Truss rods again

[Jonathan Peck]

I've had this mandolin by modern maker Michael Heiden for about a week now. The instrument is one made without a truss rod and is 4+1/2 years old. I've had this instrument out to jams twice, and have been playing it everyday. Even with the wild humidity swings going on lately, I find that it's most always in tune and stays in tune, even when playing harder in jam situations. I can't say this for any other mandolin I own, or have owned in the past. The other variable is that I have heavier gauge strings on it than I usually play with (J-75's) and have no previous experience playing with heavier strings.

Does the absence of a truss rod = a more stable mandolin? It's just an amazing thing not to have to even tweek the tuning every couple of songs. There may be other variables at work here (neck angle, bridge slightly tilted towards the tailpiece, set-up, flex in the top) as my old 'A' doesn't share this trait despite the absence of a truss rod. What do you think?

***oops, edit**
The Heiden has a non-adjustable carbon fibre truss rod

-jonathan

[amowry]

I've built 8 mandos with cf instead of trussrods, and to me the greatest benefit is the reduced weight. I haven't kept any long enough to notice if there's a difference in regular tuning, but the necks are noticeably stiffer when I first tune them up.

[ErikAitch]

***oops, edit**
The Heiden has a non-adjustable carbon fibre truss rod
That's the answer, I think.

Owing to the greater stability (and, IIRC, lower expansion compared to steel) of carbon fiber laminate, necks are much less likely to require adjustments over time, and the adjustments they do need will be smaller.

OTOH, those adjustments for relief are not nearly as easy to make. OYAH, neither should effect ease of, or stability of tuning significantly.

Hopefully obvious opinion. Corrections welcome.

[sunburst]

Does the absence of a truss rod = a more stable mandolin?
Short answer: No.

Some necks are stiffer than others because some wood is stiffer than other wood. I have a mandolin with a hard maple neck with an adjustable truss rod and no CF. I've had it for two years and the neck is still just a straight as it was when I built it, with no tension on the rod. In fact, I was hoping a little more bow would pull into the neck so that I would have room for adjustments, but the wood is so stiff that it doesn't move. If that neck had CF in it, the CF would just be along for the ride. It would not add any stability to that neck under normal circumstances.

I'm trying to finish up a mandola with a quilted big leaf maple neck. That wood isn't very stiff, so I put two strips of CF in the neck, and an adjustable truss rod. The idea is; the CF will give the neck stiffness and the adjustable rod will give it adjustability (something I value, adjustability).

So, CF in the neck can add stiffness and stability to wood that is not stiff to start with, but that's not the only thing that affects how well the mandolin stays in tune. In fact, tuning changes from humidity changes are usually because of the top of the mandolin moving and raising or lowering the bridge. When relative humidity goes up, the top will take on moisture and the arch will increase in height. When the relative humidity goes down, the top will loose moisture and the height of the arch will get lower.

So, the CF in the neck of your mandolin might be making a significant contribution to the stiffness of the neck, but not to the rest of the mandolin. I'd guess that you just lucked into a particularly stable collection of woods in the mandolin that you got, and the CF may or may not be contributing to the overall stiffness of the mandolin by adding stiffness to the neck only.

[Jonathan Peck]

Ok, well I don't have the magic mandolin after all. Humidity spiked about 15% yesterday and my mandolin responded by going slightly sharp. It would make sense that Michael might have used stiff wood for the neck. The mandolin does appear to be very stable and not affected as much as my other mandolin. Thanks

[Hans]

I would suspect the instrument went sharp from the swelling of the top rather than the neck moving. You have a rigid box with no finish inside...when the humidity goes up, the whole box swells.

[Dale Ludewig]

I'm with Hans. The humidity level acts much more quickly on the body "box" than the neck. It will swell, put slightly more tension on the strings and guess what? You've drifted sharp. There's lot's of other factors going on, perhaps as to stability on being in tune. What tuners did Michael put on that mando? From my experience, Waverleys (sp?) are really stable. Others are less so. But if your body changes 'cause of humidity changes, no tuner set can make up for that.

As an aside and another question related to this and something I've not ever understood completely, so help me my builder friends. CF stiffens the neck. I've used it and have been delighted by it. But isn't the idea that CF makes the neck virtually immovable? Then you put in an adjustable truss rod, which is what I usually use. Then you try at some point to move the neck with the truss rod against the CF. It seems like an ideal situation for stripped threads on a truss rod, or hopefully on the truss rod nut. Still, I don't get it. But then, I've never used both on the same instrument to see what would happen. Inquiring minds want to know. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/rock.gif

[sunburst]

Nothing is immovable. No solid, that is. Everything has some flex and elasticity. CF makes the neck stiffer, but not immovable.
In my experience with it, I've been able to mill fingerboards perfectly flat on necks with CF in them and had just about the right amount of bow under string tension. (That includes a Heiden mandolin, recently.)

[Jonathan Peck]

"what, tuners did Michael put on that mando? From my experience, Waverleys (sp?) are really stable. Others are less so. But if your body changes 'cause of humidity changes, no tuner set can make up for that."

Michael installed Waverlys. Overall, humidity aside, the mandolin is very starble and my brief experience with it has been that it stays in tune very well.