Method for making perforations on a sheet or an object

The present invention relates to a method of forming perforations in a plate by forming first grooves (1) on a first surface (100a-103a) of said plate (100-103a) and second grooves (2) on a second surface (100b-103b) in such a way that the grooves on the plate are opposite to each other， at least some of the first and second grooves on different sides of the plate (1， 2) intersect and that the depth (a) of the first groove (1) and the depth (b) of the second groove (2) together are at least half the thickness (s) of the plate， whereby perforations of the plate are formed at the intersections of the first and second grooves (1， 2) (3). The invention can be applied in such a way that the first and second grooves (1， 2) are substantially the same depth and / or in such a way that the shape of the bottom of the first and / or second grooves (1， 2) is flat or convex. In one embodiment of the invention， said grooves are machined by CNC milling， surface milling or planing and the machining is controlled by CAD， CAM or some other computer program suitable for the situation.