DATUM QUESTION for Faro Arm Inspection/Verisurf

[haroldm9123]

Hey guys,

Im trying to figure out a part i have in front of me, usually its easier but for this one i am kind of confused.

i have enclosed a pic of the part in question. Datum A is the underside of the part. Datum B is the hole axis and Datum C is the other hole axis.

The question really is since datum A is the (floor) of the part, the Datum Origin is the intersection of a theoretical line to the intersection of Datum B and Datum C.  Does orientation affect the Datums? For instance the projected line from Datum B to C could really be at any angle.

Sorry if this is confusing but if you have an obvious answer to this please feel free to make me fee dumb! haha...i welcome it please.

 

thank you for any help in advance!!

 

 

 

 

 

[Metallic]

I am not totally clear on the question, but why dont you create separate planes with G54...55...56 offsets to represent each datum. Are the datums used for setup? That is a key piece that's missing in your description

[haroldm9123]

Sorry for the confusion.

This is not for machining. I am inspecting the part with a Faro Arm. I know the 3-2-1 rule and its really just to lock the part in place for proper recording of the measurements. Ill update the title, thank you!

[88Matt]

You might try locking Y on hole B and x on hole C.

[Aaron Eberhard]

I've been out of the CMM game for a while (and I was never as clever as a full time operator), but I agree with your initial assessment that there's no way to "lock" the X & Y rotations around a hole axis, only to establish the Axis perpendicularity (axis Z) to Datum A (in this case)..   So I would think you'd have to establish another measurement to align the two holes to, either the short straight edge (image 2) or the long edge (image 3).  

[RLeuschen]

Any chance you can show the 'feature control frame' and what your measuring in a little more detail? The datums on your pictures do not seem to be complete. As Aaron said, to create a line between points of a hole (top/bottom), would seem to mean its either an angled hole and everything is designated to the alignment of the angle at the -a- datum plane or its trying to prove perpendicularity on each measured feature . With no other controls/conditions listed, this would prove almost impossible to measure true positioning or anything else... without another alignment feature/datum. In GD&T, a lot of times a datum will have a specific control frame defining it (this might help)...  Then again, some new designers seem to think we on the floor just know how its defined and then its off to the design room for a pow wow. It might be time to bang on someone's door for a little clearer 'feature control frame'.

[J Barnes]

Hi Harold,

Did you get this issue sorted out.?

When aligning with verisurf you can define locks on your alignment targets.

 

[Matthew Hajicek - Singularity]

If the inside floor is datum A you'll need three datum targets to define a plane.  That surface will not be perfectly flat, which means you'll get different results depending on where you pick up the plane.