2-2-2 iterative alignment

OK, I would ignore the target points and establish datum from machined features. You could reference the targets in report if required.

Talk to the whoever programmed the NC cuts and your machinists.

If they are supporting the part or clamping on those datum points, then you should try to match what they're doing.

I wouldn't just ignore the targets until you do that.

That being said, if you're just checking completely machined parts, the datum targets may not be important any more.


If you start with a casting, it typically works like this: (can have a lot more CMM programs, simplified version)

CMM Program 1: Casting using datum targets > CMM Program 2: 'in process' tape with datum targets transitioning to print dimension datums > CMM Program 3: final inspection to print datums

So I also emailed my instructor at hexagon a few hours ago, and he said I can't use those points indicated on the print for an iterative alignment. Unfortunately, I'll have to keep ignoring them for now.
thanks for your guys input.

It has been my experience that some of the PC-DMIS instructors know how to use PC-DMIS and they don't all have experience with inspection or manufacturing. Since the 6 target points are enough to locate the part for machining, they will be enough to inspect the part as well.

If I was programming this (I thought it was one of my valve parts for a minute) I would first pick up the part with the machined surfaces (using one of the mate faces, the center of the valve bore, and one of the shaft bores). Then from there I would program the 6 target points as auto vector points. Select A1,A2,B1,B2 as your Level points. Think of it as a cylinder sitting on 4 points, it will fall into place. Then Select all 6 points for rotate, and both C1 and C2 for origin. Re-read what the Iterative alignment is asking for. It asks for a *minimum* of 3 points for level, *minimum* of 2 for rotate, and *minimum* of 1 for origin. The diameter of Datum A is given as 2.150. This is a basic dimension so it will never change. With the diameter and 2 points, you can generate a circle for A. It isn't shown, but I am under the impression that diameter B is also the same 2.150 basic diameter.

The intent (I think) of the drawing target points is to level the (2 A's B's) sides of the cast OD (like a cylinder) then clock the rotation with C's, for a start machining set-up.

I think you're "spot on" along with ctw00's analysis.

I think you're "spot on" in this assessment (along with Tater) below. I would say, however, that it "is" shown that A and B are the same singular cylindrical diameter as their targets are same diameter locations in section D-D (just different heights), and print has no lines indication surface changes.