I'd like to talk about edge finders

[Nitsuj]

Since I don't have a mill, I've never used an edge finder, but I recently watched a video on their use. I learned something that doesn't make much sense to me.

Ok, let's say I have my edge finder mounted, the video I watched says you bring the work piece to the edge finder, until it turns true them keep moving the work until the edge finder pops out of true again.

Now, I would think that as you move the work into the finder, when it turns true, you're actually making contact. Once you advance until it pops out of true again, you've went past the edge. Again, this isnt from experience, just what I walks thought. I'm obviously wrong, and I can handle being wrong(I'm married) but I always like to know why I'm wrong. Any input?

[Mayhem]

I have been wondering about this as well, as I have seen some do as you describe whilst others do what (to me) makes more sense and stop once it runs true.

Having said that, I have read that if you do this you subtract the .001" that it takes to push it out of true when calculating the edge.

The other thing that strikes me as strange is edge finders that have a diameter of 3/8" (for example). You divide .375 by 2 which gives you .1875. Surely having an edge finder of .200 makes life easier?

[Tony Wells]

Many do have a 0.2000 diameter. And some have a 0.5000 diameter. In fact, I haven't seen one that the main contact diameter is 0.3750. I have a Starrett (or 3) with a 0.3750 body that has a 0.2000 contact diameter and a short section immediately above it that is 0.3750, and have used that part before, but it is a very short (around 1/8" I'd guess) and awkward to use.

The issue with stopping when it runs true is that you can't really see when it is. As you approach an edge with it "wobbling", yes it runs truer and truer as you get closer, but if you try to declare a perfectly true point with your eyes, you won't know whether you are right on the edge or maybe a few thousandths away. The physics behind it require the contact diameter to "pop" off to the side require very little overtravel. Probably in the 0.0002 range. That can be considered negligible for most work, and I suspect far closer than you could get by eye as you approach the edge and declare a true running edge finder.

[krv3000]

hi this is a old way of seting up on senter get a dawel say 6mm od put it in the mill and cote the dawel in marker pen bring the dawel to the work pece and tuch on the work pece once you see the ink bin rubed off stop the mill then if you have a dro set to 0 then remove 3mm and reset the dro to 0 the other metherd is to use cigeret papers dampen the edge of the work pece and place a pece of cigeret paper on it bring say a 10mm slot drill to the work pece wher the paper is and cerfuly bring the cuter to the work pece as soon as the cuter pics up the paper stop the paper is so meney microns thik deduced that with hafe the thiknes of the cuter then you is on center

[Bogstandard]

You are all jumping to the conclusion that it is thous between centred and off centre, when in fact, most edge finders, like the Starrett, comes off centre when it moves approximately 2/10ths (0.0002").

So in reality, it can be ignored.

Now where a lot of people go wrong is that they don't treat their edge finder as a precision instrument, which it is, and drop it anywhere that is available and never really look after it. Even using the wrong lubrication can cause it to mis-read.

If you suspect your edge finder isn't being too accurate, clean it off in some spirits and re-lube it with either watch or sewing machine oil, NOT the usual suspects, WD40 or 3 in 1 (they contain certain ingredients that gum everything up), and do it very liberally, one tiny spot on the sliding faces is plenty, and don't go pulling at the internal spring, just gently lift the sliding edges apart, enough to pop the oil in there. It should then work like a brand new one, like mine, and that is well over 20 years old.


John

[Highpower]

(04-18-2012, 03:33 AM)Bogstandard Wrote: You are all jumping to the conclusion that it is thous between centred and off centre, when in fact, most edge finders, like the Starrett, comes off centre when it moves approximately 2/10ths (0.0002").

So in reality, it can be ignored.

I have to go along with this based on what I have experienced.
The scales on my mill DRO have a resolution of 0.0002" and I find that I can "tickle" a (good) edge finder between centered and off set, by getting the last digit in the display to flicker the last "0". So it may actually come close to taking only 0.0001" to offset the the edge finder.

I've done this using an audible edge finder while closely watching the last digit on the display. I can hear the finder just start to tick as the DRO digit begins to flutter.

I think the material can make a difference as well. Aluminum or brass seems to "grab" the edge finder sooner than Iron / steel. Seems to be that way to me anyway....

[PixMan]

This. Use a quality Starrett, Fisher, Moore or other edge finder, rather than a $5 Chinese import. There's a world of difference, in price and performance. In the case of a Moore Tools one (no longer made), it's a universe of difference in price.

[Bogstandard]

I have both metric & imperial Starrett edge finders, plus also a couple of the the cheapo far eastern ones.

The far eastern ones work just as well as the more expensive ones if a little 'tweaking' is carried out.

Do as I did in my earlier post, a good clean out with a spirit based cleaner (no residue left behind), then a very light lubrication.

The far eastern ones usually come packed with grease or heavy oil, to help protect them during transit, and that needs to be removed from the sliding faces before use, otherwise they give all the wrong readings.


John