4.1 / Best Fit Circle question

[bob mappes]

I have a part that I am trying to apply Best Fit to a diameter, 30mm hole +.013 -0

I am taking 12 surface points around an ID and then creat a best fit circle using those hits, and max inscribed.

Now as I understand it, this is simulating a "hard" gage or plug gage, like using Deltronic pins.

now the question.....wouldn't the "form" of this "created" circle be 0 (zero)?

thanks
bob

[Cumofo]

I think your looking for max inscribed, but I'm sure the actual form is always reported.
I would be careful about using non-vectored hits in a circle. An autofeature is still the best way to go, apart from full scanning elements.
G

[Boomer]

I agree with Cumofo, scanning the diameter with that tight a tolerance is your best bet. I would definely try a correlation study between the pins and your readings.

[cmmguy]

max inscribed only uses the three highest points - scanning would give the most density to find those points. Only 12 might give you repeatability problems. Vectoring should not be a problem, but I dont understand why you use surface points instead of basic hits, auto-circle would be much easier.

Are you best fitting and then max-inscribing?

[bob mappes]

vectors are not a problem..created one hit with proper vector the did paste with pattern

best fit was done WITH max inscribe

I'm now taking 36 hits and getting better results

now here is a funny thing showing up.......
The program is created in metric due to the nature of the drawing being metric,
The results are in metric for same reason
I also have this one diameter in inches (as well as mm) due to the fact the machinists are working in inches
I added form to the diameter results (inches)
the form results on the "edit" screen are in inches but on the "report" screen show in mm. WTF?