# Feeling Edgy? -- Aka: Edge Finder Anomalies



## Uglydog (Nov 3, 2015)

I've used both Edge Finders and Wigglers.
What is are they? Examples found at: http://www.starrett.com/metrology/m...isplayMode=grid&itemsPerPage=24&sortBy=wp/asc

I believe that the Edge Finders are more consistently accurate than Wigglers because the Wigglers are subject to how tight I set the nut. But, this opinion is only anecdotal. I wonder if the spring tension on the Edge Finders effects response.  Both might also be subject to my visual acuity and reflexes.

Does anyone have an informed opinion on precision edge finding?
Are there good and affordable alternatives to using a Center Scope (pdf attached)?
Does anyone here use a Center Scope regularly?

Additionally, the above methods only address X&Y. 
I'm using a piece of paper or shim stock for Z. What options are available for Z?
Personally, I'm particularly interested in old school (pre-DRO).
How do/did the Jig Bore gurus and others find a repeatedly find precision edges?

Thank you,
Daryl
MN


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## MozamPete (Nov 3, 2015)

Have you been following the thread on using a cheap USB microscope and Jim's software effectively as a center scope?  (http://www.hobby-machinist.com/thre...icroscope-aka-cheap-optical-comparator.38077/)

Myself I just use a Wiggler where necessary.  I have a horizontal mill with an additional vertical milling head so can use it in all three axis.


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## JimDawson (Nov 3, 2015)

All of the above methods work, but I find the most convenient and accurate is the edge finder.  The edge finder is the most repeatable, normally good for <0.001.

The least accurate method that I have is my spindle laser, the dot is too big for accurate measuring, but OK for setting a starting point if I have plenty of material to trim, works about as good as eyeballing a center drill point.

A centering scope works and is accurate, but requires careful setup and don't count on the crosshairs being on center.  They are only adjustable in one axis, so to locate in 2 axis you have to rotate the scope 90 degrees and use the same line for both axis.  It does work well for locating a scribed line.

A dowel pin in the spindle and a shim makes a very accurate measuring system, but does require some practice to achieve repeatability.
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## RJSakowski (Nov 3, 2015)

JimDawson said:


> ........The least accurate method that I have is my spindle laser, the dot is too big for accurate measuring, but OK for setting a starting point if I have plenty of material to trim, works about as good as eyeballing a center drill point.


I mounted a laser pen in my boring head. The 1/2" diameter of the pointer barrel fit nicely into the boring head.  This gives me an adjustable circle which is great for finding the center of a small hole or circular boss.  Most laser pointers have an adjustable focusing lens and I adjusted the pointer for the shortest focus possible which give the smallest point.  Adjusting the diameter of the ring of light to slightly under or over the diameter of the feature that you are centering on improves the accuracy.  

I put a piece of plastic tubing over the barrel and just slide it up to keep the switch button depressed.  The only drawback is the long length of pen type pointer.  A key chain style of pointer would work better.

Bob


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## RJSakowski (Nov 3, 2015)

I use an edge finder almost exclusively.  I prefer the 1/2" to the .2" edge finder.  I find that with care it is consistently repeatable to +/- .0001".  The ability of the edge finder to self center on the spindle axis removes spindle runout from the equation.  It does take some care in use however. 

To use, I select a fairly low spindle speed, about 800 - 1000 rpm. I will approach an edge fairly rapidly and note the point where it jumps.  I then back off and use my fingernail or a small piece of wood to center the edge finder and approach again as slowly as possible.  With the Tormach, I approach at a rate of about .0001"/sec.  If the edge finder is wobbling and it strikes the edge before centering, it will jump prematurely.  If you move in too quickly you can overshoot the edge before the jump.  I always make multiple runs and verify that my readings are consistent. 

The edge finder works very well in finding the true center of a piece of work.  Find one edge and note the position.  Move to the other side and find that edge and note the position.  The true center of the work is the average of the two and removes backlash from the measurement.  If backlash is significant, you can correct for it by adding half of the lash to the location.  e.g.  If I were centering in the x direction, I would find the left edge of the workpiece and zero the readout at that position.  I would then move to the opposite side, keeping the same y and z position, and find the right edge of the workpiece.  The true center is the average which is 1/2 of the right edge position.  If I had .002" backlash, I would move to the calculated center position and add .001" if I were counting up or subtract .001" if counting down. 

The edge finder also works well for finding the center of circular bosses or holes.  To find the center of a boss or hole, I would visually position the y axis and locate the left edge.  Keeping the same y and z axis, I locate the right edge and set my x axis to the center of the piece.  I then repeat the procedure on the y axis, keeping the x and z axes fixed and set my y axis to the center of the piece.  Finally, I go back and relocate the x axis center.  (The reason for doing this is that on a circular object the contacted edge will not be parallel to the y axis if you are not on the center in the y direction.)  For holes, a smaller edge finder generally works better than one which is close to the size of the hole.

Bob


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## Line_Bore (Nov 3, 2015)

An edge finder, as mentioned can be accurate to less then .001.  Check for smoothness by sliding the nose across the shank (gently). Cheap finders sometimes need a little lapping, but they work well.
The most accurate way to find an edge is to swing an indicator to zero on the workpiece, then hold a gage block to that edge and get to zero. You will be tramming the same plane 180 degrees apart
Move the part until you get zero on both sides. It take a little more time, but it will be as accurate as your equipment allows.

Sent from my LG-H345 using Tapatalk


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## Line_Bore (Nov 3, 2015)

Line_Bore said:


> An edge finder, as mentioned can be accurate to less then .001.  Check for smoothness by sliding the nose across the shank (gently). Cheap finders sometimes need a little lapping, but they work well.
> The most accurate way to find an edge is to swing an indicator to zero on the workpiece, then hold a gage block to that edge and get to zero on the face that's against the part. You will be tramming the same plane 180 degrees apart
> Move the part until you get zero on both sides. It take a little more time, but it will be as accurate as your equipment allows.
> 
> Sent from my LG-H345 using Tapatalk





Sent from my LG-H345 using Tapatalk


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## wawoodman (Nov 3, 2015)

Uglydog said:


> Personally, I'm particularly interested in old school (pre-DRO).
> How do/did the Jig Bore gurus and others find a repeatedly find precision edges?
> 
> Thank you,
> ...




Cigarette papers and a little bit of spit to stick them down.


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## stupoty (Nov 3, 2015)

I've got a starret edge finder, I was fidling about in the workshop one day doing a bit of tidying and organising and became curious as to how well it reppeats.

Turns out very repeatable, was less than a thousandth without too much faffing about.

Stuart


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