Choice Of The Calibration Sphere Position On The Machine Table; Notes On The Accuracy - HEIDENHAIN TNC 640 User Manual

Touch Probe Cycles: Automatic Kinematics Measurement | MEASURE KINEMATICS (Cycle 451, DIN/ISO:
G451, option)
Choice of the calibration sphere position on the
machine table
In principle, you can fix the calibration sphere to any accessible
position on the machine table and also on fixtures or workpieces.
The following factors should positively influence the result of
measurement:
On machine with rotary tables/tilting tables: Clamp the
calibrating ball as far as possible away from the center of
rotation.
On machines with very large traverse paths: Clamp the
calibration sphere as closely as possible to the position intended
for subsequent machining.

Notes on the accuracy

The geometrical and positioning errors of the machine influence
the measured values and therefore also the optimization of a rotary
axis. For this reason there will always be a certain amount of error.
If there were no geometrical and positioning errors, any values
measured by the cycle at any point on the machine at a certain
time would be exactly reproducible. The greater the geometrical
and positioning errors are, the greater is the dispersion of
measured results when you perform measurements at different
positions.
The dispersion of results recorded by the TNC in the measuring log
is a measure of the machine's static tilting accuracy. However, the
measuring circle radius and the number and position of measuring
points have to be included in the evaluation of accuracy. One
measuring point alone is not enough to calculate dispersion. For
only one point, the result of the calculation is the spatial error of
that measuring point.
If several rotary axes are moved simultaneously, their error values
are combined. In the worst case they are added together.
If your machine is equipped with a controlled spindle,
you should activate the angle tracking in the touch probe
table (TRACK column). This generally increases the
accuracy of measurements with a 3-D touch probe.
If required, deactivate the lock on the rotary axes for
the duration of the calibration. Otherwise it may falsify
the results of measurement. The machine tool manual
provides further information.
HEIDENHAIN | User's manual for cycle programming | 10/2017
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