Constitution Bench - When can be constituted?

Article 145(3) of the Constitution of India 

                                        Only substantial questions involving interpretation of the Constitution shall  be heard by a Constitution Bench, and other ancillary questions can be referred back to a smaller Bench to decide.

               Please see : 

                                         Rao Shiva Bahadur Singh v State of Vidhya Pradesh, (1955) 2 SCR 446