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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!
Parents
  • Good Day,

    As others have already said:
    With the T-Value or, in other words, with a surface profile, you get "repeatable" measurements.
    as long as your alignment is stable.

    maybe that's enough to decide if the area is in spec


    Unfortunately not in my field and position. The data are put on a database and the checklist that contain the ⌀ measurement are already premade. Only a ⌀ measurement is accepted in this case and a PR of the points taken would be put in a created circle that would have ⌀= 2*PR of the point (or points actually).

    @ ​ thanks for the confirmation, I would be very interested to hear the results of your tests when you find the time to investigate!
Reply
  • Good Day,

    As others have already said:
    With the T-Value or, in other words, with a surface profile, you get "repeatable" measurements.
    as long as your alignment is stable.

    maybe that's enough to decide if the area is in spec


    Unfortunately not in my field and position. The data are put on a database and the checklist that contain the ⌀ measurement are already premade. Only a ⌀ measurement is accepted in this case and a PR of the points taken would be put in a created circle that would have ⌀= 2*PR of the point (or points actually).

    @ ​ thanks for the confirmation, I would be very interested to hear the results of your tests when you find the time to investigate!
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