The central section of the top and fingerboard extension on this Gibson LG-3 have come loose from the upper flat brace and upper transverse brace allowing the top section to migrate into the soundhole. The problem had occurred before as evidenced by the previous spline repair.

Given the amount the neck block had moved, I felt like removing the neck would be my best option.

By reversing a hand clamp I was able to push the neck block back into position by pushing against the tail block. This could also be accomplised with a turnbuckle or jack. With the clamping pressure from the inside I had easy access to the kerfing and binding around the neck block to clean and reglue what I could at this stage.

I then used a 3d printed dovetail and caul (with a wood backer) to hold it in position while I removed the clamp and extension block. This allowed free access to reglue the braces with the neck block in correct alignment. The dovetail and caul are 1” thick and sit just below the binding channel to pull the block forward.

I used a 3d printer to generate the dovetail and caul used in this repair but these could also be made of wood. The caul was generated by tracing the back on paper and scanning on a flatbed scanner. This could have been easily done with a careful cut on the bandsaw. I used a couple of thick pieces of cork to cushion the shoulders and add a space between the caul and the body.

With everything cleaned up I then glued in the upper flat brace and the upper transverse brace. 

Using the rosette circle as a guide I then glued in the central section of the soundboard.

With the everything back in place I used the milling machine to cut straight spline channels on either side of the neck extension and inserted splines. I had to do a little support on the inside where there were some missing pieces around the soundhole.

With a little cleanup and minor neck adjustment everything went back together.