Distance Measurements Not in Agreement

[[Pa...]]

I am attempting to locate a part glues onto another part using Caliper Distance, but am running into a few issues.

I am measuring the distance between two planes in the X direction with the Caliper Distance Characteristic. The actuals in the Features Tab do not at all match what is being shown in the measurement in the Characteristics Tab. Looking in the feature tab these features should be ~0.004 mm apart (nominally they should be flush, 0mm apart). Looking in the Characteristics Tab, if I take Caliper distance from the from measuring points the result is an order of magnitude larger. The form of both planes (or at least the points measured) is less than .001 mm, so I'm not sure where the difference is coming from.

[[To...]]

When looking at the X, Y or Z values of a feature, you need to understand exactly where the point is. On a plane, it is typically in the lower left hand corner, but more specifically, at the feature's trihedron. You mentioned the form was good but did you observe the A1 or A2 projection angles? This also impacts where that X, Y or Z point is located.

On some distance characteristic, the order of the features determines if a plane is a datum feature, which controls the orientation of the distance and the other plane is measured to the mid=point of the plane.

There is also the affect of filters and outlier elimination and whether they're applied to the feature or to the characteristic.

Hope this gives you some direction.

[[Ri...]]

The Caliper Distance tool uses an alignment to create the distance. If the planes are parallel/perpendicular to the alignment, then your results will be skewed.

I would try using the Cartesian Distance tool first. In this case, the order of precedence matters - so (if it's two planes) try placing the larger of the two planes as Feature #2.

[[Pa...]]

Please sign in to view this quote.

The projection angles are matching. As far as knowing where the points are, do you know where I can view the X/Y/Z of the individual points on a feature? I have not yet been able to find just the raw points.

I am using Cartesian Distance, and determining from measuring points. Changing order does not change the value

I am taking single points so not filtering

[[To...]]

If you right click on a feature, you can select "Export Points" and that will create a text file of your points relative to the alignment.

Also, as a follow up to Richard's post, I created a quick depiction of a cartesian distance and reversing the features. I included perpendicular constructions because they behave the same way as cartesian distances but since you're creating a 3d line with a perp construction, you get a visual showing the distance evaluation.

Cart Dist_Perp Const_Comparison.pdf

[[To...]]

Please sign in to view this quote.

The "actuals" of the projection angles are matching?

[[Pa...]]

Thank you for the help everyone! After doing some more directed digging, I thought I'd share in case anyone else runs into a similar issue. it seems I misunderstood exactly how the points were selected when using the "derived from measured points" option. In my head I had it that selecting maximum in say, the X direction would just pick the points on each feature with the greatest separation form the opposing feature in just that direction, but after comparing which points were being selected, it looks it is taking into account the 3D position of the points when selecting a maximum or minimum point, which does not output a representative result in my current measurement setup.

[[Jo...]]

Please sign in to view this quote.

Richard,

So, when using Special Geometries, Symmetry plane, how does it determine a vector to establish a distance ?

You can select evaluation method to get a minimum or maximum distance.