The present disclosure relates to a 3D printer (1) for 3D printing of a construct. The 3D printer (1) has a print bed (2). The 3D printer further comprises at least one actuating tool head (3) with an extrusion element (4), wherein the extrusion element and the print bed are movable in relation to each other. The 3D printer also comprises at least one sensor (5) arranged to sense a force applied to the print bed (2) by the extrusion element (4), or vice versa. The 3D printer additionally comprises a control element (7) arranged to detect when the sensed force exceeds a predetermined value and to record a position of the print bed or extrusion element related to the detection that the predetermined value is exceeded. The present disclosure also relates to corresponding methods and computer programs.