Sigma Error

[[Me...]]

Dear all
Good morning everyone
I did that calibration after checking the part and in palne sigma error is 0.016 because of this perpendicular not ok
I don't know this error meaning and How to Remove it ????

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[[Ja...]]

Are you working in inches or millimeters? If mm, 40 microns is a pretty tight tolerance! Also, it's unlikely your primary datum in this case is the axis of the cylinder itself. Try reporting that cylinder back to the plane, instead. Your "sigma" is basically your standard deviation if you were to plot all of the points taken for that feature into a bell curve. I'm not that great with statistics, but it'd be worth reading up on if you're curious.

[[Ch...]]

I noticed the form value of your plane is .0505. That is quite high considering your tolerance is .040. The high sigma value could be from the probe shanking out or anything that would cause bad hits.

[[Ja...]]

Chad, good eye! I thought the form error was 0.005. That being said, couldn't he benefit from taking less points to evaluate that plane? 10 seems unnecessary (unless it's a large part). I agree that he may have shanked at some point. Maybe the part's surface, stylus or both are also slightly dirty?

[[mo...]]

Good morning,
I am so happy to find something about sigma error in this forum.
I am wondering if you know how the software calculates this form deviation and sigma error. I didn't find anything about this topic even in the manual book.

Thanks

[[Da...]]

A rule of thumb is to multiply the sigma value with three and then compare it to the form error. In this case this would give you the value 0.0501 compared to the form error of 0.0506. A value of 3 sigma represents a 99.73 % statistical probability that the points that make up the form error of 0.0501 are valid. The rest might be considered outliers. In this case, both values are close together, which yields a high probability that the form error is correct and not based on single bad hits, so it doesn’t look like the probe was shanking out.

You need to get the flatness better, then your perpendicularly should automatically get better, too.

[[To...]]

You could try evaluating your plane using a plot.
I often find this usefull.

What is the lenght of the cylinder compared to the plane?