The Edge Finder

By Mike Rehmus


The Edge Finders and Wigglers we purchase are sometimes furnished without instructions and we are frequently uncertain of their proper application.

The Edge Finder is a dynamic indicator of the location of an edge with reference to the centerline of the longitudinal axis of the spindle to which it is attached.

In use, the spinning Edge Finder is moved into contact with the edge that you wish to locate. As the lower cylinder of the Edge Finder touches the edge, that lower cylinder 'kicks' to the left (assuming a clockwise rotation as seen from above)

When the kick is observed, the axis of the spindle and the edge of the workpiece are located 1/2 the diameter of the Edge Finder from each other. This is typically 0.100" (0.200/2 = 0.100") but can be different so check.

  1. Do not chuck the Edge Finder with excessive pressure. It is hollow and can be crushed.
  2. You should run the Edge Finder at about 1000 rpm.
  3. If possible, the spindle should be extended so that when you see the ‘kick’, you can retract the spindle and remove the Edge Finder from the workpiece. This saves wear and tear on the lapped surfaces of Edge Finder.
  4. View the workpiece/Edge Finder contact by aligning your eye behind the Edge Finder and at 90 degrees to the workpiece for maximum visibility of the ‘kick’.

  5. The working portion of the Edge Finder is the smaller diameter cylinder. This is the part that should contact the edge in questions.
  6. Oil the Edge Finder maybe once a year if you only use it occasionally. You may have to pull the cylinders just slightly apart to get the oil in between them. Be careful. If you distort the spring holding the pieces together, you will need a new Edge Finder.
  7. Make certain there are no burrs on the workpiece or you will get a false edge indication. The same goes for excessive oil on the workpiece.

    8. Cheap Edge Finders are probably not worth the effort to take them home. A Starrett does not cost a lot of money and the difference in accuracy and ‘action’ between a cheap unit and a Starrett is noticeable.


Email: Mike Rehmus

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Rev. 12/04/96