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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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  • Normally when i use this method i use the fixed radius and then change back to the original alignment and report out T values of each point. It doesnt give a radial value but it gives nominal surface deviation from the intended surface.

    I am not sure I follow. So you use the fix rad method to find a center or not? Not really sure how this can help in the issue I have with the accuracy of this method Disappointed
    If there is a "repeatable and accurate" way to measure small arcs other than going the least square methos, please someone list the steps because I am clearly missing something with the fix rad method.
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  • Normally when i use this method i use the fixed radius and then change back to the original alignment and report out T values of each point. It doesnt give a radial value but it gives nominal surface deviation from the intended surface.

    I am not sure I follow. So you use the fix rad method to find a center or not? Not really sure how this can help in the issue I have with the accuracy of this method Disappointed
    If there is a "repeatable and accurate" way to measure small arcs other than going the least square methos, please someone list the steps because I am clearly missing something with the fix rad method.
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