Your Holes at any Angle!
I keep hearing folks say that the
primary datum used to control a hole must be at right angles
to the axis of the hole. Not true! Pick your datums based
usually on function. If some of the holes happen to be at an
angle other than 90°, so be it. As long as the BASIC linear
and angular dimensions used to locate the hole eventually get
back to the datum, no problem. In this example, the 8.5mm hole
is not perpendicular to any of the datums referenced. The
Ø0.4mm positional tolerance is located by the 20mm, 30mm and
45° BASIC dimensions.