The final topic in this chapter is the use fo a rotary axis. A rotary axis is most often found in the form of a rotary table or an indexing head. The rotary table is a device that can be fastened to the milling table and then rotated to the desired angular position with a G-code. The positioning designation for a single-axis rotary table is the letter A. Some more sophistiated rotary tables can rotate in two axes, which would be designated A and B.
Machines that support a rotary axis typically allow the table to e positioned with both the G00 code for rapid traverse and G01 for linear interpolation, and in canned cycles. When we simply want to rapid traverse the rotary table to an angular position, we are rotate the rotary table and move a linear axis, we would then call this simultaneous fourth-axis interpolation. We make this distinction because many of the CAD/CAM systems are designated as either indexing or simultaneous.
The syntax for programming a rotary table is the same as for rapid traverse and linear interpolation, and a canned cycle- we only need to add the A-word to the block. The rotary axis is simply an addition to the standard code that we are already familiar with.
The rotary aix is easy to use, but there are a few technical points that we must understand when programming. First, the A-axis will ususally have a resolution of 0.001 decimal degrees. We must always remember that as we move farther away from
the center of the axix, the linear error greatly increases. Second, the A-axis can be programmed to move in the positive or negative direction and can use absolute or incremental coordinates.