Problems with object orientation and angled array I need my glass panels to stick to the metal frame of my building. The axes are set to global and I've tried CTRL+A and CTRL + ALT + SPACE but nothing works.



I need my Y arrow to be perpendicular with the object and the X arrow parallel so that the glass panels array in a straight line without having to change other values in the relative offset setting
Select two vertices, 
Change Transformation Orientations to Normal,    
Press the add button in the Transform Orientations panel then
Select new normal, ie Edge, in the drop down list.





In Object mode, shift+S > Cursor to selected,
Shift+A  > Empty > Plane Axes,
Set the constraint as shown in the figure and
Move Empty object using added normal(Edge).