Abstract: There is described a device for a remote controlled, submarine machining unit arranged for machining of a surface on an installation element by rotation and axial displacement of a tool head and also displacement of one or more cutter holders relative to the tool head, the machining unit being provided with means for releasable mounting of the machining unit at or on the installation element, wherein the tool head is fastened in a rotor shaft axially displaceably supported in a frame and axially rigidly supported in a primary adjustment works enclosing an end portion of the rotor shaft; and a secondary adjustment works is connected to the rotor shaft and comprises means arranged for transfer of a rotary movement of an adjustment handle projecting from the rotor shaft end portion, to a displacement of the cutter holders.