Mill Work Holders - 3: The Edge Finder
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
After aligning the vise it is sometimes necessary to precisely locate a position on the vise or the work piece held by the vise. For this task an edge finder is available. An edgefinder is a precision instrument that assists the machinist in locating important features on the work piece. It consists of a shank and a floating tip. The edgefinder tip is precisely ground to a known diameter. In this case, .200 inch, but others are available.

The tip of the edgefinder is held to the shank with a tension spring and can move side to side. So that you will not damage the spring, do not use the edgefinder at a spindle speed higher than 1000 RPM .

Some important facts to know before continuing:

  • The edgefinder must be set eccentric while away from the work piece
  • The edgefinder tip becomes concentric as it is moved into the work piece.
  • The edgefinder moves quickly away from center when the edge has been located.

The edge finder can be used to locate the edge plane of a part with reasonable accuracy. The following procedure uses a DRO , but the same process can be performed with the micrometer dials on the table handles.

Setting longitudinal direction (X):

  • Using the table handle, slowly bring the edgefinder in contact with the work piece.
  • When the tip of the edgefinder moves just a bit off center it means that the center of the spindle is exactly one half the diameter of the edgefinder away from the edge of the part (.100).
  • Lower the table to clear the edgefinder from the work piece.
  • Set the DRO to zero in the X direction (or set the longitudinal micrometer to zero).
  • Move the table .100 - which is half of the edgefinder diameter - towards the interior of the part.
  • Again, reset the DRO to zero in the X direction (or set the longitudinal micrometer to zero again). The center of the edge-finder is now on top right edge of your part.

The same procedure can now be used to locate an edge in the cross direction (Y)

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