Edge finder
An edge finder ( engl . Wiggler or edge-finder ) is a setting device, which in the machining allows machining, the spindle of the machine tool with the rotation axis exactly on the edge of the workpiece to align. There are mechanical edge finders with an accuracy of about 0.005 mm and electronic ones with an accuracy of up to about 0.002 mm.
The mechanical edge finder is mounted on the spindle of a milling machine and consists of two offset cylinders that rest on the thicker diameter and are connected inside by a spring. Even at a low number of revolutions of the spindle, usually 600 rpm, an eccentricity of the lower cylinder to the axis of rotation of the upper cylinder clamped in the spindle occurs. When approaching the workpiece edge slowly, the axes of the two cylinders approach until they are almost centered. Then the button touches the edge. If the spindle is now moved by the cylinder radius, the spindle axis is exactly above the workpiece edge. If the edge finder comes too close, the lower cylinder visibly slides sideways.
Using the same principle, the center lines of bores can be determined with conically shaped probe heads .
Electronic edge finders either work in the same way and only show the coverage of the axes by an optical ( LED ) or acoustic signal, or the edge finder detects the edge of the workpiece by closing a circuit when touched. In the latter case, the calibration can be carried out with the spindle stationary and with greater accuracy. This measuring method cannot be used with plastics and wood, as these do not conduct electricity.