I use this press for two things. One is to hold the parts of homemade books flat and together while their glue dries. The other is for linoleum block printing, which I don't do nearly as much as I wish I did.
I built this one out of pine 1 X 4's. The three horizonal beams are each made of four pieces laminated together. The string isn't there to hold anything together, structurally. It holds the press screw from falling down when you loosen it