2-way truss rod and humidity changes

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pbd
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2-way truss rod and humidity changes

Postby pbd » Tue Dec 04, 2018 5:58 am

I've long been used to the behavior of the regular one-way truss rod where when it gets more humid, the wood expands, the truss rod gets tighter, and the neck gets flatter (less relief) -- and the opposite when it gets drier, so that you generally have to tighten the truss rod in the dry winter and loosen it in the humid summer (here in the northeast USA).

But with my B50 fretless bass (built from the kit 2 years ago -- awesome, BTW) which I understand has a 2-way truss rod, I've been experiencing the opposite behavior! I've had to tighten the truss rod in the humid summer and loosen it in the dry winter.

Is this normal and what you would expect? What are the mechanics involved that would make it behave this way?


Thanks,
Peter

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spudmunkey
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Re: 2-way truss rod and humidity changes

Postby spudmunkey » Tue Dec 04, 2018 8:20 am

Is your fretboard nourished enough? I suppose it's possible the fretboard is moving more than the neck wood. If it's the wood that's moving, it would cause it to exhibit "backwards" movement compared to if it were the neck wood. :think:

pbd
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Re: 2-way truss rod and humidity changes

Postby pbd » Tue Dec 04, 2018 7:43 pm

That is a good point and an interesting idea. I suppose if the fingerboard moved more with humidity changes relative to the neck wood it might cause this backward motion (still not quite sure how). When I finished this neck, I applied several coats of tung oil to the back of the neck but kept it off the fingerboard. I don't think I've applied anything to the fingerboard since then. I'll apply some lemon oil now -- probably should have been doing that all along.

BTW, this is a maple neck with two walnut stripes.


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