Chapter 3 Operation
3-32
DatumDatum
DatumDatum
Datum
All measurements are relative to a datum. A datum is the zero point or origin of
the coordinate system. Establish a datum once the part is skewed. The simplest
way to establish a datum is to zero the X and Y axes on a point. In the example
below, the skew line and a second line are used to construct a point. Both axes (X
and Y) are zeroed on that point which then becomes the datum. Datum points
can be constructed from the center point of a circle or any other construction that
produces a point. Generally the datum, or the features used to construct the
datum, are called out on a part drawing.
The QC200 allows users to construct two reference datums for measurements.
Datum 1 is the original datum and datum 2 is a temporary reference frame useful
for incremental measurements. Use datum 2 for incremental measurement while
maintaining the position of datum 1. For example, obtain the incremental dis-
tance (X axis travel) of a series of features. Probe a point on the first feature and
establish it as datum 2. Place the crosshairs on the next feature in the series and
measure a point. The X axis displays the distance from the first feature to the
second. Now establish datum 2 on the point on the second feature. Place the
crosshairs on the third feature and measure a point. The X axis now displays the
distance from the second feature to the third. Continue in this fashion until the
entire series measured.
To construct a datum
Steps 1 through 3 measure a second line. This line and the skew line will be used
to construct a point.
Step 1
Press the line key.
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