw the component in 2D (flatland) and then use a calculation in the post to convert AY variable values to A-axis Angular values as follows...
A-axis Angle = (AY*360)/(PI*DIAMETER)
...where DIAMETER is a billet dia. value input by the programmer.
However, recently I installed AlphaCAM with a Fadal CNC 88HS control where a simple line...
G17 Qx.xx
...at the top of the program did the conversion automatically.
The Q value is calculated is follows...
Q value = (A-axis Ratio)/((5*PI*DIAMETER)/25.4)
...where
DIAMETER is input by the programmer.
A-AXIS RATIO is a constant on the machine related to the gearbox. This is a value typically 90 to 1 (the machine manual has the data for A-axis Ratio).
This line allows you to write a post processor in X[GLX+AX] Y[GLY+AY] format with a simple "Rotary or Index?" question at the top of the post processor. The post covers both types of programming in one.
Andy Hadley
