HEIDENHAIN ND 1400 - Manual (Page 67)

53
6
Measuring
Probing arcs
A minimum of three probed points is required to measure an arc. There
is no practical limit to the number of points that can be probed, and in
general accuracy is increased by probing more points.
When the arc is less than 185 degrees, Measure Magic will correctly
recognize the arc and assign the correct feature. However, when the
arc is 185 degrees or more, it is likely that Measure Magic will assign
the circle feature type to the data. If the arc is shallow, Measure Magic
might mistakenly assign a line feature. If the wrong feature type is
assigned, it can easily be changed by selecting the correct feature from
a menu of alternatives in the DRO screen.
A best fit algorithm is used to define the arc when more than three points are probed. The arc fit to the data
can also be changed by selecting the desired fitting algorithm from a menu in the DRO screen. Please refer
to Chapter 12: Reference Materials for details regarding the fitting algorithms.
Measurement results are shown in the Feature list, View screen and DRO screen. The DRO screen shows
the number of points used, the radius and diameter of the arc, the coordinate location of the center of the
arc, form error, reference frame and the projection plane. The feature graphic in the View screen shows
the feature and the points used to define it. Errors are shown as whiskers connecting the probed points
to the feature. The maximum errors are shown in red and are used in the calculation of form. When only
three points are probed, the form error is zero. When more than three points are probed, the form error is
the sum of the two greatest opposing error magnitudes.
In this example, three points are
probed to measure an arc
Touch the feature type... to display the menu of alternative
types
Probed points are shown in the
View window
Measuring Features