In recent years increasing interest has been shown in the use of concrete as an alternative to mild steel or cast iron for the structural components of machine tools. An investigation of the problems of using concrete for this purpose has been made in England. Several machine tool manufacturers supplied the necessary parts to assemble complete machines on concrete structures and thus made possible direct comparison with corresponding machines having cast-iron structures. A bed-type milling machine and a small capstan lathe were chosen for manufacture. Small size limestone aggregate was used to facilitate drilling of holes if needed. Conventional steel reinforcement was used.
Replacement of the bed for the milling machine posed manufacturing and assembly problems; it soon became apparent that manufacture of this bed in concrete would not be viable on economic grounds alone. On the other hand, the bed of the small capstan lathe represented the kind of structure that could probably be made in concrete more cheaply than in metal.
Indirect cost reductions such as the reduced amount of surface dressing and filling on the concrete base by comparison with such costs on the metal base may well increase overall cost savings significantly; additionally, the cost of producing components prior to final machining should be 30 to 50 percent below that of the conventional iron components. Tests still to be done or in progress concern the effects of increasing the thermal inertia of the structure and the long-term stability of the machines. Of particular concern are the effects of swarf abrasion and of lubricant and coolant on the material.