I was taught a new way to use an edgefinder today. What are your thoughts?

Just found this video by Tormach. It says that the difference between the edge finder running true and kicked offset is .0005. If that makes a difference, you shouldn't be using a mill or an edge finder.

 
Run the edge finder up until it just kicks sideways, set the dial on the mill to 100. Taught that way in school, confirmed by my first boss. I've never seen it done any other way.

Edit: I do back off after setting the dial and slowly crank up again to double check the setting.

X2
 
He's wrong. How does he know when the table is no longer touching the edge finder? It will continue to run true after it is no longer touching the part.
 
The edge finder has been my weapon of choice in finding an edge for more than thirty years. I usually make three approaches, the first rather quickly to get a rough idea of where the edge is and then advancing about .0001" every 1/2 second in the last 1 to 2 thousandths, repeating the procedure until I can locate an edge to .0001".

Approaching too rapidly will give a false position, either due to overshoot or if there is a small amount of wobble, kicking out prematurely. It has been my experience that once the edge finder kicks out, you have to back away by several thousandths before the edge finder settles back to a stable mode.

I routinely use my finger nail to recenter the edge finder after backing out about a thousandth as this reduces the amount of travel for the next approach. If I don't use my fingernail to recenter the edge finder, I have to back it out about 6 thousandths before it resets, at which point, there is a clear air gap between the edge finder and the work.
 
He's wrong. How does he know when the table is no longer touching the edge finder? It will continue to run true after it is no longer touching the part.
He is saying that the difference between the centered edge finder and being kicked out is .0005", not going from offset to centered again.

The edge finder of this type was patented by Robert Beatty in 1948. (US Pat. 2451904) Among his claims was that when an edge is contacted by the centered finder, the additional travel to the point where the tip is displaced is never more than .0002". Starrett also makes this claim for their product.
 
Like everyone else, my Bridgeports were bought late in their lives and came with some "slop" in the screws. I have a DRO with glass scales to take the guess work out of everything I do. I use Fisher edge finders (not the ones that click) just about every time I set up a new part, be it picking up an edge on finding the mid point between the jaws of a part in the vise. I set the DRO when the edge finder kicks out, then I back off and do it again. 99.90% of the time it kicks out within .0002" of zero. I do the same thing when finding the mid point, I touch each jaw and look at the number on the DRO. They match the same percentage of the time. If I need real precision I'll pick up the edge with an indicator.
I learned long ago to recheck the positions before I cut metal, even if the location isn't that important. When I screw up, I screw up big time.
 
The great thing about an edge finder is that it is insensitive to runout. The tip centers on the spindle axis. Electronic edge finders, probes and Haimer tasters all have to be zeroed to the spindle axis to read accurately. As such, the orientation of the device in the spindle has to be strictly observed in order to maintain alignment.

Finding the midpoint with an edgefinder and DRO is particularly satisfying as I find one edge, zero the DRO (don't worry about compensating for the edge finder diameter) and find the opposite edge. Then I hit [1/2] on my Grizzly DRO or enter "/2" and [ENTER] on my Tormach PathPilot display. Zero is set at the center of my part. Sweet!
 
he guy training me tells me I am doing it wrong and tells me to get out of the way so he can show me how its done.

Here's why he's very wrong:

Lets ignore DRO's altogether. I never saw one on a Bridgeport until about 16 years ago. A skilled operator will snug the table lock slightly when approaching zero to remove table slop and keep from overshooting a number. They will also approach a dimension by turning the handle in one direction only to keep the lead screw on one side of the nut. If they overshoot the number they'll back off a full revolution and re-approach to remove all backlash. Having the lock snugged also allows some tension between the interacting surfaces.

Backlash on a Bridgeport (dead space between the lead screw and the Bronze nut) is typically set around .025". If you change directions after your edgefinder kicks out, far enough to draw it back concentric you've not only removed all tension you set finding the edge, you're now on the wrong side of the nut (if you're lucky) and will need to use that same direction on you handle when moving to the next position. More than likely you're actually lost somewhere in the backlash.

So nothing ever changes. The dude is doing the Alpha Dog routine. Watch for wet spots in the corners of the shop. I chuckled about this on the long drive home tonight.
 
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