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Mechanical Edge Finder, should it be lubricated?


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Ian P14/11/2019 20:20:48
2379 forum posts
100 photos

I bought one of the Arc Eurotrade edge finders a couple of years ago and apart from a quick test when it first arrived I have never really used it. Today I experimented again but am not convinced it is any more repeatable than my goto method (short length of 4mm precision ground rod and observing light between it and the edge).

I then started to think about what the physics/principles of its operation were. I know the basic idea but how much does friction between the job and the (moving surface) compared with friction between the two faces of the finder affect its operation?

Other factors that might come into play are, the outer diameter of the two abutting faces and the diameter of the operating tip (on this Arc one there is a 4mm tip which is about 40mm lower than the split diameter bit). There is sticky grease between the moving faces but I dont know if that is meant to be removed or not.

Edge Finders

I know lots of people use these without problems (presumably) so maybe I am missing something.

Ian P

pgk pgk14/11/2019 20:29:49
1781 forum posts
287 photos

You should be able to wiggle it side to side without much effort but if it's got sticky with packing grease or old crud then I'd clean it out. As you know the function is simply to be pushed off-centre as it touches the edge and you don't want anything sticky stopping it. I don't think I've ever oiled mine but lucky my shed doesn't promote rusting.

Rather than squinting (and if you don't trust the edge finder) then a simple rod with a bearing and a spot of paint will work.


Phil P14/11/2019 20:48:46
627 forum posts
166 photos

I will also say that the bearing on a rod is a good solution, it is certainly the one I use 95% of the time on my Boley & Leinen (BCA) jig borer.

These are what I have custom made for my my machine and it is the one on the right with the 1/2" diameter ball race that gets used all the time.

boley 005 03-09-13.jpg

I also have similar ones mounted on plain round shanks that I use in collets on my Alexander milling machine.

I can usually rely on getting within .0005" using this type of edge finder and for most jobs that is more than acceptable. I have a few other ways of getting better accuracy, but this thing is just so easy to use along with the DRO.

Very easy to make and use, all you do is just move it until the outer race touches the work and stops spinning, that is where the spot of paint on the edge of the outer race comes in handy so you can see when it stops spinning easily. Then subtract half the bearing diameter to get your spindle centreline over the work edge.



Edited By Phil P on 14/11/2019 20:53:54

Edited By Phil P on 14/11/2019 20:54:13

pgk pgk14/11/2019 20:51:34
1781 forum posts
287 photos

Edited By pgk pgk on 14/11/2019 20:52:22

mark costello 115/11/2019 19:49:46
589 forum posts
12 photos

Years ago My edge finder got sticky. I called Starrett and asked what They used to lube Them with. They said STP. Don't know the British equivalent. Did not want to buy an entire can for just a couple of drops, so I started watching the skips around car auto parts shop and found a discarded can with an ounce or two in it. Still have it, still good after about 30 years.

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