(weather blues) why do necks move so much. do graphite necks not move at all?

[thehangingmist]

last two weeks the bow on my neck was lowering it self quite a bit to an extent that twice i had loosen up the truss rod a tiny bit (this is a bass with a 5piece rockmaple, paduk, wenge, curly maple neck with stiffening rods inside). BUT not just my bass but i loosened up the rod on half a dozen other basses that belong to my students and friends.. every one was starting to get a slight back bow without having changed any strings or touched the setup but purely because of the weather. (May is when the weather starts to get really hot here and i usually expect the necks to get bowed on their, which is what usually happens)

today i wake up and my bass needs me to tighten that rod back up, it is hotter over the last two days than before, i cannot comment on humidity by feel as we are used to bad humid weather but am going to add a screen shot to show it varied between 20% or so to 95% in a few days. so what is to blame?

anyway now the really bad summer wave is coming along and i expect the weather to keep getting hotter and stay hot it gets up to 48C here and the humidity gets high as well. i expect the necks to need more truss rod adjustments in the favor of tightening them a quarter or half turn a couple of times if needed. when this custom bass was built, we were not expecting it to move this much. it may be moving less than other single piece maple necks but it is significant enough for me to want to set it up, i dont mind doing a set up once in a while but i hate it when i have to play and the bass feels all different. now i understand i live in a place with strong humdity changes. i wonder if graphite necks wont be effected by this? Not that i can afford one anytime now.

anyway so in your experience what effect does humidity have on the neck/truss rod adjustment? for me summers (hot and more humid) needs me to tighten the rod and winters (cold and less less humid) loosen the rod.

however when it rains, the temperature goes down but humidity goes up and that reduces the bow in the neck which tells me that it has more to with temperature than humidity. does it now?

i would love to understand how temperature effects the bow in the neck and how does humidity effect it. and then of course how does the combination of two really does all this gremlin undoing of all setups in my city.
disclaimer i think the 16-96% range is not super accurate but surely possible in a whack way it does seem too crazy for even this place 35-75% is much more of a real figure here for this time of the year and it will go upto 90 at monsoon time

 

[thehangingmist]

tagging @miziomix for research purposes

 

[Matt O]

It's the humidity and not the heat. Wood swells and shrinks as it takes on or dispels moisture due to changes in environment. When a piece of wood is "acclimated" that means that the moisture content of the wood is in equilibrium with the relative humidity of the air around it. Your neck will be stable when there is equilibrium. Reletive humidity goes up, wood will seek equilibrium and take on moisture and swell, etc.

A 16-96% swing in one week is drastic. Like, insanely drastic. I'm not surprised you are tweaking truss rods. Finishes slow this process down enormously, but they don't stop it. Im guessing an unfinished neck in your climate would be toast pretty quick.

Yes, graphite stiffeners would help prevent the neck from moving, but wooden things are going to swell and shrink no matter what in an environment that has unstable humidity like that. The best bet is to try and keep the instrument in a stable environment.

 

[Jazz Ad]

In a climate like yours, a graphite neck is a must. There is a reason why all caribbean bands use them.
Remember, the Fender bass was conceived in Cali, under a very stable climate.

 

[thehangingmist]

It's the humidity and not the heat. Wood swells and shrinks as it takes on or dispels moisture due to changes in environment. When a piece of wood is "acclimated" that means that the moisture content of the wood is in equilibrium with the relative humidity of the air around it. Your neck will be stable when there is equilibrium. Reletive humidity goes up, wood will seek equilibrium and take on moisture and swell, etc.

A 16-96% swing in one week is drastic. Like, insanely drastic. I'm not surprised you are tweaking truss rods. Finishes slow this process down enormously, but they don't stop it. Im guessing an unfinished neck in your climate would be toast pretty quick.

Yes, graphite stiffeners would help prevent the neck from moving, but wooden things are going to swell and shrink no matter what in an environment that has unstable humidity like that. The best bet is to try and keep the instrument in a stable environment.

thats great info! to look at in a cause and effect manner.. higher humidity would mean the neck bow increasing or decreasing?

to be honest i think 16-96% is exaggerated, because we would go crazy and feel insane at 96 and i would know but it might have gone there for a short while

 

[bucephylus]

As Matt O describes, the wood is responding to the humidity changes by taking up or releasing water to remain in equilibrium.

