The machining of thin walls generally generates milling chatter, that damage surface roughness and manufacturing tools. Stability lobes which include natural frequencies are successful in case of tool chatter. When milling thin webs models are less adequate, because the interaction with the tool disrupts the behaviour of the work piece. The modal approach generally used for stability charts may be not adequate enough because of neglecting the tool and the work piece contact. This paper presents the experimental phase of a work aiming at analyse vibration modes of a thin web during machining. A finite element calculation shows the influence of a contact on natural frequencies of the part. For a better investigation, field displacements of the work piece are analysed. This work eventually aims at better knowledge of the contact between the tool and the part to improve the hardiness of models
