- [Instructor] For simple surfaces,
geometric tolerances can sometimes be evaluated
with a dial indicator.
For example, the flatness of a surface can be indicated
by mounting a dial indicator above a surface plate,
and moving it parallel
to what the perfect surface should be,
while the part is held fixtured to that surface plate.
This technique can prove difficult for more complex parts,
so other methods should be considered.
One of the most direct methods
to verify the tolerance of a part,
is through the fabrication and use
of a go gauge, or a no-go gauge.
The go or no-go gauge
is designed to mate with the manufactured part.
Any feature of the manufactured part
that is outside of the specified tolerance zone,
will prevent mating with the gauge.
The gauge must be fabricated more precisely
then the part being evaluated.
Typically, gauge tolerances will be 10% of the tolerance
given for the manufactured part being evaluated.
Another common method
for verifying the geometry of a manufactured part,
is the use of a coordinate-measuring machine.
These ultra-high-precision devices
are mounted on a rigid base, and have an articulated arm,
with a probe tip attached to the end.
The probe tip can be moved around in space,
and the location of the probe tip is recorded.
The part needing to be measured is mounted on a rigid base
near the coordinate-measuring machine.
The probe tip is moved around the surface of the part,
and the coordinates of the probe tip are recorded.
This set of points are compared
against the ideal geometry of the part.
Any point coordinate
which is outside of the desired geometry,
more then the tolerance specification allows,
will cause the part to be rejected.