Method of making expandable and collapsible mandrel

In a method of making an expandible and collapsible mandrel comprising the steps of providing a central support and supporting a plurality of longitudinal segments for movement toward and away from said support, the improvement comprising the steps of forming circumferentially disposed intermeshing fingers on said segments so that said fingers cooperate to provide a substantially cylindrical supporting outside surface at each of an infinite number of effective diameters and so that said supporting surface at each effective diameter is free of longitudinal gaps which extend the full length of said longitudinal segments, and machining said segments and their associated fingers at a position intermediate a minimum effective diameter and a maximum effective diameter thereof to define a perfect right circular cylindrical surface at such intermediate position and a substantially right circular cylindrical surface at all other effective diameters.