“…Indirect techniques, such as force, vibration, temperature and acoustic emissions, are easy to implement to correlate the sensor signals with the machine health. Researchers have used measurements of spindle motor currents, feed, forces (Nouri, Fussell, Jerard, Gao, & Linder, 2012;Saglam & Unuvar, 2003), acoustic emission (Houshmand, Kannatey-Asibu, & Herrin, 1995;Niu, Wong, Hong, & Liu, 1998;Srinivasa Pai & Ramakrishna Rao, 2002), vibrations (Berger, Minis, Harley, Rokni, & Papadopoulos, 1998;Dilma & Lister, 2000;El-Wardany, Gao, & Elbestawi, 1996), to estimate the tool wear. In contrast to the aforementioned variables, vibration is one of the features of modern mechanical machinery that is now continuously monitored in many significant applications.…”