So, my teenage daughter helpfully propped my Tanglewood Odyssey against a REALLY hot radiator in the house. It was there for an entire day.
Shockingly out of tune when it had cooled down, but now sounds better. What's going on?
Yep there's a number of things that can occur:
* thermal movement - each wood piece expands and contracts in line with temperature, in the extreme it can cause the wood to warp or buckle, irreparably.
* humidity movement - each wood piece expands and contract in line with humidity in the air and in the wood, unless water damaged or completely bone dry causing cracks/seperation this normally is reversible. This can be 4-8% change!
* glue joints can move / slip and sheer with extreme heat.
The effect of temperature and humidity can bend/warp woods but when they're in a guitar that expansion/contraction can cause necks to bend/bodies to bend etc. Extreme change of length etc can split the wood along the grain if there's too much difference. The good news is that typically a guitar can return back to normal but it may take some time.
What I would do is put the guitar in a normal temp room with normal humidity (possibly put a damp rag in the same room but not on the guitar). The wood will then absorb moisture from the air naturally (it may take a week or two). If it doesn't then it may need to go back to a Luther for assessment.
Acoustics do have a truss rod, but in the case of humidity change like this I would leave it for now, let the guitar rehydrate a little and then look at the situation which may mean some adjustments. As long as the neck/frets are positioned correctly (no warping or neck angle changes) then it should be adjustable back.
I have an acoustic I left in the attic (Art and Luther Cedar in a hard case) not thinking about the oven it would be come during summer. The result is the glue has separated the bridge, the scratch plate has moved and the neck has warped with a chance that either the body warped or the braces have separated from the top. I've read of people doing the same by leaving it in a car. When I have the time I will reseat the bridge (it's shifted forward) and sort out the neck), I may even have a go at the braces inside to optimise the tone (the braces seem scalloped to design and not to the unique wood response).
Making the guitars, I take it slow on purpose. I leave the wood to naturally release the stresses that can be exposed when cut. The 2.,4m plank of maple lived in our house for 3 months along with the other woods to acclimise to where they'd normally be. From that 2.4m length only about 1m remained stable and didn't warp or bend (due to grain orientation). That section became the neck though on the two guitars (along with other woods - the same approach being taken for them too). Good mass produced guitars should be more stable (choice of grain orientation, wood cut and attention to stability), but this is why I avoid new cheaply built guitars that don't tend to be as stable.
but I managed to carve part of me yesterday, so today I managed to bend ONE of the solid linings (of 8). They're thicker and so take more time. Tomorrow I'll crack on make the next three. I'll then glue those in.
