Sander machine for machining at least one panel or workpiece, said panel or workpiece comprising a first surface which is substantially flat and a second surface, which is shaped, opposite said first surface, said sander machine comprising: first moving means for moving, in use, said at least one panel or workpiece to an operative zone according to an advancing direction; sanding means placed at said operative zone and configured to sand, in use, said first surface of said at least one panel or workpiece; an abutment member which is movable according to an axis being transversal to said advancing direction and placed above said sanding means such that when said at least one panel or workpiece advance according to said advancing direction, said at least one panel or workpiece pass through the space comprised between said sanding means and said abutment member with said first surface facing said sanding means and with said second surface facing said abutment member; and actuating means for moving said abutment member along said axis; wherein the sander machine is characterised in that it comprises: a control unit which is configured to know advancing speed and/or position of said at least one panel or workpiece along said advancing direction and the profile of said at least one panel or workpiece according to said axis, which at any moments is between said sanding means and said abutment member when said at least one panel or workpiece advance along said advancing direction; said control unit being operatively connected with said actuating means such that said control unit controls, by said actuating means, the movement of said abutment member along said axis based on the advancing speed and/or the position of said at least one panel or workpiece along said advancing direction, the value of said profile, such as to allow said sanding means to sand, in use, said first surface in such a way as to achieve a higher planarity level of the first surface. first moving means for moving, in use, said at least one panel or workpiece to an operative zone according to an advancing direction; sanding means placed at said operative zone and configured to sand, in use, said first surface of said at least one panel or workpiece; an abutment member which is movable according to an axis being transversal to said advancing direction and placed above said sanding means such that when said at least one panel or workpiece advance according to said advancing direction, said at least one panel or workpiece pass through the space comprised between said sanding means and said abutment member with said first surface facing said sanding means and with said second surface facing said abutment member; and actuating means for moving said abutment member along said axis; wherein the sander machine is characterised in that it comprises: a control unit which is configured to know advancing speed and/or position of said at least one panel or workpiece along said advancing direction and the profile of said at least one panel or workpiece according to said axis, which at any moments is between said sanding means and said abutment member when said at least one panel or workpiece advance along said advancing direction; said control unit being operatively connected with said actuating means such that said control unit controls, by said actuating means, the movement of said abutment member along said axis based on the advancing speed and/or the position of said at least one panel or workpiece along said advancing direction, the value of said profile, such as to allow said sanding means to sand, in use, said first surface in such a way as to achieve a higher planarity level of the first surface.