Measured features VS CAD model

[silvio]

Hi everybody,

I am starting to use our new acquired CMM arm. My question is about the use of the imported CAD model in PC-DMIS measurement routine.

Until now I:
1) imported the file
2) aligned it with the actual part
3) created measured features and created dimensions for the report.

In my understanding I was using the CAD simply as a visual support for the operations.


Next I would like to do is to take the CAD as nominal geometry, and compare the measured points with the actual CAD faces.
For instance, I would like to pick points on my part and have the distance of the picked point from the nominal surface.
What I am missing is how to create a feature from the CAD.

What are the options?

Thank you very much in advance

silvio

[Roberto]

Hi Silvio welcome to the forum!
You need to do the opposite on step 3. Get the correct nominals and vectors from the CAD before you physically beep the part for evaluation.
Otherwise It's like putting the cart before the horse

[michaelwildschutz]

Or you can use cad equals part after the alignment that correlates to the cad model origins

[A-machine-insp]

On/off topic question regarding CAD=Part... To use it correctly I am assuming that the part needs to be physically aligned so the origin is in the same place as it is on the CAD model? Asking because I've never used it before.

[michaelwildschutz]

yes that is correct origins need to be the same

[KIRBSTER269]

Think of it this way. When using a CAD, you are creating the mating part for that part. You go in a hole, you create a cylinder, you've created a perfect size gage pin, You create a perfect plane, you created your perfect surface plate, once all this is done, you "could" dispose the CAD model, all you have left is the perfect mating part, Then you bring in your actual part and do all the actual touching on it and see with all tolerances given, if the 2 will fit together. That's why you will see Datum Shifts and Rotation. PC-DMIS will say, well at worse case, based off the condition of your part, parts good or parts bad.

So to answer the measured vs CAD part. You have to manually fix the vectors and measured features to be square and perfect when need be, or when possible (unless you have curved surfaces)

[vpt.se]

Enable "Find noms" and "Points only" after you have aligned the part according to the CAD model. This will generate (measured) vectorpoints with closest CAD nominal when you probe the part.

[silvio]

Hi,

Thank you very much everyone for the help, I will try the suggestions.

In the mean time I did this (it seems what roberto an kirbster269 suggested):

1. Create a plane in command mode (that is a virtual nominal plane clicking on the cad)
2. Getting points on the actual part for the same face
3. Creating distance dimension (to feature, perpendicular)

It seems what I wanted, but the distance values are actually 1 order of magnitude smaller than the measured actual flatness of the face. I would have expected to get the max distance >=1/2 flatness deviation
I keep you updated

[silvio]

I was doing it wrong. Now it is sorted out.
As you suggested:
Autofeature vectorpoints, then location dimension I get the normal distance of the real point from the virtual face.