Repairing the braces on this Es-125 is fairly straight forward but it is a bit like building a ship in a bottle. The clean the underside of the top I used rare earth magnets with sandpaper. Moving a magnet on the topside of the guitar moves the magnet with sandpaper inside the guitar which removes the old glue and exposes clean wood for regluing the braces. Similarly, I used sandpaper stuck to a stick to remove the old glue from the braces.
The most important part of the process is making a caul to preserve, and in some cases recreate the top arch. If an archtop is strung and played with loose braces the top can sink inward causing very low action or an abnormally high bridge setting. If the braces are glued to the top without a caul they will conform to the new arch which is not functional. To make the caul I use the back of the guitar as a guide and bandsaw the caul to match the curve.
At this point it is just a matter of applying glue, aligning the brace, and having a plan to get as many clamps in place as possible.