Accurate Edge Finding ??

[Metal_slicer]

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?

 

[petertha]

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.

 

[RichD]

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

 

[Cogsy]

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.

 

[RonGinger]

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.

 

[Blogwitch]

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

 

[GailInNM]

..... 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

 

[purpleknif]

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 !

 

[Philipintexas]

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:

 

[xpylonracer]

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

 

[poway_bob]

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

Bob

 

[canadianhorsepower]

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

 

[Swifty]

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.

 

[xpylonracer]

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

 

[petertha]

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.

 

[redhunter350]

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 !)

 

[Charles Lamont]

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.

 

[SmithDoor]

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

 

[bobsymack]

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

 

[pete]

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