Despite all the precision in tool production, radius milling cutters in particular do not have a uniform geometry. The radius of each individual tool usually deviates individually from the ideal circular shape. Studies show that deviations of up to 0.015 mm can be expected with standard tools. Even high-quality, expensive precision milling cutters can exhibit deviations in the µm range.

This is a shortcoming for high-precision machining, as the contact point of the cutter radius with the workpiece calculated by the control does not match the actual radius - and this is the case every time a new cutter is inserted. With the 3D-ToolComp option from Heidenhain and the Cycle 444 3D probes, these deviations can be compensated for quickly and easily. To determine the radius deviations of a milling cutter to be used, the user carries out a test machining operation with the tool on a test workpiece. He then measures the milled contour with a touch probe that was previously calibrated with the help of 3D-ToolComp. The Heidenhain TNC control immediately converts the deviations of the milled contour from the ideal contour determined in this way into radius deviations on the tool and writes them into a compensation value table. This compensation value table can be used to define angle-dependent delta values that describe the deviation of the tool from the ideal circular shape. During subsequent full machining, the TNC control then corrects the radius value defined at the current point of contact between the tool and the workpiece.

The machining example of an aspherical lens with a diameter of 20 mm shows the effect of 3D-ToolComp very clearly. After the test cut, a touch probe with the 444 3D probing cycle detects considerable deviations of up to 25 µm from the desired lens shape. After compensating for the radius deviations, the shape deviations over the entire surface of the aspherical lens are less than 5 µm.

In order to be able to determine the contact point precisely, the NC program must be generated by the CAM system with surface standard blocks (LN blocks). In addition to the position of the tool, the contact point with the workpiece and optionally the tool orientation in relation to the workpiece surface are also defined in the surface standard blocks. The correction is carried out automatically by the TNC-controlled machine tool.

According to documents from Heidenhain