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Question about the small arc method

constadin
Hello all!

Please let me know if I am doing something wrong following the small arc method.

Btw, I am using vector points and auto circles with NO CAD always in DCC mode. Let's also assume that I am measuring in Z plane.

1) I am measuring the small arc with a fixed radius auto circle.
2) I am setting my origin XY to this circle.
3) Just to be sure I am repeating with a new auto circle fixed radius and realign to it.
4) I am taking 3 vector points in polar coordinates to be precise.
5) I am reporting the PR of the points.

This morning I had a 80deg on an arc R2.8mm to measure. I used this method and I was getting repeatable results at 2.80. The issue is that the radius has been measured to be 2.75mm (verified with 2 other methods also).

I also tried to change the fixed rad value based on the R measurement I had performed before with least squares (around 2.75 non repeatable value) and I was getting results close to that value (the least square value).

With this method, does the fixed Radius value provided alter the centre that is being found? Doesn't this beat the purpose of using this method?

Thanks in advance!
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  • If you are using the fixed radius method and then report out the polar radius of the hits after you will get results mirroring your fixed radius value since the origin of the circle is moved from the surface by the radius value input.

    Exactly, so what is the point in using this method in the first place? Am I doing something wrong? I am missing the point somewhere and unfortunately no reply has yet to shed some light on that :S

    Btw: @ ​ This is not the method that is suggested from hexagon though :S Approaching the real center with a fixed rad and then taking a least squares circle is not much different that establishing a good alignment on a good cnc machined part (as in this case) and measuring it directly.

    @ ​ I took enough points to create the fix rad (9 points on such a small arc) and 3 PR points well placed on the arc after that. All of them had 0.05 mm difference from the real value and taking an average isn't really improving the outcome.

    @ ​ not really sure what you mean. Is my method wrong? Should I do something different?

  • in reply to constadin
    Try my method and see what you get. First, create an Alignment offset to the theoretical center of the arc and construct an Origin Point in that alignment. Then follow the steps in my initial comment.
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