What are edge finders and what types of edge finders are available?
Edge finders perform a similar function to dial test indicators (DTIs) during machine set-up, in that they are used to find the edge of a workpiece, component or stock. The key differentiator between the two measuring instruments is that edge finders will simply detect the presence of an edge (internal or external), whereas a DTI will show run out, discrepancies or the position of an object. Also, as the name suggests, a dial test indicator features a dial readout, whereas edge finders traditionally feature a LED light which illuminate or an audible beep when the edge is found.
Mechanical edge finders, also colloquially referred to as ‘wobblers’ are also available. Instead of using an LED light or beeper, the top part of the edge finder will spin off to the side when it reaches the edge. You would then set your machine to zero at this point. Each edge finder features either a ball or flat tip which will perform the operation made from a hardened material. 2D or 3D edge finders are available, with the ‘2’ or ‘3’ meaning the number of axis it can measure in. A 2D edge finder can measure in the X and Y axis, with the 3D edge finder measuring X, Y and Z axis.
How do you use edge finders?
To use an edge finder, you would mount it in the machine spindle (either a chuck or collet) and then slowly move the spindle inwards until the edge is reached. When the edge is found, a beep, LED illumination or ‘wobble’ will occur in response. This can be performed on either outside edges or internally in slots or bores.
When using an edge finder, the operator will need to perform some calculations to find the zero point of the edge of the workpiece. Using a ball tip, the general principle would be to add or subtract half the value of the diameter (or the radius, r) to find the zero point / machine spindle centre line. So, for instance, if you were edge finding two sides of a workpiece with a 5mm ball tip, you would find the edge on both sides and, when reaching the edge, you would calculate x-2.5 on one side and x+2.5 on the other (with x being the point at which the edge is found).