Saw two 26 cm by 12 cm pieces of the wooden board
Saw two 12 cm by 6 cm pieces of the wooden board
Screw the small boards right angled on (the end of) the bigger boards.
Take the two leftover 10 cm pieces from step 1. Drill a 12 mm hole throughout the top of each piece. Screw them in the center of each 26 cm by 12 cm piece.
Bolt the feet supports on the drilled 12 mm holes on the base. Use spring washers, washers, hexagon nuts and threadedrods to connect the feet supports to the base.
Fill the screw holes with wood paste and sand them smooth.