Cutting force monitoring of chain saw machines at the variation of the rake angle

The present research aims at consolidating the theoretical aspects related to the use of chain-saw machines in the quarrying of marble. Cutting conditions conventionally adopted during quarrying operations have been reproduced in an experimental set-up and forces exerted during the material removal have been monitored by means of a piezoelectric dynamometer. With the objective of avoiding drawbacks in the process monitoring which might arise due to accelerations of the tool in linear motion with respect to the workpiece, the orthogonal cutting process was obtained by inverting the relative motion between the tool and the stone. White Carrara marble disks were put in rotation using a lathe spindle and the effects of each tool composing the pitch of the chain saw were analyzed by signal processing. Therefore, the complex action of the chain into the stone has been decomposed into stable orthogonal cutting conditions by analyzing the forces exerted during the removal process using each tool singularly. Once established the capabilities of the standard tool geometries, three main tools characterizing the deepening of the chain into the groove, were tested by varying the rake angle γ. An especially conceived fixture was designed and realized to vary the rake angles up to negative values with the objective of increasing the compressive action under the tool tip and thus favouring the material removal by crack propagation. These hypotheses, derived from basic principles of rock mechanics and stone cutting, were verified by means of experiments. As a direct consequence, data relative to the monitored forces revealed that better proficiencies, in terms of thrust force reduction, can be obtained with negative values of the rake angle while the effects on the cutting force can be considered almost negligible. A wide overview on the experimental tests was also given to asses the repeatability of the obtained results and to provide a clear justification in the choice of tool geometries which are often derived from practical experience.