Problem with joints and triangle shape meshes

I am trying to create a pinball paddle and have a triangle collision shape for the mesh. I am using revolute joints but have trouble to find the position for the joint axis. Is there any smart way to find the right position? As it is right now the paddle flies all over the place

Your modelling the mesh in a modeller right, and the paddle is a cube or convex shape?

Then it seems easy, make a mock up of the paddle in your modeller with the table, move the paddle to where it is supposed to be, and get the global position of the vertex, of where the joint would be on the table. Add half of paddle height to the Y axis and you have your joint position!