In order to properly fix an open crack, or center-seam that stubbornly doesn’t close up enough when humidified (as was the case with this 1930 Gibson L2) I like to use a modified version of TJ_Thompson’s Top Crack Corrector Kit.
The kit is designed for Martin guitars, which are built with flat tops; but Gibsons are built with domed tops, so using TJ’s Martin-specific FLAT gluing cauls on a NOT-FLAT Gibson can cause unintended damage. However, TJ’s cleat design and repair process work really well at swelling an open crack closed and locking it in place all while keeping the crack perfectly aligned, so I devised this hack to be able to use the cleats on a radius-topped Gibson.
Photo 1. Mapping the top braces and measuring the top’s radius. The radius gauges were designed by me and are manufactured by Lewis at @eastcityguitarco (you need these if you work on Gibsons and other radius-topped guitars).
Photo 2. 12.5’ radius block roughed out. This will become the inner caul.
Photo 3 – 5. Marking and cutting the caul with the brace positions and dimensions.
Photo 6. Adding the TJ-made cleat holder and cleat stock. The stock is genius in design with its semi-cylindrical cut and double-rift grain orientation. The cleats are light and can be oriented parallel with the top’s grain without causing other issues.
Photo 7. NeoD magnets are used to locate the caul while working blindly inside the guitar. The magnets are strong enough to keep everything in place while you position the clamps.
Photo 8. All clamped up. The crack is glued and the cleats are applied simultaneously. The system is designed to be used with hide glue, which is fabulous at swelling wood and then shrinking everything tightly together.
Photos 9 and 10. The finished product. Tightly closed and level.