max inscribed vs least square

[Kevin Watts]

good afternoon. i have been checkng a diameter with less than 180 deg of arc. i use max inscribed and our customer is arguing that it is incorrect and that the national standard to use is least scuare. i believe that for the fuctionality of the feature that max inscribed would be most accurate, but still the customer said that it did studies and has proved least square to be the best, not to mention the national or even world wide standard. Is there an actual standard for this, and is least square most accurate.
thanks

[Wingman]

Just my 2 cents but neither of them are accurate for less than 180. Max Inscribe would be (IMO) the least accurate as it really needs three 'opposed' points to be of any value.

Good luck with extrapolating a good radius from less than 180°. Some will tell you no problem and others will say it is a problem. I am of the latter and say use profile for anything less than 180.

[Underspec]

I would agree upon the application of the feature being measured. I have not heard about any standards for diameters. Do what the customer wants. They are always right

[bw_bob]

As far as a standard I'am not aware of one. As far as max vs least it depends on what I'm measuring. A machined part least is adequate on a plastic part I would usually use max...just depends.

[#2#]

What size diameter?

I would assume you used max inscribed because it is and internal feature (hole). What is the mating part like?

Least squares may give you the closest result to a bore mic or other similar measuring device. It will not give you the maximum pin size that will fit in the hole. Nothing can duplicate pin gages for that.

[Cumofo]

WIngman has a point. Profile is the best way to verify a circular feature of less than 33% of arc. I would also agree with your customer on the least square regression algorithm for any arc near 180º+.
Looks like you made the feature undersized eh?




G

[inspector212]

We use max inscribed on full circles and least squares on 90 degrees and up and profile on anything less.

I have gotten wierd numbers when using max inscribed on less than full circles.