28 have one end connected to the machine frame 4 and the other end connected to the stripping plate 15 fig4 illustrates an embodiment wherein the relative movement between the side plates 10 and the stripping plate 15 is measured directly in order to detect the milling depth of the milling track 17 to achieve this elements 38 40 of the measuring means 16 are provided e g at the side plates 10 and opposite thereto at the stripping plate 15 which elements allow for the detection of the relative displacement of the stripping plate 15 with respect to the side plates 10 this displacement corresponds to the milling depth s in fig4 for example such a measuring means which measures relative displacements may be formed by an optical system e g by reading a scale with an optical sensor or by an electromagnetic or inductive system as an alternative and as illustrated in fig5 the relative position sensing system between the side plates 10 and the stripping plate 15 may also be formed by a cable line 22 in combination with a cable line sensor 21 the cable line 22 is coupled with the stripping plate 15 of the stripping means 14 on the one hand and on the other hand with at least one of the side plates 10 via a guide roller 35 so that the signal from the cable line sensor 21 can immediately indicate the value of the current milling depth the side plates 10 themselves can be used as first sensor means by monitoring their position with respect to the machine frame 4 or the second sensor means by means of a cable line and a cable line sensor or by means of piston cylinder.