Edge finder use essential?

[jon hill 3Participant @jonhill3]

Having watched a few blondie hacks videos on using the mill she often uses an ‘edge finder’ however I have never used one and don’t have a DRO.  So do I need one and how do you make the best use of it?

[Brian WoodParticipant @brianwood45127]

Hello Jon,

I don’t always use one. For simple work locating the centre of the job can be done with a conical feature such as a morse taper centre, or the conical taper surface of a drill chuck for larger diameter holes. Just push it into the hole and move the job about until it fills the hole all round.

For finding edges, a magnetic feeler gauge, nudged over by the tip of the centre will do for undemanding work, but for non magnetic jobs that won’t work and the centreing tool becomes the go-to option. A DRO also makes the use of that arrangement so much more convenient as you can set the start of the dimension when you see it ” break” and repeat that on the other side to leave you with halving the distance between the two DRO readings

I suggest you do a bit of reading as well.

Regards   Brian

[Nigel Graham 2Participant @nigelgraham2]

Yes! Or very nearly so.

Further, far more than a DRO!

The electronics are good to have but they perform a different function. DRO or plain dials, you still need to identify the datum sides from which other dimensions spring. That’s what the edge-finder is for. You can use alternative methods I describe briefly below, but it certainly does help you.

I don’t know the type Blondihacks uses, so perhaps it’s one designed for use with a DRO.

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You need locate a hole, width or other feature more often from an edge than anything else. Often the work-piece is essentially rectangular and then one corner acts as the datum for the rest by being two edges at right-angles. That corner should be as shown by the dimensions on the drawing – if you have a drawing and it’s dimensioned properly!

Best use? Well, really it can only be used for its one purpose and in one way.

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I’ll describe as for a milling-machine with no DRO but the instructions are the same.

The plain types are commonly a probe mounted in the end of a cylinder containing a spring that acts on the probe. The cylinder is set in a chuck or collet, and that set revolving at a modest speed.

The table is advanced to bring the edge, strictly, the vertical face below that edge, moved slowly into contact. Keep going, gently: the probe moves into concentricity with the spindle, until just as it goes past centre it suddenly flicks far out of concentricity. One type swings the probe up away from the edge, another keep it against the face but obviously eccentrically to the axis.

That places the edge (which can be something like a vice face, not necessarily the work-piece) short of the spindle axis by the probe radius.

Then move the table further in by that radius, to put that datum edge directly below the axis.

Null the dial (or the DRO reading) for that direction.

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It’s good practice to wind the table well back and try again, to verify the first reading. I usually manage to make the two readings within a couple of “thou” or so of each other, so I set the table to the average point, then test again.

NB: always approach from the same direction to remove backlash errors..

….

If setting a datum corner you now move the table so the first “edge” is past the spindle and repeat the above for the second edge, at right-angles.

Depending on the work itself, if you are trying to locate features on a centre-line symmetrically between parallel sides, some advise testing off both opposite sides.

”””

Are there times when the edge-finder, or lack thereof, is not critical?

Yes.

You can locate the edge under the spindle axis by using a cutter. The work is advanced towards the revolving cutter until its flank edges just start to tear a piece of thin paper “glued” to the work side with a touch of oil. Then with the cutter retracted, advanced by the cutter radius plus paper thickness. It’s not quite as accurate, as it needs measuring the cutter across edges and the paper’s thickness, and not advisable when the face is already finely finished, or is a jig or vice-jaw, but still sufficient in many cases.

Occasionally the datum is entirely within the part’s surface and the distance to the edges not critical within reason. Then you can pick up the edge, or marked-out datum centre-lines, by eye, using a finely-pointed probe in the collet or a drill chuck.

Existing, cylindrical datum holes can be located with an accurate cone or peg in the collet. This works the other way round, so to speak. The workpiece (in a vice or not) is allowed to float along and across the table, then using the quill the cone or peg is lowered gently into the hole so it just nips it against the table. Lock the quill then clamp the work, and nullify the dials. This is often used to centre a rotary-table or spin-indexer under the spindle.

 

With all these methods, observe the usual rules about table direction to obviate backlash errors.

[jaCK HobsonParticipant @jackhobson50760]

I’m a bodger,  not a precision engineer. I use my cheap edge finder a lot. I have DRO.

