Making the back braces. Two braces are planed from one piece of timber, it’s easier to work that way because it’s wider. First, the pieces are squared up on the shooting board. Next, the braces need to be curved. Although an acoustic guitar top and back look flat, they are actually slightly domed - the top by about 3mm, the back slightly more. This allows the wood to swell and contract with changes in humidity and also imparts much greater strength to the body.