Process and arrangement for the measurement of taper threads on a coordinate measurement device

A process for measuring taper threads on a coordinate measurement device which is outfitted with a table adjustable in the X, Y and Z coordinates for receiving a specimen provided with the taper thread and which further comprises a feeler probe which is held at a spring clip such that its position is adjustable in the Z direction and which is connected by this spring clip with a measurement sleeve which is adjustable in the X direction and at which is arranged a sensing element which can be deflected in the X coordinate, wherein a calibration of the feeler probe is initially carried out with reference to a setting gage, wherein, after calibration, the sensing element is brought into contact with different thread flanks one after the other for the purpose of measuring the taper thread, the measurement values determined in this way are stored in an evaluating unit and the characteristic values and fundamental quantities of the taper thread are calculated on the basis of the stored measurement values, comprising the steps of:

• initially taring the spring clip in a first step following the calibration in such a way that two coincidence marks which are associated with the Z coordinate, wherein one coincidence mark is arranged so as to be movable with the spring clip in the Z coordinate and the other coincidence mark is arranged so as to be stationary, are offset relative to one another in the Z direction, wherein the distance between the movable coincidence mark and the table support surface is less than the distance between the stationary coincidence mark and the table support surface;
• in a second step, defining a reference plane by adjusting the table in the Z direction until the table support surface contacts the sensing element and the table, carrying the sensing element along with it, is advanced further in the Z direction until the two coincidence marks coincide, and the Z value of the table position which has accordingly been reached is stored as a reference valve zA or the Z position that has been reached is set at 0;
• in a third step, arranging the specimen on the table support surface and carrying out the sensing of a thread turn by displacement of the measurement sleeve in the X direction, the sensing element being adjusted to the reversal point at the specimen circumference by displacing the table in the Y direction, and the coincidence marks are subsequently made to coincide on the spring clip by adjusting the table in the Z direction;
• in a fourth step, displacing the measurement sleeve further in the X direction until the sensing element has reached its zero position and, in this position, a first value pair x1, z1 is read off and stored, wherein x1 is the display value at the measurement sleeve and z1 is the table position in the Z coordinate;
• in a fifth step, sensing another thread turn on the same diameter side of the taper thread and similarly reading off and storing a second pair of values x2, z2;
• in a sixth step, further obtaining value pairs x3, z3 and x4, z4 from the diametrically opposite diameter side;
• and,
• finally, in a seventh step, determining the flank diameters of the taper thread and the taper angle error by the evaluating unit from the geometric relationships of the value pairs x1, z1 to x4, z4, wherein the feeler constant and the contact ratios of the sensing element in the thread are to be taken into account.