How should a vise be aligned on a vertical milling machine for perpendicularity to the column?

Aligning a vise on a vertical milling machine for perpendicularity to the column is best accomplished using a dial indicator against the fixed jaw. This method provides a precise measurement of the alignment between the vise and the milling machine's axis.

When the dial indicator is set up against the fixed jaw, it can measure any deviation or misalignment as the table is moved back and forth. This allows for fine adjustments to ensure that the fixed jaw is perfectly square with the column of the machine. Achieving this perpendicularity is crucial for ensuring that the parts being machined will maintain the correct dimensions and tolerances throughout the milling process.

Using dowel pins might assist in positioning the vise initially, but it doesn't provide the fine adjustments necessary for precise alignment. A machinist square can give a visual indication of squareness but lacks the precision offered by a dial indicator. Similarly, while employing a dial indicator against the movable jaw can help check alignment, the fixed jaw is the reference that needs to be perfectly perpendicular to the rotation of the cutter and the machine's column. Therefore, using the dial indicator against the fixed jaw is the most effective method for ensuring proper alignment of the vise in relation to the machine’s column.