The Total Indicator Run out, or TIR, is an important component of any plastic machining operation. Plastic drill bits and router bits cannot function properly if the machine's TIR is out of balance. There are several plastic machining components that must be checked for TIR, including the spindle, the spindle mount, and the colleting system. In order to verify the TIR, the required tools include a .001? dial indicator (or better), a magnetic indicator base, a 6? indicator stand assembly (or longer), a long shank solid carbide tool, and a blank drill rod or blank solid carbide round.

The first test to do in the plastic machining system is in the spindle taper. Manufacturers should be able to tell you what an acceptable TIR is, although it's usually .001? or better on an older spindle or .0005? on a newer one, without any play in the radial direction. The rod inserted in the collet can then be used to measure the TIR at the furthest point from the spindle. This should be done several times, since the TIR can vary depending on how the taper, collet, chuck nut, and rod align, and the maximum reading should be used. The colleting system should have a better than .002? total TIR if it is older, or .001? total TIR if it is newer.

Now that these two verifications have been completed, there is another test that can be done if the plastic drill bits and router bits used in the machine will be involved in any surface milling, pocketing or lettering. If this is the case, the spindle should be verified when it is perpendicular to the work surface. Any spoil boards must be removed, and the indicator should be set to determine the amount of tilt that the spindle mount has in both the X and the Y-axis. This shows the degree of apparent machining marks that will be seen on the bottom of a pocket cut.

The final verification of TIR involves a very precise procedure, though. The dial indicator must be mounted in the spindle and zeroed on the main table surface. At this point you can rotate the spindle 180 degrees by hand and record the amount of TIV along the X and Y-axis. A larger Total Indicator Run out means that there is more delineation that will be seen during parallel pocketing cuts.