Using domino on obtuse angles

[WoodenGoblet]

I want to join to pieces of 1 1/4" x 3 1/4" lumber that are cut at 50 degrees using my domino joiner. Do I set the angle of the joiner at 40 degrees or 50 degrees to join the two pieces?
thanx

 

[Gregor]

Depends on the orientation of the domino.
Keep in mind that the axis of it should always be perpendicular to the surface it's inserted into.

A picture might help give you more information.