Wood Swelling? I'm baffled

[chrisdebo]

I built a mahogany(body and neck) Gibson Explorer kit in December. I took a break before completing the electronics and it hung on the wall for four months (from the headstock). Yesterday, I took it down and completed the wiring and added the strings. When I went to tighten the strings, I heard a few pops and the neck came loose. This is a fitted neck which fit great in December. After a lot of cussing and removing the old glue, the heel of the neck would not fit into the body (too wide). It's like the neck swoll up since December. This is the eighth neck I have fitted/installed and the third glue in neck and I have never come across this before. The guitar has never been outside and the only moist thing I have put on the neck is Scott's liquid gold. I took 3-4mm off the neck heel and it fits now but I would like to understand what the heck happened so it doesn't happen again.

Thanks, Chris

[mistermikev]

no expert but it sounds a lot like what happens when you build with wood that hasn't had enough time to actually dry.  wood doesn't just shrink over time... it expands and contracts to a degree that gets less and less once the wood if fully dry and I'm told it can hit a low percentage at one point but still not be ready (ie seasoned).  It has to get down to low moisture content and stay there consistently to be really considered workable.  

That said, it is entirely possible the neck pocket was just so tight when the neck was put in... that once it swelled a little bit it cracked.  Keep in mind that wood glue itself will expand the wood via moisture... however, I've done my neck joints tight enough to lift a 5lb body with just a friction fit on the tenon... and have not had issues with it cracking so I would guestimate this is not the case here. 

to completely bust a glue join... I would have to assume it wasn't a great glue join to begin with - not throwing stones at all and please don't take offense.  I've seen wood crack from expansion, but never seen anything even close to a neck popping completely out.

 

just one simpletons' observations so... mix it with others and find the center.

[Bizman62]

I took a look at the weather conditions in your whereabouts and it said it's pretty wet all year long, the winter being short and cold and the summer long and hot.

As no-one can tell how well the woods of the kit had been dried before cutting to shape, we can only look at the conditions after you bought it. If the wood was still green(ish) or the storage conditions humid it may have swollen to a tight fit in the wintery conditions when you glued it. The four months hanging on the wall with the weather becoming warmer has then dried the wood, widening the neck pocket and narrowing the heel - wood lives sideways more than length vise - and snap, crackle, pop you go.

[chrisdebo]

The popping sound was the glue breaking; the wood is intact. I was surprised at how little glue I had applied, though. I think it was a combination of that and the weather /season and the time lapse. This is my first kit with mahogany body and neck. For some reason I thought the dense wood would be less prone to issues.

Thanks again. There is no one around here who likes to luthier., so it was good chatting.

[mistermikev]

30 minutes ago, chrisdebo said:

The popping sound was the glue breaking; the wood is intact. I was surprised at how little glue I had applied, though. I think it was a combination of that and the weather /season and the time lapse. This is my first kit with mahogany body and neck. For some reason I thought the dense wood would be less prone to issues.

Thanks again. There is no one around here who likes to luthier., so it was good chatting.

this lends further credence to the idea of the issue being the glue join.  if glue is properly joined... then the wood is going to crack vs the glue.  a good glue join is stronger than the wood around it.  so your problem was not just not-enough-glue... but more an issue of solid meeting of wood on wood after being glued.

[Bizman62]

1 hour ago, chrisdebo said:

I was surprised at how little glue I had applied,

There should not be much glue in a good joint. If you get a little squeezeout all around when clamping, there's enough glue. In theory it's possible to apply too much pressure to push all of the glue out. That would be difficult on the sides, though, as there's no clamps.

I took a look at several mahoganies at the Wood Database and found out that the volumetric shrinkage can be up to 17.4% depending on the species. As you haven't told we don't know how the wood was sawn which makes it impossible to tell if it's more about radial or tangential shrinkage in your case, anyhow if the wood hasn't been thoroughly dry when glued, be it because of poor preparation or extremely moist conditions,  shrinkage may be part of the issue.

You also didn't tell what glue you used. A Titebond join is basically stronger than the wood, but urethane glue can pop cleanly off because of a shock or in your case the string pull.

[chrisdebo]

Good information. I will look at the sawn direction from now on. I always use Titebond. Thanks for edumacating me!

[Bizman62]

Hey, we're all here to learn things, either by asking questions or trying to find answers to questions posed by others.

[ADFinlayson]

I expect this will be down to change in humidity, get yourself a cheap hygrometer (mine cost about £10) and check the humidity in the room it's stored. Wood will swell in a humid environment like a damp garage as it takes on water and shrinks in your house that will be dry due to central heating. I've routed neck pockets in the garage in winter before, had a perfect fitting neck, taken it in the house and within a few hours the pocket is as loose as a well used wench.

A pocket that is too tight can starve the joint of glue as it's pushed out during fitting, so if it was humid at the time, the tiny amount of glue would not be enough to hold it together. Where as if it's very dry at the time a tight neck pocket is fitted, introducing humidity can cause the joint to shrink and the area around the neck tenon to split. 

[Ronkirn]

Wood WILL expand and contract....  that's why the subtle cracks appear in the joints in set neck guitars, 

when it swells the heel of the neck, or tenon on set necks will expand.... but the mortise, or neck pocket will get smaller as the surrounding body expands.. it only takes a little and a well fit combination are no longer compatible, requiring further "fitting".

 

r

[Bizman62]

@Ronkirn, I just had to illustrate what you said.

The brown and grey are the tight fit made in fresh wood. The red and pink represent the way wood shrinks mostly sideways when it dries. Highly exaggerated!