Big ball joint

I've designed this big ball joint for hanging our beamer to the ceiling. The ceiling has a small slope (a few degrees). Futhermore, the beamer needs to be tilted a little forward for a good projection on a screen. The balljoint gives anough degrees of freedom for this task.

The diameter of the mountingplates is 10cm. The ball itself has a diameter of 3.5cm. Height between (and including) both mountingplates is 7 cm. Relative tilt from the plates to each other is about 10 degrees.