Perp question

[DB not cooper]

I have to planes to check perp on, they are the right and left side of the same part. perp is called out to 2 Datums, primary datum is the back of the part and secondary datum is a line between 2 holes drilled into the back of the part. now if I level to the back of the part then rotate to the line, the perp comes out good, but if I check the perp to just the line it's way out. what's the correct way of checking to 2 datums in a FCF? using 2014 software.

[neil.challinor]

Your first approach is the correct way to do it. When doing Perpendicualrity of a plane to two datums it is the orientation of the feature to the primary datum when viewed in the direction that is constrained by the secondary. Think of it kind of like doing a 2D angle measurement between your primary datum plane and your measured plane with the secondary datum functioning as your workplane.

In summary, Level to your back face (primary datum), rotate to the line between the two holes (secondary datum), then report perpendicularity of your measured plane to the back face.

[UKCMM]

If the drawing has a tolerance for both datums then they are controlling two orientation of perpendicularity and from the OP description of the layout that is very possible and they will need to call out each separate.

[DB not cooper]

Your first approach is the correct way to do it. When doing Perpendicualrity of a plane to two datums it is the orientation of the feature to the primary datum when viewed in the direction that is constrained by the secondary. Think of it kind of like doing a 2D angle measurement between your primary datum plane and your measured plane with the secondary datum functioning as your workplane.

In summary, Level to your back face (primary datum), rotate to the line between the two holes (secondary datum), then report perpendicularity of your measured plane to the back face.

now if the planes i'm checking perp on being left and right where left to right is the X axis and front to back being the Y axis and up and down being the Z axis. What workplane do I use? when I use YPLUS the perp comes out good less than .002". when I use ZPLUS it's bad. worst one is .005", and XPLUS is out in left field 3 plus inches.

[SingularitY]

I thought when using a datum inside a perpendicularity dimension, it calculated the answer regardless of workplane or or alignment as long as both feature are 3D. When I see perp with 2 datums, I create an alignment, make sure I'm in the correct workplane, and dimension perp to no datums, which should calculate it to the current alignment.

[DB not cooper]

now if the planes i'm checking perp on being left and right where left to right is the X axis and front to back being the Y axis and up and down being the Z axis. What workplane do I use? when I use YPLUS the perp comes out good less than .002". when I use ZPLUS it's bad. worst one is .005", and XPLUS is out in left field 3 plus inches

[SingularitY]

Can you attach a snippet of your print? X workplane would be wrong for sure. Imagine if you were looking at the part in that workplane while using your alignment. You'd be looking at the face of the plane. You wouldn't see any angle. (If I'm imagining your part correctly.) Making a guess here on the callout, I would say Y axis is correct based off of the alignment you described. You'd be able to see the angle deviation to the datum line in that workplane, but please post the callout if you can so I can tell you for sure.