Checking parallel or Perpendicular face 3

[Nahid Mubin]

How to check whether two faces are parallel or perpendicular in siemens NX? Note that by measure tool angle between two faces can be measured. But does that angle 0 degree or 90 degree ensures parallelism or perpendicularity in NX? For example, in solidworks if two faces are parallel or perpendicular measure tool will say parallel or perpendicular. But if the measure tool says 0 degree or 90 degree that doesn't mean the faces are parallel or perpendicular. It means there is slight deviations such as 0.00000000004 deg or 90.000000001.

 

[3DDave]

Welcome to floating point mathematics where the conversions from the binary representation to decimal and back loses precision. Want more fun? There is a chance that a planar surface doesn't have co-planar verticies.

This is why there are tolerances, typically called epsilon, to represent what deviation is considered significant.

See: What every computer scientist should know about floating-point arithmetic

https://www.itu.dk/~sestoft/bachelor/IEEE754_article.pdf

one of great number of places that has this document.

From the document: "the decimal number 0.1 cannot be represented be represented exactly but is approximately 1.10011001100110011001101 x 2^-4."

 

[Toost]

Way back in time i used a cadsystem which used "single precision". ( late 80:ies) It was fully normal back then that when one had drawn a few lines , building the lines from each other , that when placing dimensions on the drawing, we had to strip away the decimals since a mesurement that intentionally should have been say 185 turned out as 185.01.

That said, the other cad systems seems to have an IF statement that "if angle is < than +- 0.xxxxxxsomething, then print : "Parallel / Perpendicular"

Regards,
Tomas

The more you know about a subject, the more you know how little you know about that subject.

 

[yy912]

The non-perfect parallel/tiny tilt angle will be a problem mainly when I need to apply constraint.
Here is the way I check if there is a tiny tilt angle:
If it's a not perfect 0deg, the angle measurement result will show the tiny angle like 3.364e-8. In this case I know it's not perfect parallel and needs to be fixed. If it shows "0.0deg" it should be a perfect 0 deg, at least it won't result in trouble when adding constraint.
But it only works for tiny angle around 0deg.
For 180deg, it can be turned into 0deg by switching between measurement options of "Inner Angle" "Outer Angle" or "Supplementary Angle".
For 90deg, a workaround can be finding a trustworthy plane as datum, and turning 90deg measurement into 0deg.

NX 1919 Windows 11