I want a small side table at my sofa. But I don't want it on top of the armrest all the time. So I kept the tabletop movable.
Step 1: Making the Base
I had a 28 mm thick and 21 cm wide board on hand. I cut a 50 cm and a 72 cm length of. I used Mortise and Tenon joinery to but them together. The mortise is 32 cm apart from one side. The Tenon is 10 cm wide. I glued and screwed it together. I added a handle on the top. Cut out with a 30 mm Forstnerbit and a Jigsaw.
Step 2: Moving Top
Next I made a mitered box with a loose fit around the post from 18 mm pine. It is 20 cm in height. The top itself is a board with 30 x 40 cm in dimension. The box is located 9 cm from the back of the top board connected with hinges.
Step 3: Finish
I put some hard wax oil on it for protection and some rubber feet. It fits perfectly my sofa.