To understand the whole response, you need to first understand the truss rod interaction, because the neck is constructed with different materials. With no truss rod, the tension in the strings would cause the neck to bow outward giving high action that you could not adjust. So, the instrument makers put a truss rod in the neck (and sometimes stiffening bars) designed so that when you tighten the steel truss rod, the neck is bent backwards against the outward pull of the strings. OK

When additional moisture is absorbed by the wood in times of high humidity, the volume (and length) of the neck responds by trying to get bigger. Think of a sponge when it picks up water. But, the steel truss rod, which does not pick up water stays the same length. The overall effect is that the truss rod becomes "tightened" against the wood just by the uptake of the water. So, in times of higher humidity, we loosen our truss rods to keep the action constant. I realize you said the opposite; but, I believe if you re-evaluate you will notice what I've just stated. Then, when the air becomes less humid, the wood shrinks, effectively loosening the truss rod tension; and we compensate by tightening the truss rod to keep everything happy.

Wood actually has a very complex microstructure, which continues to undergo changes over long periods of time, even after typical kiln drying prior to the wood crafting. These changes have pronounced effects on the moisture uptake, tending to reduce the moisture uptake as the wood ages. This is just one reason older instruments are highly valued.

Graphite is a whole different animal. Graphite necks are a complex composite of graphite (carbon) fibers in a phenolic matrix. Phenolics are hydrocarbon based polymers with high thermal and structural stability (think high temperature glue). The phenolic matrix actually does take up moisture; but the structure of the polymer matrix has so much space in it that the water molecules do not change the dimension of the part as much as a wood part. So, we perceive the graphite necks as being more dimensionally stable. And, they are. Of course, graphite necks have significantly different acoustic modes; but, that's a different thread.

Hope that helps. Keep your truss rod wrench handy. Better to check often and tweak as needed. Yes, in India, I might tend to favor graphite.

 

[shawshank72]

I share your pain as i live in Canada.
This month has been hell on my necks.
3 days its cold, then its warm, then it snows, then it warms, then its cold.......
Aaaaarrrrggghhhhh

 

[Bodeanly]

I share your pain as i live in Canada.
This month has been hell on my necks.
3 days its cold, then its warm, then it snows, then it warms, then its cold.......
Aaaaarrrrggghhhhh

Same with Chicago.

Typical season: I love my bass. I hate my bass. I love my bass. I hate my bass.

 

[lz4005]

It's the humidity and not the heat.

It's the humidity and the heat. Because the way we measure humidity depends on temperature.

The reason humidity is always given as a percentage is because it's talking about the amount of water the air can hold at the current temperature.

Warm air can hold more water, so there is a lot more moisture in the air at warmer temperatures when the relative humidity percentage is the same.
50% humidity at 33 degrees is completely different than 50% humidity at 99 degrees.

 

[thehangingmist]

As Matt O describes, the wood is responding to the humidity changes by taking up or releasing water to remain in equilibrium.

To understand the whole response, you need to first understand the truss rod interaction, because the neck is constructed with different materials. With no truss rod, the tension in the strings would cause the neck to bow outward giving high action that you could not adjust. So, the instrument makers put a truss rod in the neck (and sometimes stiffening bars) designed so that when you tighten the steel truss rod, the neck is bent backwards against the outward pull of the strings. OK

When additional moisture is absorbed by the wood in times of high humidity, the volume (and length) of the neck responds by trying to get bigger. Think of a sponge when it picks up water. But, the steel truss rod, which does not pick up water stays the same length. The overall effect is that the truss rod becomes "tightened" against the wood just by the uptake of the water. So, in times of higher humidity, we loosen our truss rods to keep the action constant. I realize you said the opposite; but, I believe of you re-evaluate you will notice what I've just stated. Then, when the air becomes less humid, the wood shrinks, effectively loosening the truss rod tension; and we compensate by tightening the truss rod to keep everything happy.

