A universal clamping assembly for a key duplicating machine is described. The clamping assembly comprises a housing having a pair of opposed flat guide rail support surfaces and a sliding tip clamp is guidingly displaceable along each of the guide rail support surfaces and are urged against the tip of the key and key blank blades which are positioned on the guide rails. A pivoting clamp is displaceably engageable on a forward top edge of the respective key blades to apply a downward force on the key blades to ensure that the lower edge of the key blades is firmly resting against the guide rail support surfaces. A pair of cam operated side clamps is actuable to further clamp the blade on their sides at two distinct areas. The universal clamping assembly is capable of accommodating different key and key blank lengths, widths and thicknesses. The method of clamping the key and key blank is also described.