# Accurate Edge Finding ??



## Philipintexas (May 14, 2015)

I have 2 mechanical edge finders, one .500 Diameter and the other with a .200 head diameter. I was told to bring the Edge finder toward the material at high spindle speed, it will form a perfect cylinder, continue until the concentricity of the shaft & head break. At that point you've found the edge. continue in half the diameter of the head and you have the spindle-axis on the edge of the material....

Sometimes I don't seem to be exactly right. 
1. How accurate should I expect a mechanical edge finder to be?
2. If I move till the concentricity breaks, haven't I gone slightly beyond the edge?
3. If so, do I compensate a fixed amount?

As with other simple gadgets, technique is everything, am I doing it wrong?


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## Swifty (May 14, 2015)

I have used a .200" dia edge finder for years, if I recall correctly, the idea speed is about 900 rpm, but I do tend to go about 1200. Your method is correct, as soon as it throws out zero everything and move over half diameter. If you are doubtful about accuracy, just check a couple of times to see if you get the same reading. There should be no need to compensate for anything, just make sure that you approach slowly.

Paul.


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## ownthesky2010 (May 14, 2015)

Spot on. I use one of these on my cnc mill and I get 0.01mm repeatability. Good enough for me. 
When I need to find the centre of a bore I always compare the y axis and x axis readouts and any difference is always measurable ovality in the bore and not error from the edge finder.


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## bazmak (May 14, 2015)

I have never used one but have ordered a cheap one from china
electronic beap type will soon find out if its useful


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## Metal_slicer (May 14, 2015)

I have a starrett .2" edge finder and I also have wondered the exact same thing. Sometimes the edge finder will jump offset quite a bit and other times it will jump offset a very tiny amount. I have never tested the accuracy but it seems to work well enough for the work that I have been doing.


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## nemoc (May 14, 2015)

Your technique is correct,  but I usually advance too quickly which can introduce error.  So I back off after it 1st indicates and advance again to within .003 or so and then move very slow until it indicates.  If you get inconsistent results check to make sure there are no burs on the edge of your stock.  You should get very accurate and consistent results.


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## toolznthings (May 14, 2015)

Metal_slicer said:


> I have a starrett .2" edge finder and I also have wondered the exact same thing. Sometimes the edge finder will jump offset quite a bit and other times it will jump offset a very tiny amount. I have never tested the accuracy but it seems to work well enough for the work that I have been doing.



  Take a look at my post in tips & tricks about edge finders getting magnetized.
Could be your problem.


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## Swifty (May 15, 2015)

Here's the style that I have, http://www.amazon.com/dp/B002SG7PPC/?tag=skimlinks_replacement-20. Occasionally I lubricate the mating faces with a bit of WD40, I have found that if they get sticky, they don't work as well.

I also have the type with interchangeable tips, but only use it occasionally in awkward situations.

Paul.


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## deverett (May 15, 2015)

The cylindrical type seem very popular these days, but GHT back in the 70's described in Model Engineer the manufacture of a similar type of device but using a 'ball on on a stick'.

Works OK for me and can get into places that the cylindrical type can't reach (such as the edges of large diameter cylinders).

Dave
The Emerald Isle


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## Blogwitch (May 15, 2015)

To put it bluntly, the best ones of these are the Starret range. I have been using both the imperial and metric ones for many many years. I have tried all of the others, but none come close. This really is a time when spending the money in the right place gives the best results.

Another point, you are using them way too fast to get accurate results. At 100 rpm, I can easily get within a few tenths (double checked with my DRO's and touching on with a cutter). You bring the tip in, and as soon as you detect ANY sideways movement, that is your setting, if it displaces any further, you are way out. The face you are detecting on should also be as smooth as possible, looking like a freshly sawn piece will be no good at all.

Where a lot of people go wrong is that the units do need to have correct lubrication between the sliding faces. It might seem a little gross, but I use a trick from my photographic days when reassembling cameras, I use nose grease. Just rub your finger down the side of your nostril, outside, not on the inside, that is called picking your nose. The grease that is picked up on your fingertip and gently applied to the sliding faces is enough to keep the sliding surfaces perfectly lubricated. Any more and you will have the tips sliding about all over the place, giving wrong readings.

This really is a genuine posting, picked up from many years of using these sensors.

I hope it helps.

John


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## Blogwitch (May 15, 2015)

Dave,
They are the 'wobbler' type, and as you have said, they are good for getting into tight places, especially down into narrow slots.

Where people go wrong with that type is that they play around with the socket holder and it can soon become unuseable.

