Metal-cutting or machining processes are the preferred means of fabricating metal workpieces. Constantly increasing demands regarding precision, service life and machining speed have created a need for increased accuracy in the measurement of tool geometry. This is especially the case where specific dimensions of tools directly influence the form of the parts to be manufactured (for example, the diameter of drill bits and reamers, the thread shape of screw taps or the overall contour of profile cutters). In this connection, it is important to make a distinction between tool presetting and tool measurement. These two tasks involve different accuracy requirements which can be met only by system solutions that differ accordingly.

During presetting, the position of certain tool features is measured relative to the tool holding fixture. This information is used to align the cutting tool in the machine tool or machining center. Since deviations with a magnitude of several micrometers usually cause no problems, devices for presetting tools generally have a relatively low measuring accuracy. They are custom-designed for users of metal cutting tools in production.

Both the tool manufacturer and the user’s incoming inspection department must ensure that the tools meet their geometric requirements. High-precision measuring machines are also required to check this with sufficient accuracy. Tool dimension accuracies of only several micrometers, and sometime even in the submicrometer range, must also be detected in order to generate the correction values required for the manufacture of tools. The accuracy of tool presetting equipment is not sufficient for such precise workpiece measurement. For this reason, coordinate measuring machines with air bearing technology are used. The function-determining cutting edges of the metal-cutting tools can readily be measured using image processing sensors in conjunction with a rotational axis. They are screwed into the axial cutting plane and the high-precision measurement is performed in this position. Other sensors are required to measure free-form surfaces, clearance angles, or the geometry of drill bit tips. One possibility is the use of contact styli. However, since their probing elements are relatively large, it is difficult to measure small tools using styli of this type. The Werth Fiber Probe is very suitable for high-precision measuring tasks, and entire free-form surfaces can be measured using the 3D-Patch software.

The generation of program runs for tool measurement frequently represents a problem. Many tool measurements require extremely fast results. This requirement can be met with parameter programs, for example, general program runs created for entire classes of repetitive feature step drills, twist drills, screw taps and hob cutters). For example, a measuring program for a generic hob cutter compliant with the German standard DIN 3968 is stored in the parameter program for hob cutters. The operator can measure a variety of hob cutters ranging from a simple rack hob to a worm wheel hob by selecting the article number or the individual tool parameters (Fig. 61).