On 1/2/2013 7:26 PM, Jim Wilkins wrote:
"Tom Gardner" Mars@Tacks wrote in message
...
I was always taught (while working toward my masters in Mechanical
Engineering) that the closer the tolerances the poorer the design.

I may have found the history of the 0.030" tolerance. A WW2 aircraft
sheet metal book I have shows sample prints for minor interior
sheet-metal brackets from Douglas Aircraft on which the default
tolerance for fractional dimensions is 1/32". The default for decimals
is 0.010" unless otherwise specified in the form of max over min, such
as 0.147 over 0.140 for clearance for the wood screws that secure cork
rings onto a thermos bottle holder.
jsw



Exactly. For most die work we'll hold .0005", for the length of the
pins on a die set we use a tape measure. The point is to know the
difference...and obviously the trolls don't.