I Learned Something New Today About Machining

When telling your program where your coordinates are, using the left edge of the mill vise jaws as 0 is pretty obvious.   Using a workpiece stop like this also means every part up against that bar will be in the same relative position. 

While watching Blondihacks videos about machining  (often very funny, although not as consistently as This Old Tony), she mentioned something that was in the "Duh" category but I never thought about it before.  The rear fixed jaw is always in the same relative position unless you remove the vise from the mill table.

Why this matters: if I remove a workpiece that is 3" wide in Y and put in a workpiece that is 2" wide in Y (or worse, 2.2678" wide), I need to use the edge finder to determine where Y=0 is located so that I can set that location as zero.  All my programs have relied on Y=0 being at the front movable jaw.  Every change of workpiece width means another rwe moving a cutting tool to put on an edge finder and back again along with a bit of + and - with X, Y, and Z to find the spot where the edge finder stops jumping away from perfectly round so that I can mark that location as Y=0.

It is certainly simpler to think of a part with Y always going from 0 to the y coordinate.  Thinking of Y going from 0 back to Y coordinate will save a lot of time setting Y=0.