I too occasionally use my Starret version to very good effect.

John


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## Swifty (May 15, 2015)

John, with all due respect, I know that you are happy with running your edge finder at 100rpm, but that speed is way too slow. A quick google search of edge finder speeds always says around 1000rpm, similar to what I have been using since 1970. With the Wobbler type that uses a ball socket, a far slower speed is needed. Next time I have the mill on, I will certainly try using 100rpm and compare the reading to a faster speed.

Paul.


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## canadianhorsepower (May 15, 2015)

I personally dont like using those:hDe:
so I got my self a co-axe centering tool
works great specially when putting something offset
in a four jaw chuck

cheers
Luc


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## Gedeon Spilett (May 15, 2015)

Not easy to compare, but the feel is the same type that is experienced with the micrometer.
the frictional force required to move the head of the edge finder should be comparable to that which one feels by measuring a piece between the micrometer rods to expect a similar precision. the optimal speed of the mill may perhaps depends on the stiffness of the spring, I also use it at 1000 rpm, this is really a great tool. 
I


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## mcostello (May 15, 2015)

I called Starrett years ago to find out what lube to use on their edgefinder. They recommended STP.


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## purpleknif (May 15, 2015)

m Not to be a smart alek but... If you need a dead accurate pickup you need to use an indicator and a flat block and swing the indicator both ways. I've been doing this for 30 years and this method will get you within .ooo1" when necessary.


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## RonGinger (May 15, 2015)

purpleknif, can you explain this a bit more- I don't see how you use a flat block and indicator.


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## BaronJ (May 15, 2015)

toolznthings said:


> Take a look at my post in tips & tricks about edge finders getting magnetized.
> Could be your problem.



I made my own and after several months it started acting oddly !  I discovered that mine was sticking due to becoming magnetised.

However a few moments inside the stator of a small motor with the rotor removed soon sorted it.

WARNING: If you try this,  the coil gets hot very quickly, so you only need to apply power for 20 or 30 seconds.  Which is more than enough time to demagnetise whatever you insert into the stator.


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## purpleknif (May 15, 2015)

RonGinger said:


> purpleknif, can you explain this a bit more- I don't see how you use a flat block and indicator.



 Hard to explain but I'll try. 1st you need to center your indicator. This is why most machinists use Interapid indicators because the stem is on center.  Set the ind. so that when rotated the lowest reading is zero when against the edge of the workpiece, In a vertical situation raise the ind to clear the piece and put a flat piece ( I usually use a TNMG insert ) Against the same edge of the workpiece. Rotate the ind and check the reading and adjust accordingly.
  I'm a PC moron but if you need more I'll see if I can get some help to post a few pics. 
  After 30some years you find there are some really creative ways to make pickups but this is pretty much the standard way to pick up an edge.


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## Swifty (May 15, 2015)

I carried out some tests this morning using the edge finder. I used a ground parallel held in the vice as my test piece, first off I used my normal method of running it just under 1200rpm, I tried several times and the largest difference that I got was .0002", more than good enough for me. Next I ran it at 100rpm, straight away I found that I had to approach at a snails pace, as it was slow to react when it found the edge, I had cleaned and lubricated the join beforehand, the largest difference that I got was .0006". Next, using the zero that I had when running it at 1200rpm, I used an indicator to actually check the the centre was on the edge, I couldn't see any difference in the reading of the indicator.

Of course, there are always a few ways of doing things to get the same result, no one is completely right or wrong. In my case, I'm more than happy with the method that I use, I can only suggest that members try different methods until they are happy with the one chosen. 

I have to correct myself in a comment I made in an earlier post, although I started work in 1970, edge finders of this type were not used, I assume that they were commonplace later in the 70's.

Paul.


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## Metal_slicer (May 15, 2015)

Swifty said:


> I started work in 1970, edge finders of this type were not used, I assume that they were commonplace later in the 70's.
> 
> Paul.



I am just a kid then at age 46 and a half. 

My .2" Starrett edge finder does not kick out well usually in one of the x or y axis. I can't remember which one. So it will kick out fine on one axis and half as much on  another axis. Regarding magnetism, can this condition occur if using only aluminum?


