All the rotary/pivoting motions are executed by the spindle head of the machine. These machines can be both vertical and horizontal, and they have limited motion. Some machines can change heads, not just tools. Heads can be straight, 90-degree, nutating, or continuously indexing. Some examples are shown in Figure 2-34.

Figure 2-34: Examples of Head/Head machines.

All Head/Head machines have different behavior, based on individual installation settings. Rotary directions, limits, retractions, rotary wind-up, and handling singularities can all be altered from factory settings. The most important basic dimension needed is the rotary/pivot center point, which is measured from the spindle face to the head s rotary position. Machine manufacturers sometimes provide a nominal value, but it is essential that the manufacturer s value be double-checked, especially if it is a nice round number, for instance, 10 inches. The roundness is a good indication that the number is not accurate.

Close is not good enough. Knowing the exact dimension is vital if precision work is to be done.