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The results of laboratory investigations and shop experience related to the machining of the alloy systems of columbium, molybdenum, tantalum, and tungsten are presented. Material properties and their relationships to maching characteristics are discussed, as are certain economic aspects of shop practice. Empirical data are presented to illustrate and quantify the more significant characteristics, and conclusions are drawn for appropriate shop maching conditions. In general, these metals are very difficult to machine; the most notable exceptions are the infiltrated forms of tungsten, whose extraordinary maching characteristics approach those of the light metals, and the molybdenum group, which are readily machinable by certain processes. However, grinding any of the refractory metals is slow and difficult, and very smooth finishes are exceedingly difficult to obtain.

To meet the extreme design requirements for strength and erosion resistance of an advanced solid propellant rocket motor, a unique reinforced plastic fabrication process has been developed. An analysis of the process provides a state-of-the-art reference point from which trends for future design, material, fabrication, and quality control requirements are discussed.