Toolmaker's vise Question

[mklotz]

The groove is there in case burrs on the edges of workpieces prevent the work from seating solidly (and therefore aligning with) the fixed jaw. What happens is that the burr "slides into" the relief slot; with nothing to butt against it can't influence the alignment of the part.

Look carefully at quality machinists' squares and you'll see a similar relief slot.

Of course, good machinists deburr parts before clamping them in their vises.