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## petertha (May 15, 2015)

Been really happy with my Borite
- accurate & repeatable to 0.0005" (limits of my DRO)
- at 35$, its priced similar to a good mechanical & 1/3 the cost of other electronic/bulb ones for some reason
- 0.375" ground shank so fits collets or most drill chucks
- 0.200" straight cylinder gets inside holes & easy 0.100" +/- compensate
- have not had any issues on any metal, bulb is bright on contact, still using same battery after 3 years
- no mill power required
- only downside is work must be conductive, so keep your mechanical spinners for that

I went through a few mechanical clones & they varied in quality. The comment about flat slippery surface between the shank & displacement disk segment is correct, at least that's how I 'fixed' one of them. The other potential issue is variable & crappy springs. A Starrett or Mitutoyo is probably better but just a guess, I don't have them.


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## RichD (May 16, 2015)

Maybe if I had an edge finder I'd use it, but what I usually do is put the mill spindle in neutral and rotate the cutter slowly by hand until I can feel the slight contact, then do my math from there as per the tool radius.
Rich


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## Cogsy (May 16, 2015)

I recommend you get one. I used to use that method as well, but it can easily put a mark on your work when you don't want it to, especially if you've already finish the O.D. I've never noticed a mark from an edge finder. I also use a coax indicator for centering round stock on the mill, especially centering on holes.


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## RonGinger (May 16, 2015)

Thanks purleknif, I think I get it. I always have trouble with rotating an indicator- trying to follow it when the dial is facing away from the machine and then confusing which side of the zero I am on. I once saw an indicator that had half its dial red and half green. For center finding I made an indicator holder that positions the dial so it is face up and its pin turned down 90 degrees. Much easier to use that way.


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## Blogwitch (May 16, 2015)

As you said Paul, use what you feel happy with, and I will stick to my method as it really does give me a much tighter tolerance.

John


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## GailInNM (May 16, 2015)

RonGinger said:


> ..... I always have trouble with rotating an indicator- trying to follow it when the dial is facing away from the machine and then confusing which side of the zero I am on.....



A simple little trick I learned a long time ago is to rotate the indicator dial so zero is at 3 or 9 o'clock instead of the more normal 12 o'clock. That way there is no mental confusion about which way is what as up and down don't change when rotating or using a mirror.
Gail in NM


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## purpleknif (May 16, 2015)

RonGinger said:


> Thanks purleknif, I think I get it. I always have trouble with rotating an indicator- trying to follow it when the dial is facing away from the machine and then confusing which side of the zero I am on. I once saw an indicator that had half its dial red and half green. For center finding I made an indicator holder that positions the dial so it is face up and its pin turned down 90 degrees. Much easier to use that way.


 
  Interapid indicators have a black line on one side and none on the other. There is no 'Reverse" on them because they swing both ways and have a friction clutch so you can use them in a lot of different positions. Plus the stem on the end is on center for easier pickups. I wouln't use anything else. I saw L.M.S. had "Interapid style" indicators at one time for around $80. Get one and you'll wonder how you ever lived without it !


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## Philipintexas (May 16, 2015)

I'm in the middle of a project and read all the suggestions. I think my technique is OK. I didn't state it before, but the purpose of my finding an edge accurately is so I can then find the center of some 3/4" stock for drilling.  Now comes the part where I have to admit being a dummy.

The center of 3/4" is .375...., unless the stock is really .7555!  :wall:


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## xpylonracer (May 16, 2015)

The mechanical edgefinder is certainly the low cost option and is capable of excellent results. In the past I have used the mechanical type but for the past 3 or so years have been using a PEC electronic edgefinder, red diodes light and show through the holes around the end when contact is made, I run at around 1000rpm on the spindle but have to approach the work with great care as there is no means of overtravel built in to the edgefinder, however used with care consistently excellent results are achieved.
Rgds, Emgee


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## poway_bob (May 16, 2015)

I have the PEC Electronic one. It clearly says NOT to run the spindle.

Bob


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## canadianhorsepower (May 16, 2015)

for those that are looking for something different
and useful for other thing then finding the center
of a hole. This is a great program, cheap but extremely 
hard to find on the internet. It does work with Window 7 32/64 bits
enjoy

Luc

http://miketreth.mistral.co.uk/centrecam.htm

I purchased an 8meg camera with LED from factory


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## Swifty (May 16, 2015)

poway_bob said:


> I have the PEC Electronic one. It clearly says NOT to run the spindle.
> 
> Bob



I've never used an electronic one, but what happens if it's held in a chuck and not quite running true, it won't be correct. With the mechanical ones, even if it's not running true it still finds the edge correctly.

For finding the centre of stock, if you have a readout, I touch the first side, zero the readout, then touch the other side and press the half button. But no readout means carefully measuring the part, and moving in from one edge.

Paul.


