The invention concerns a CAD / CAM machining apparatus having an upper face and a lower face and one of the cells filled with a composite material to be machined by CAD / CAM, said material unidirectional fibers embedded in a cross-linked polymer matrix.The invention concerns a preform for a CAD/CAM machining apparatus havingan upper face and a lower face and in which at least one of the cells isfilled with acomposite material to be machined by CAD/CAM, said material comprising longunidirectional fibers embedded in a cross-linked polymer matrix.