Mending an upper bout crack in a 1960s Gibson LG1

[Barbara Millikan]

This guitar came to me with the bass side cracked and warped. There was about a 1/8 inch shift in the top on the neck side -- the entire section moved south in relation to the rest of the guitar. Unfortunately no pictures of that, but it looked a bit like the movement on the D28 Martin that Frank has up as a repair example on Frets.com. Only cracked on the one side, though and there was about an 1/8" difference in height between the lateral top and the medial part next to the neck. The crack had distorted the ivroid binding and rosette without breaking either part.The crack runs along the edge of the head block.

I humidified the guitar for about a month, checking it every few days, and gradually the distortions straightened out. Part way through, I removed just bass strings, to torsion the neck toward the treble, and then, a bit later I took the rest off.

Finally this week I applied some clamps to see if I could get the remainder of the warp in the top out. (Humidity took the lateral shift out just about entirely).

The head block has not been jacked or messed with, but it look like someone might have applied a patch some time in the past that popped off.

 

I am guessing that the guitar suffered from both low humidity and an unfortunate stay in a car in the sun. The owner said he bought it cracked, but that the shift and distortion showed up while it was stored in his room. 

I am now about to patch and glue it .I am thinking of both patching the crack next to the head block and adding a 1/8 inch x 3 inch x 4 inch trapezoidal shaped piece that would go from the head block to the brace, widening to cover the cracked area. Grain of patch to run 10 degrees or so off the grain direction of the top.

Questions:

1. Do big patches also need their edges beveled?

2. Does this patching plan sound like it solve the structural problems or am I missing something about what made the guitar do this in the first place?

3. Titebond or Hide glue?

Thanks,

Barbara

[Barbara Millikan]

Here are the photos of the guitar in its current state.

[griff]

If the crack moved 1/8 inch over time it has undoubtedly let go of the upper face brace, so first thing would be to check that with a thin pallet knife, then repair. If the crack really does run directly along the line of the headblock, no amount of cleating will secure it since there is no area to fix the cleat to the block side of the crack: you'll have to work glue into the crack (which you'll want to do regardless), and cleat the area where the crack leaves the block and runs out to the soundhole). But your pictures seem to show that it's away from the block, or this guitar has a very wide headblock.

I use two cleats in this situation, as you mentioned, though the dimensions you suggest are very large.  You should get the cleat within 1/8 of the soundhole edge. There's no real need to bevel the edges of any cleats, it just looks professional. Any cleat that abuts the edge of a brace or block shouldn't be beveled. Either glue will work, I'd use AR glue, but if you think someone will want to undo your work at some point and re-do it, use hide glue (then again, if you're unsure about hide glue, use AR). 10 degrees is too little...figure between 45 and 90.

Removing the bass side strings to torque the neck away from the crack would actually have the opposite effect of what you intended: the neck would pull up on the treble side and twist into the bass side where there is no equal force. Fortunately removing half the strings has no effect on neck angle (at least over the short term), Gibson in the 60s may get a bad rap for quality control, but they built them better than that.

 

[Barbara Millikan]

I did already check the brace; it was loose for about an inch and I glued it down with the Titebond as well as working glue into the crack and clamping the whole thing.  It is a wide head block.The crack starts about maybe 1/8 inch out and curves into the block. My reasoning in putting in that wide a patch is that it would stabilize the head block. The question is, what caused the shift in the first place?

Barbara

[Tim Mace]

A hard knock would be my guess.Under tension ..