[old martParticipant @oldmart]

I have one of the electronic edge finders with the 10mm ball which gets used occasionally, but as the body is 20mm an R8 collet is needed to hold it and smaller spindle machines would have trouble. 95% of the time, its simply knowing the rad of the cutter and running it until the smallest touch on the work. Zero the axis used and add the rad for a centre measurement or the diameter for cutting the other side. Backlash must be allowed for if moving in the opposite direction. I have never used one of the rotating edgefinders.

[PeteParticipant @pete41194]

I guess to state the obvious, needing an edge finder would be a factor of what your doing Jon. Laying out rough bolt clearance holes on say full size farm equipment would be a whole lot different than something like clock making or producing interchangeable parts and locations. You didn’t say, but just in case you don’t already know of it, finding out and grasping the concepts behind what’s called the Cartesian Coordinate System was a huge step forward in my knowledge and understanding. https://en.wikipedia.org/wiki/Cartesian_coordinate_system And accurate edge finding would be one of the requirements to use it properly.

Using known and fixed part datum points to work from or towards is multiple times more accurate than a simple hand layout and center punching. But a whole lot of very well done Model Engineering was done in that way as well. Today I just think there’s better, faster, and much more accurate techniques available. Again and without a dro, then normal compensation for any feed screw backlash would of course always have to be done.

What isn’t usually mentioned, and in my opinion is extremely important. Is how and why those edge finders work with enough sensitivity to be useful. Even the known brand name industrial quality one’s usually aren’t all that expensive. With those, there made from very good heat treatable steel, the working parts are properly ground to size after the hardening, and for the better one’s, the two working faces are high precision lapped to be very flat and with the best possible surface finishes. It’s for those reasons the slightly more expensive edge finders are as sensitive and repeatable as they are. Buying whatever you can easily find at the lowest possible price isn’t going to get you that. Even using the incorrect or a heavy oil between the working faces can drastically affect there sensitivity and how much drag or force is then required to get them to kick at the same known point once the part edge is found each time. They also require gentle cleaning and a drop of light lubrication from time to time as well.

Like most methods, there most definitely not the only technique. I sometimes still use the very old school method of using a cigarette rolling paper between the part edge and the cutting edges of a drill or end mill, and either under rotation or stopped. The papers I’m using measure just about exactly .001″ / .025 mm. For any tool I do have under rotation, the end of the paper is gently held with a small pair of pliers just for my own safety. Move the table and part slowly towards the spinning tool with the paper between them. Once the drill or end mill flute begins to rip that fairly delicate paper, I generally assume I’m within about .0005″ / .012 mm, plus half the tool diameter. It also takes a slow approach and delicate touch until you’ve done it a few times. And that method can do something no other edge finding method I know of can accomplish. It can indicate or help compensate for any tool run out that’s present. The accuracy your own parts require should in my opinion always dictate whatever method your using.

A DTI rotated in the spindle can also pick up and help find with a very high degree of accuracy part edges and already established hole C/L’s. A Goggle search for mill spindle indicator should pull multiple images up, and making your own to fit your mills spindle diameter wouldn’t be hard. With one, some simple math and that backlash compensation, it’s no different than any other method. And it was generally the favored method for the best high precision work done on manual jig borers. There’s also some far more expensive and more niche tooling available as well. Co-ax indicators or a few different industrial level and high cost versions of my Haimer 3D. But a good DTI will do just about everything they can, and at least as accurately. Although probably a bit slower. But with smaller mills, the DTI wins over them for just how much less Z height it takes to use. For the best cost effectiveness and smallest amount of that Z height used, it would still be hard to beat a decent edge finder.

[Ian Newman 1Participant @iannewman1]

Hi,

You need to locate and reference off of edges somehow, having a DRO is nothing to do with it.

I use cigarette paper (the pages of the old yellow pages directories were useful too.  They were 1.5 thou).

A ‘sticky pin’ is my weapon of choice for locating on crossed centrelines.

Ian

[Gary WoodingParticipant @garywooding25363]

To do any work, manual or machining, you need to identify one or more reference points on the workpiece. Edges are useful reference points, and edge finders are useful for locating them. I use one a great deal.

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