Evaluating the use of industrial X-ray CT to the reverse engineering of bowed stringed instruments

For centuries, simple contact measuring instruments (e.g. callipers, profile and thickness gauges) have been used by violin makers for recording bi-dimensional information about their creations. Since its invention, film and digital photography have also been used to document shapes and colours. Traditionally, gypsum castings and RTM replicas are used to store information about the 3D shapes of back, bellies and scrolls. During the last 30 years the applications of non-contact systems such as X-ray computed tomography (CT), and laser and structured light scanners (LS) have opened new horizons to the bowed stringed instruments metrology. This work compares two state-of-the-art non-contact systems: an industrial X-ray computed tomography system and a Structured Light 3D scanner. Their results in terms of accuracy, repeatability and uncertainties are assessed and compared to reference tactile Coordinate Measuring Machine (CMM) measurements. Experimental results prove that, with the considered experimental set-up, CT provides better results than LS in terms of deviation from CMM reference measurements, and uncertainty.