Having worked from prints for what seems my entire life, it wasn't uncommon
for me to redraw (on scratch paper) and re-dimension parts so they were
meaningful in the way they'd be made. No changes were introduced, just
dimensions provided in a way that was useful. By working to nominal
dimensions at all times, you are able to use any portion of a machined piece
as the datum point. That's important when you start changing reference
points.

I taught a short class to a bunch of design engineers and techs. One
major point was to dimension the parts in the way they were going to be
inspected. Picture a 3 hole group where two of the holes were
dimensioned from one end of a 6' long tube with a sweep bend in the end,
the other hole from the other end. Since there were more dimensions
involved, it was a lot of math to get to the desired hole spacing. Why
not just dimension the parts as a group? It was easier to snap the lines
on the CAD system.

Some snot in the back mentioned that under geometric tolerancing, the
tolerances were not cumulative. My response: that's true but you better
have better inspection folk and way more training because they are going
to reject the parts.



Harold