Find the focal point for any dish

[Gugi47]

This process requires a straightedge like a yard stick or meter stick, a marking pen, cardboard with a straight (square face), and a pair of scissors. This will be an exercise of Physics at it basic elements. It doesn't matter what the support arm angle is, it doesn't matter if the dish is oval, elliptical, round, or even a rectangular dish.
The only thing you need is the original LNB....beg, borrow, or appropriate one for this short term project.