Explain how to use a dial indicator to align a vise on a CNC milling machine table to ensure perpendicularity.

Using a dial indicator to align a vise on a CNC milling machine table ensures that the vise's jaws are perpendicular to the machine's X or Y axis, which is crucial for accurate machining. First, securely mount the dial indicator on the machine's spindle or a rigid holder. Ensure the indicator's stylus is long enough to reach the vise jaw. Next, mount the vise loosely on the milling machine table. Do not fully tighten the mounting bolts yet. Position the dial indicator's stylus against the fixed jaw of the vise. Ensure the stylus is perpendicular to the jaw surface. Then, zero the dial indicator. Rotate the indicator's bezel to set the dial to zero at the starting position on the vise jaw. Next, move the machine's table along the X or Y axis (depending on which axis you are aligning the vise to), traversing the dial indicator along the entire length of the vise jaw. Observe the dial indicator reading as you traverse the jaw. The reading will indicate the amount of deviation from perfect perpendicularity. Tap the vise gently with a soft-faced hammer to adjust its position. The goal is to minimize the total indicator reading (TIR) across the entire length of the jaw. Repeat the traversing and tapping process until the TIR is within the desired tolerance. A TIR of 0.0005" over the jaw length is typically considered acceptable for high-precision work. Once the desired alignment is achieved, securely tighten the vise mounting bolts. Retest the alignment after tightening the bolts to ensure that the vise has not shifted during tightening. Even small shifts can throw off the alignment. This ensures that the workpiece, when clamped in the vise, is accurately aligned with the machine's axes, leading to accurate machining.