We propose a simple model of energy transfer in the course of ball milling in a vibrating frame device : the energy transferred per impact goes as the mass of the ball and the square of the amplitude and frequency of vibration of the frame. A reduction efficiency factor must be introduced, which depends on the ball rigidity with respect to that of the material being processed. The frequency of impact between the ball and the material goes as the amplitude and frequency of vibration of the frame and as the inverse of the terrestrial gravitation constant. For assessing the role of the above parameters in s tabilizing metastable phases by ball milling, a new device has been built which allows to keep good vacuum during long time milling treatments. Preliminary results on NiloZr7 point to the crucial role of the e fficiency factor in reaching full amorphization. Under good vacuum, continuous foils of amorphous material can be obtained.