GD&T for Holes are in Angular face

[ashivu123]

If the holes or any are located in angular face do we need to make angular face as datum? In order to locate the hole on the face. I have attached drawing in which 1st set rivet holes are located on planar face and other 2 sets are located in angular face. For 1st set rivet holes I used composite tol frame per guidelines created here. Can I use same Composite tol frame for other rivet holes which are located in angular face? Since the bottom frame as one datum pattern must be controlled w.r.t that datum.

 

[3DDave]

The problem this poses is that the axes of the holes are not dimensioned to their intersections with datum A and they are not given a basic angle to datum A. As-is the slope of the holes eats into the allowable, but unknown angular tolerance on the control of the axis. For example, if the slope is 30 degrees, and the material is .1 inch thick, the axis displacement to A|B|C is sin(30)*.1 = .05 inches, for a positional diameter of 0.100, which is a bit larger than the tolerance.

What would be better is to establish a small taget area around each large hole as datum E and locate the countersunk holes to [E|D|B] INDIVIDUALLY. The primary thru holes should have the axes dimensioned to their intersections with A and given a basic angle to A. This duplicates how the drill will be positioned to create the holes.

This is necessary because the tolearance is on the entire axis of the hole, not the intersection of the hole axis with the 'obvious' side. This intersection will float depending on the angle of the bend.

 

[emorrison]

Design intent in relation to datum assignment seems a little off with this example but that aside, I don't see the purpose of datum D in light of C. Pick one or the other as tertiary.

Call out the angle, make it basic. Assign D to this callout/surface. Profile of surface on "D" tied back to A|B|C. Basic dimensions from A & C to each hole on D (intersection with surface D). 2 feature control frames; true position A|B|C, true position D (controls perpendicularity).

 

[ashivu123]

Thanks Dave ane Emorriso,

I got it since the hole are located in angular face need make angle as basic for true position. However does need to make entire surface as basic angle or only hole need be located with basic angle?
Let me know which datum would be there in lower compartment for c'sunk holes which are there in angular face?

 

[ashivu123]

Usually we specify "TRUE" to hole callout in order to avoid specifying angle for holes which are in angular faces.

 

[3DDave]

For my suggestion, the basic angle is between A and the axes of the holes. The surface is controlled separately.