Min Max Flatness Plot

[[Ra...]]

Hi -

I was questioned about these plots about why the min/max in the corner chart doesn't add up to the overall Flatness, and I wasn't sure. Should it? I never really paid attention until now. These were (6) diameter planes compiled into (1) plane. Note: I have a few of these scans and none come close regarding the expected ABS MIN+MAX= flatness.

Thanks!

[[Ke...]]

I would presume that the corner box values are simply "where are the min/max points located relative to the alignment", which is seperate from the Measured value that is meing evaluated to the Minimum Feature plane.

[[Ri...]]

The Max is 0.0038, and the Min is 0.0000 = 0.0038 Flatness. It's location is just where it is respective to its alignment - flatness is irrelevant to location/orientation. 

Edited May 1

[[Je...]]

What Keith and Richard said.

The likely difference between the reported flatness and the Min./Max. in the grid you referenced in PiWeb relates to the alignment that the Min./Max. are generated from.

Flatness uses minimum feature as the standard evaluation method, which isolates the unrelated mating envelope (i.e. doesn't relate to a datum reference frame).  This is a key advantage of digital systems such as a CMM.  The feature can be isolated to itself to evaluate form characteristics such as flatness.