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## xpylonracer (May 16, 2015)

You are correct Bob but I prefer to have the spindle running as I find more consistent setting is achieved, maybe this is because when rotating a better electrical contact is achieved with the part.
Rgds, Emgee


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## petertha (May 16, 2015)

Swifty said:


> but what happens if it's held in a chuck and not quite running true, it won't be correct. With the mechanical ones, even if it's not running true it still finds the edge correctly..


 
True. But this scenario will be sub-optimal in any event. If your chuck is out by 0.002", you overcome this with a rotating edge finder vs. static to determine exact zero datum, now insert a perfectly straight spotter or bit into the chuck, now IT runs out by the same 0.002"  I suppose collets are probably better way to hold edge finders, but guess it all depends on what you have & what you're doing.

One thing I've noticed is they are all quite sensitive to edge surface condition. I've been tricked by the slightest amount of machining burr or finish irregularity.


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## redhunter350 (May 17, 2015)

Hi I Have not read every post so hope I am not repeating someone else, apologies if I do. In the late 60's and 70's I worked for quite a while on jig borers, typical tolerance +\ - 0.0002" max was probably 0.0005" occasionally a little wider on production stuff.

However one method of edge finding was to use a 1.00" bar in the spindle and 0.500" slip gauge between the bar and the work edge thus when set your spindle was precisly 1.00" from the edge. Believe me it is a VERY accurate method but you do need a good "feel" for the process.

Don't have a jig borer but I still use this method by putting a ground dowel pin in the EX collet, I use a 0.500" pin and a 0.750" slip, it is not as accurate as the jig borer but well within the capabilities of my mill ( either and Emco FB2 or a Bridgport)

Hope this helps
John (over the pond !)


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## Charles Lamont (May 17, 2015)

I have several methods. Until recently I had no milling machine, so all milling was done on the lathe using a vertical slide. In the lathe, the first method is a really accurate 1/4" piece of steel that came out of a dead VHS recorder ages ago. I use this in conjunction with a feeler gauge. Second is a cheapish alloy-bodied LED type, as per _expylonracer_. Both of these are used stationary, but need to be set to run true, and I have the advantage of having a Griptru chuck for the lathe which can be adjusted to about 1/4 thou. The body and probe of the LED indicator are not concentric so it has to be reset every time in is used. A quick dodge, rather than adjusting the chuck is to clock the probe and then turn the spindle to the position where the clock is reading in the middle of the range of runout. I would like one of the posh steel-bodied LED probes, like _petertha_'s (should anyone wish to give me one).

Since getting a milling machine last year, I have bought one of the Starret indicators, and that is what I usually use in the mill. The mill has 0.2" pitch feedscews, so I find the edge and adjust the dial to 100, taking several tries to get it spot on. This means the dial is on zero when the spindle is on the actual edge, which helps to avoid errors.

I occasionally use the ancient trick, when working directly from the tool, of using a cigarette paper to indicate the tool's arrival at the workpiece.


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## SmithDoor (May 17, 2015)

Use a scope this will hold with in 0.0001" [0.0025mm]
The co-axe centering is less than 0.0005 [0.012mm]
The Wiggler will hold 0.0015" [0.004mm]
The electronic edgefinder on good day is around same as Wiggler 
Light spot / Laser has spot of light around 0.020" [0.025mm] 

Most of my work I use a Wiggler and only use the other as need. 

Dave


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## bobsymack (May 29, 2015)

Could you use a small bearing mounted on a shaft and bring it into contact with the work piece until the bearing just starts to turn and then half the bearing diameter to find the edge
Vince


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## pete (Jun 4, 2015)

The Herman Smitt? (sp) mechanical edge finders are superior to even the Starrett's. But the reason the cheap off shore edge finders don't work at all well is because of the surface finish between the face of the probe and the face of the spindle. It has to be a hardened and VERY highly ground and then a precision lapped surface on both the faces that touch. Any roughness at all on either face will create drag and you won't get a tool that kick's out every single time like it should. Even with the very best mechanical edge finders they still will get a bit sticky over time with drying oil. Gently and just slightly separating the faces and spraying them with a contact cleaner and then relubeing them with half a drop of something like Starrett instrument oil will restore a really good edge finder to like new operation.

Even tho I have a digital 3D taster, I still use other edge or face finding methods when it's required and those other methods can work better in some situations. I've tested myself against that Haimer digital unit, and using the old school .001 thou Zig-Zag cigarette rolling papers they will consistently get me within .0005 or sometimes even a bit less if I apply myself. That method does take a light touch, but it can work very well if your willing to practice a bit.

Pete


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