Hello, I have a question about composite data control frames, in particular how PC-DMIS calculates perpendicularity.

So I have a part with many 0.130 diameter holes going through the -A- plane. The company we are making the part for designated that they have to be perpendicular to -A- plane within 0.010.

The composite frame is structured like the picture I included.

DOUBLE CONTROL.jpg

So my issue lies in how exactly does PD-DMIS determine perpendicularity? My understanding is that when it takes hits in the holes it takes 4 hits near the bottom and 4 hits near the top then constructs a cylinder.

Then it takes the worst deviated point on the bottom and the worst deviated point on the top and connects them with a line to compare to -A- plane. Our -A- plane is measured by taking about 30 hits under the part.

We have issues where sometimes it says the holes are not perpendicular withing 0.010 of -A-. I find it really hard to believe that this is true since you can put a gauge pin in the hole and check it against -A- and it appears to have zero deviation. Also the holes pass for location but not perpendicularity.

Maybe our constructed -A- is not flat enough and is throwing out our holes? Any help would be appreciated.

DOUBLE CONTROL 2.jpg

So I have a part with many 0.130 diameter holes going through the -A- plane. The company we are making the part for designated that they have to be perpendicular to -A- plane within 0.010.

The composite frame is structured like the picture I included.

DOUBLE CONTROL.jpg

So my issue lies in how exactly does PD-DMIS determine perpendicularity? My understanding is that when it takes hits in the holes it takes 4 hits near the bottom and 4 hits near the top then constructs a cylinder.

Then it takes the worst deviated point on the bottom and the worst deviated point on the top and connects them with a line to compare to -A- plane. Our -A- plane is measured by taking about 30 hits under the part.

We have issues where sometimes it says the holes are not perpendicular withing 0.010 of -A-. I find it really hard to believe that this is true since you can put a gauge pin in the hole and check it against -A- and it appears to have zero deviation. Also the holes pass for location but not perpendicularity.

Maybe our constructed -A- is not flat enough and is throwing out our holes? Any help would be appreciated.

DOUBLE CONTROL 2.jpg

## Comment