0.005 difference at flatness measurement.

[quadrille]

Hello everyone,

We got a part that has 104 points pre-determined acc. to technical drawing. We measure that 104 pts then take a plane. Let's call it Plane 1.

Flatness of plane 1 (minimum seperation method) is 0.754

After that, We select plane 1 as reference datum and re-measure 104 pts but distance from max and minimum points are this time 0.759

Do we have clear explanation about this difference or is it just machine permisable error ?

Thank you.

[Paul Sarrach]

Is that in inches? Metric? What is the tolerance? And what is the part? With it not being very flat you could have deflection issue here. Run it a couple times and compare your results..

[Quality ish]

What do your vectors look like in the program? A wise man recently told me: "Clean up your vectors!"

[QS920]

Thanks! Well said.

[UKCMM]

The vectors of the hits used to make Plane 1 are going to be based on whatever alignment the part was setup with. By re-aligning on that plane the vectors will now be based off that new plane and may well be different causing small changes in the hit positions and given the large error no real surprise to see a change in calculated value.

You will also have some error from the probing/machine/calibration/environment/ and may other factors that affect repeatability of measurements.

Have to ask why measure the 104 points two times as if the first run is only to establish the alignment then it is somewhat over kill.

[NinjaBadger]

Hello everyone,

We got a part that has 104 points pre-determined acc. to technical drawing. We measure that 104 pts then take a plane. Let's call it Plane 1.

Flatness of plane 1 (minimum seperation method) is 0.754

After that, We select plane 1 as reference datum and re-measure 104 pts but distance from max and minimum points are this time 0.759

Do we have clear explanation about this difference or is it just machine permisable error ?

Thank you.

Assuming it's metric then this will probably be down to machine repeatability.