Several machine tools must be checked periodically for geometrical deviations. Possible changes of the geometrical characteristics of the machine tool have a direct influence on the quality of the work pieces manufactured.
A machine tool must be checked on possible geometrical deviations. The check must show up eventual rotations of the table during displacement.
The measurement of geometry should be made in a quick, reliable and simple procedure ant thus with a good cost benefit effect.
ENGINEERS SET, consisting of
(For measurement on machine tools usually instruments with a sensitivity of 5 μm/m are preferred)
On machine tools the most important point is, that during the displacement in one axis the tool will follow a straight path compared to the table. Mainly machines of light-weight construction show the tendency that the table can in the extreme positions suffer a certain amount of deformation due to its own weight or a rotation of the transversal guide way due to the weight of the table. Provided that the complete machine construction is tilting during the displacement of the table this is a sign for insufficient stability of the foundation or for a flexibility of the stand (damping elements).
For this purpose the reference instrument is placed on a stable position of the machine bedding, the measuring instrument is placed in the centre position of the table in the same direction. The two instruments are used in differential measuring mode and set „Zero“ (setting the difference = 0). The table is now displaced in defined steps and a possible angular difference is recorded. When an angular deviation is visible, this means a deformation of the table resp. a rotation of the transversal guide way is present.
The same method can be used for a variety of measurements, e.g. comparison of the table vs. the transversal guide way, angular changes during longitudinal or transversal moves compared to the spindle, etc.
An important point is the checking of right angularity between table and spindle axis. For this purpose usually a prismatic angular measuring base is used (if possible with magnetic inserts in the vertical base). The horizontal „Zero position absolute“ is determined by a reversal measurement on the table. After that the „vertical position absolute“ is determined by a reversal measurement on the spindle. The difference between the two measuring values absolute stands for the deviation from right angularity.