Another Edge Finder

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Winegrower

H-M Supporter - Gold Member
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Jul 29, 2014
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534
I normally use the cylindrical type of edge finder that kicks off center at some kind of fuzzy point. I have always been suspicious of this device, without evidence however. Every time i’ve checked for repeatability, it does ok, so I use it. If I did not have a DRO I am pretty sure I would not like the 0.100” offset compensation. And my eyeballs have to get closer to metal parts than I like.

But Joe Pie on Youtube showed a really clever device (see the photo). It has a 3/4” shank, and one face is exactly on the shank centerline.
The other three faces are exactly 0.500 away from center. This allows a few features, but mainly I like that you can move the work up to this, feel the self alignment, and get a good feeling that this is actually the edge. I made an attachment awhile ago for my vise that makes it easy to align on the fixed jaw with this tool, rotate it 90 degrees and pick up the x axis as well.

However, in the making of this, some inexplicable tragedy occurred and the main face was exactly 0.020 too deep. Rather than scrap and start over. I bored out and pressed in a 0.75” diameter plug and machined that off to the, this time, correct depth. Trying it out, I was either spot on with the rotary edge finder, or at most 0.001 off. I have more confidence in this new one I think.

The picture makes it look like a poor finish, but it is quite smooth really. Really.

Or, Joe sells them for around $40.
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chips&more

Active User
Registered
Joined
Mar 19, 2014
Messages
2,611
I have concerns about the feel technique? You a lot of mechanical advantage from handle to work. And lose the ability to have a sensitive touch and spring and all.
 

Winegrower

H-M Supporter - Gold Member
H-M Supporter Gold Member
Joined
Jul 29, 2014
Messages
534
A valid point, Chips. Of course it's feel and sight together. The work and the indicator visibly align as they approach the zero point and there is feedback through the handle, much like using a micrometer. Brute force would be a bad thing. I can easily feel contact and when it's too much force. Perhaps if you have eyesight like an eagle, which I have to say I don't, the rotating finder is more to your liking.
 

RJSakowski

H-M Supporter - Gold Member
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Feb 1, 2015
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4,612
If I recall correctly, the technique was to slowly approach the edge as you rocked the spindle back and forth, feeling for the play. When you can no longer detect movement, you have reached the edge. I use a similar procedure when fitting gage pins to holes. You can detect a .001" gap this way.
 

benmychree

John York
H-M Supporter Gold Member
Joined
Jun 7, 2013
Messages
3,981
The standard type of edge finder can be made more sensitive by grinding a small flat on it's diameter, it tends to make it "kick out" sooner than without a flat. Personally, I just position a strong light behind the part/edge finder and approach until I see no light at the interface. There are also edge and corner finders for high accuracy work that have a accurately ground hole and vertical face that you dial indicate, some have a magnet on the face to hold it on the workpiece, the corner finder has two magnets.
 
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