Abstract: A spruing assembly for receiving investment material in the production of an investment mold for castings by the "lost wax" process which includes a hollow chamber to receive the investment material. Included within the chamber is one or more sprue for supporting the wax pattern(s) to be cast and one or more corresponding predetermined shaped reservoir(s) being slidably moveable up or down the sprue to create the heat center of the investment mold. Where a long span casting is to be produced all the reservoirs are connected to form a continuous reservoir or Feeder Bar which conforms to the curve of a long span dental arch. A base member is provided within the chamber for supporting the sprue.