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How does an edge finder work?

Shop for Centre and Edge Finding Sets

An edge finder is mounted in a collet, end mill holder or drill chuck and secured to the spindle of your machine. When the spindle of the machine is rotating (at between 500 and 1000 RPM), the tool is able to very accurately locate the edge of a part (to within 0.15mm or 0.005 inches). An edge finder is mounted in a collet, end mill holder or drill chuck and secured to the spindle of your machine.

When the spindle of the machine is rotating (at between 500 and 1000 RPM), the tool is able to very accurately locate the edge of a part (to within 0.15mm or 0.005 inches).

The contact probe of the edge finder is secured to the shank by a tensioned spring inside the tool. The contact probe of the edge finder is secured to the shank by a tensioned spring inside the tool.
As the the edge finder moves towards the edge of a part, the spring starts to centre the tool until it runs true and appears not to move at all. As the the edge finder moves towards the edge of a part, the spring starts to centre the tool until it runs true and appears not to move at all.
Contact with the edge of a part pushes the tool off centre and the contact probe becomes offset from the shank. This indicates that the edge has been found. Contact with the edge of a part pushes the tool off centre and the contact probe becomes offset from the shank.

This indicates that the edge has been found.