On a piece to be milled many feature's position is referenced from the edges of the piece, like bolt holes. By placing the edge finder into the spindle and advancing the table until contact is made, your DRO can be zeroed. Once the piece's position is set, the tool of choice can be installed, the table then moved to the referenced position and the appropriate work performed in the precisely correct place. This is just one of many similar uses. Steve
This topic was practically beaten to death in this forum not very long ago. Search for it. One contributor did sterling work reporting on the accuracy of his tests, etc.
I'll take a stab at it.
It is a go-no go feeler gauge.
When set up the central core is on a tipsy edge of movement.
So now when it is held a slightest touch will set it off.
One eases up to the edge and it trips. Now where is the spindle center.
The edge finder is held in center by the holder. Mill holders are best, chuck ok and almost as good if tightened using all three holes.
The trigger cylinder is say .125" in diameter. Taking half of this, we determine where the center really is since we touched the edge.
It is like a balance beam on a knife edge. Pushed latterly and the beam 'drops'.
Bob La Londe wrote:
Actually -- the two I have are 0.500" diameter and 0.200" diameter, with the latter easier to use with a resettable dial on the handwheel. Run to the point where it just trips (or just before it trips, depending on your need for precision), and then set the dial to indicate 0.100" (the radius of the finder's tip, and thus how far your center line is from the edge).
The 0.500" one is more of a pain, because you have to set the dial 0.250" off.
I presume that they are also made in metric units, in which chase perhaps a 6mm diameter would give you an offset of 3mm. A 20mm one would be nice for a dial which read 10mm full turn -- but would be rather too large for convenience. A 5mm would leave you working with half a mm.
An imperial one would be a real pain to use on a metric machine, and vice versa.
Anyone out there have a metric version? If so, what is its working diameter?
Martin sez: "It is like a balance beam on a knife edge. Pushed latterly and the beam 'drops'."
Very nice description, Martin. Hmmmnnn, never thought about it before but it makes me wonder; If a wiggler used horizontally, as in a lathe, would be less accurate because of the force of gravity added to its moment of inertia.