[elbruz]

Please accept the following approach that describes how to find the center of a hole with edge finder with a DRO equiped machines. Yes, I know, i did not invent this technique , but honestly to say i could not find a good explanation which explains the “logic” and “math” underlies it. All folks explain something , do like this and that, some videos without explicit description , bla bla bla etc.. So, i figured out this drawing to help the folks to understand the “logic” and “math”. I do not want to do something by heart, in contrary i want to understand the logic first, then i can reach the goal with many ways. So, believe that Math does not decieves us. Hope it helps and hoping for appreciation.
As it is clear from figure that “Middle points of any lines in X and Y inside/outside of a circle intersect in the middle of circle no matter where you start the X and Y lines from”

Lets give an example:
Start with any point in the circle and touch the edge finder and find the edge and lets name it as X1 START and zero the X1 START. Then move towords to X1 END and find the edge again. Calculate the distance between X1 START and X1 END. Lets say it is 30mm. Come back half the way and minus the half diameter of edge finder and zero . Lets say edge finder diameter is 10mm. So; we have to come back 15-5=10mm. It is middle of X1 line.

Then move again 10mm towards X1 END. And zero Y1 START. And move towords to Y1 END. Lets say distance is 40mm. Again come back half the way and minus the half diameter of edge finder and zero. So; we have to come back 40-5=35mm. It is middle of Y1 line.

Finally, if we move the X1 axis until it becomes zero (-+10mm), then we will find the middle point of the circle.

Example 2 : As it is clear from figure, it does not matter where if X2 and Y2 starts from. In both examples, lines intersects in the middle.

So, once we found the middle point of a circle, we can use a BOLT CIRCLE CALCULATOR and we can do the hole as we wish.

NOTE: These examples can be figured out with many easier ways. I just gave the examples detailed in order to get the logic.
NOTE: If there has been any error in my explanations or any point that i missed, please feedback.

[vegipete]

You don't need to do any calculations involving the diameter of the edge finder!

Just move X until you find one edge, and zero the DRO. Then move X the other way and find the other edge. Note the X reading and move back 1/2 this amount. That's X centered. Repeat for Y.

This also works on the outside diameter of a circle.

[aarggh]

That's the beauty of the DRO, takes all the complicated maths out of the equation (pun intended)!

cheers, Ian

[elbruz]

Yes right "vegipete". It was mentioned in order more clearity. But,when i read again and again it makes confusion. So, as you mention "You don't need to do any calculations involving the diameter of the edge finder!"..
So, do not take the edge finder diameter into consideration.

Wishes.

[newman55598]

You are using both halves of the edge finder so they are already included. If you have a 1 inch circle and a 1/4 inch edge finder the distance at dead center of the circle for inside edge to inside edge in a perfect world would be 3/4 or .750 as your not able to jog the extra .125 in both directions equalling the edge finder. Then you divide .750/2 and come off the edge of the circle using your edge finder .375 and you should be dead center.

[vegipete]

And if you are lucky, your DRO has a center function anyways, which divides the displayed value in half.