Iterative alignment and using XactMeasure

I'm looking for a way to get my nominals to come from the datums, not from my trihedron. Iterative alignment will align to trihedron not the datums. I guess my problem is making Datum "A" an origin more than the Iterative alignment. The Iterative alignment part of the problem is just what I thought would fix the problem, and apparently it will not. All of the information on Iterative alignments is great, but is not the answer I'm looking for. I guess all I really want to know is how do you orgin on an irregular CAD surface?

Iterative alignments are great for measuring parts in aircraft/car body coordinates, but that seems to be about it. When you need your report to measure from the datums and not the trihedron, its not effective alone.

Ignore the trihedron. Iterative alignment is a CAD alignment, or PART alignment.

A 3-2-1 alignment uses features to align, and YOU tell Pcdmis what those features need to be, nominal-wise.
An Iterative alignment uses features to align, but the CAD data tells Pcdmis what those features need to be, nominal-wise.

The ONLY way to "level" to a non-planar, non-flat surface is ITERATIVE alignment. EVERY PART has datums, even car position parts. There are "A" datums, "B" datums, "C" datums, as many datums as you want, just like for every other part out there.

DATUM does NOT EQUAL ZERO. It never has, it never will. A datum CAN BE zero, but it does not have to be zero. Datums are the "START POINTS" for inspection.

The top of a flat, square 123 block that is the "A" datum can be Z0, Z1.0, Z523.984. It makes NO DIFFERENCE. DATUM <> 0, it never has. The trihedron is nothing more than a visual aid for you to see which way each axis is pointing in the current alignment, NOTHING more. The trihedron <> 0 anymore than DATUM.

'top, curvy, non-flat' surface = "A Datum". Pick 3, 4, 5,000 points on that surface, from the CAD DATA (and the "B" and "C" datums as well). BEFORE you measure them, OPEN the alignment utility, go to iterative alignment, select all those points on the "A DATUM" surface for the "LEVEL" features, pick the "B" feature for the rotate, pick the "C" features for the origin.

Pcdmis will then "level" and "origin" to those "A" features. It will 'rotate' and 'origin' to the "B" features. It will origin to the "C" feature. And guess what? You are NOW origined to ALL your datums, no matter what their numerical value is, be it Z127.398 or Z-1928.392. Pcdmis will have them as close as possible to the nominal values as can be done.

I guess if you don't get it after all this, you either need to find some other calling or go to Pcdmis classes.

First off, HOW RUDE!!!!!!

I do not necessarily want my Datums to be Zero, (don't believe I ever said that) but I do need my dimensions to come from the Datums, not the CAD trihedron. What part of this am I not explaining well enough for you to understand. If we were talking real world inspection, not with PC-DMIS, if I set Datum "A" down on a datum feature simulator it would set on the three highest points. What I did is found the three highest points on datum "A" and created a plane out of those three points?

Call it rude, call it whatever you want.

You've been given ALL the (correct) answers, if you can't make heads or tails of it, then "chatting" on the webs won't solve it, you need classroom training.

If you are aligned to the "A" datum (321 or iterative), any dimension created after the alignment can ONLY come from tha datum, as that is what you have set as "master" (not ZERO, but "zero deviation from nominal").

Aligned to datums, ANY and ALL dimensions COME FROM the datums.

So if you have a 1-2-3 block with one hole in it 1 inch from each side and this CAD trihedron is 300 inches off in "X" and 200 inches in "Y" and I use an Iterative alignment, when I dimension my true position of said hole the nominals will be 1.00 inch each direction? Or will it be 301 inches and 201 inches.

So if you have a 1-2-3 block with one hole in it 1 inch from each side and this CAD trihedron is 300 inches off in "X" and 200 inches in "Y" and I use an Iterative alignment, when I dimension my true position of said hole the nominals will be 1.00 inch each direction? Or will it be 301 inches and 201 inches.

it depends what is selected in exactmeasure. if you make your feature control frame position to A|B|C| then go to the advanced tab, look at the alignment drop box near the bottom of the page. if current alignment is selected then the true position will be given in car line for example. However if datum reference frame is selected the distances should be from the datums you have selected in the feature control frame.

Both. Your dimensions will report out as X-301, Y-201, but the position will have been calculated by creating ABC at 0,0 and translating it 300,200.

In the case of your irregular surface that is impossible to origin on, if you aren't given XYZ coordinates for say, datum B and C, then you have no way to translate the CAD. So, leave it in body position! It is ok for your nominal to not be 1,1. The calculation was done as 1,1 translated 300,200 to comply with your CAD position.

It is NOT ok of for me to leave it in body position! My customer requirements are to have the dimensions report out from the Datums, not the CAD origin. My report would need to say 1 inch from "X" and 1 inch from "Y". I have no way of measuring Datum "A" to my CAD origin due to it being an irregular surface.