The manganese liners require a solid base to fully bear against, due to the immense forces put upon them -- both from the crushing work, and from the movement that the work hardening process creates.

Without a substantial base for the part to bear against, the manganese itself would soon fail due to fatigue. There have been a very few crusher manufacturers that have tried to provide metal-to-metal fit cone parts. To provide fitted tapers that bear line on line in a machined state requires very good quality machine tools... too good to be viable in the machining of manganese steel. Not only does manganese work harden with crushing action, but machining the parts hardens them as well.

Manganese steel is a difficult material to machine; it's very hard on both the tools and the machines. As a result, maintaining equipment well enough to provide the kind of accuracy required for fitted machined surfaces hasn’t proven to be cost effective.

The additional time required to machine a part to this degree of accuracy raises the cost of the parts considerably, as well. Most crusher makers have found that shorter, more accurately obtainable machined surfaces on cone crushers is the most viable solution. Filling the remaining casting voids with backing material has proven most effective.