Wood actually has a very complex microstructure, which continues to undergo changes over long periods of time, even after typical kiln drying prior to the wood crafting. These changes have pronounced effects on the moisture uptake, tending to reduce the moisture uptake as the wood ages. This is just one reason older instruments are highly valued.

Graphite is a whole different animal. Graphite necks are a complex composite of graphite (carbon) fibers in a phenolic matrix. Phenolics are hydrocarbon based polymers with high thermal and structural stability (think high temperature glue). The phenolic matrix actually does take up moisture; but the structure of the polymer matrix has so much space in it that the water molecules do not change the dimension of the part as much as a wood part. So, we perceive the graphite necks as being more dimensionally stable. And, they are. Of course, graphite necks have significantly different acoustic modes; but, that's a different thread.

Hope that helps. Keep your truss rod wrench handy. Better to check often and tweak as needed. Yes, in India, I might tend to favor graphite.

this is just great!! my fear is that most of my truss rods start to show some wear, i occasionally see some metal "filling" which comes back out with the wrench. often these wrenches are the one's that came with the bass and are a good fit. however some rods never show any wear and always turn very smoothly with no sign of fight but the bass that i like the most often dont turn easy and get me concerned and worked up about turning their rods as i feel i might just be slowly grinding them into uselessness

 

[thehangingmist]

It's the humidity and the heat. Because the way we measure humidity includes temperature.
Humidity percentages are all relative. That 96% is the amount of water the air can hold at the current temperature.
Warm air can hold more water, so there is a lot more moisture in the air at warmer temperatures when the relative humidity percentage is the same.
50% humidity at 33 degrees is completely different than 50% humidity at 99 degrees.

that is how i understand it!

 

[thehangingmist]

great responses guys! thank you for sharing your knowledge!

 

[warrplayer]

Graphite regularly saves my sanity several months out of every year!

 

[Matt O]

Nah.

Heat only starts to effect wood at temperatures reaching/surpassing 200F.

I could wrap a piece of wood in a damp towel and it would move, no matter the temp.

 

[arbiterusa]

however when it rains, the temperature goes down but humidity goes up and that reduces the bow in the neck which tells me that it has more to with temperature than humidity. does it now?

They are interdependent. Both matter.

As far as graphite, yeah. It doesn't move when temps or humidity changes. This was the main motivation for Rainsong's graphite acoustic guitars - which have stunning tone, by the way. But they wanted an acoustic that could be played in Hawaii. Drive five miles and you can go from some of the driest desert I've ever seen to steaming jungle. Seen what happens to high-end wooden acoustics there. Not pretty.

 

[silky smoove]

Both of my basses have Status Graphite necks on them. They are not impervious to shifts with climate changes. That said I find myself needing to do one setup every 2-3 years and it's usually a very minor tweak. I'm very happy with them, but despite some early marketing claims by manufacturers other than Status, they are not these invincible things that have superpowers.

 

[pedroims]

IME the finish has a lot to do, the neck on my classic P that has a heavy finish, I think is nitro, is very stable, the neck on my stingray that is finished with oil is very sensitive to changes in humidity.

 

[thehangingmist]

Both of my basses have Status Graphite necks on them. They are not impervious to shifts with climate changes. That said I find myself needing to do one setup every 2-3 years and it's usually a very minor tweak. I'm very happy with them, but despite some early marketing claims by manufacturers other than Status, they are not these invincible things that have superpowers.

i understand they are not magical beings that never budge.. but..
one setup every 2-3 years is amazing! did you order a status graphite neck and had a body built for those?

 

[Doner Designs]

I live in Chicago and use very high tension flats on all my basses. Currently using all Warmoth necks with steel stiffening rods and they are considerably more stable than other necks I have had. I eventually destroyed the neck on my Vintage Modified Squier Jazz bass - ran out of travel, did the washer thing, eventually the truss came through the fingerboard.

My maple necks have a gloss finish but the hardwoods (wenge and rosewood) are naked. Both are relatively stable but I still have to adjust about 4 times per year (no humidifier in my house).

 

[silky smoove]

i understand they are not magical beings that never budge.. but..
one setup every 2-3 years is amazing! did you order a status graphite neck and had a body built for those?

Yep. Status necks, Warmoth bodies. They fit together very well.