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I think the most interesting old Martin rod was their 3/8"x3/8" hollow steel tube -- much stiffer than a T-bar or U-channel in torsion. But maybe twist-warped necks are so rare that's not important?

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David Malicky

Yessir, the tube is stiffer in torsion, but the T bar was stiffer where it counts, and also left much more wood for carving. We typically see more relief issues with the square tube Martins than we do with the T bar models, though many of us feel that the real culprit is that they appear to have glued the tube into the neck simply with PVA(Titebond?) glues, where the T bars were fixed with HHG. Same with the fretboard; PVA VS HHG, meaning that the PVA glued-up necks can cold creep where HHG won't.

These days, I use a thin-wall 1/2" square steel tube for guitars, but for mandolins, I have to use a 3/8" tube, since a 1/2" tube won't allow the carving of a typical mandolin neck; the T bar was especially ideal for mandolins...! All glued into a tight-fitting channel with poly glue(zero creep).

Mario, for the uninitiated amongst us, could you post a pic of the t-bar you're referencing?

Steve

Thanks, Mario--interesting. How much flex relief do you get with the 1/2" steel tube?

Using some info on the T bar... http://theunofficialmartinguitarforum.y ... pic/137207 http://theunofficialmartinguitarforum.y ... ock?page=2 ...
for the 0.5" tall version, I get a moment of inertia of .0019 in4, which is indeed a bit heftier than the 3/8" tube (I assume it's 0.065" wall), at .0013 in4. The 1/2" tube comes in at 0.0036 in4.

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David Malicky

Twist is quite rare in mahogany necks, and is usually because a bad piece of wood was used.
I have used the aluminum channel Martin style rods since the mid-1980's, and I have yet to have a problem.
For years, my main complaint with two-way rods has been that they are too sensitive. Having left-hand threads on one end doubles the reaction to a given input. That problem has been solved with the Allied style of two-way rod, which uses right-hand threads on both ends.....coarse thread on one end, fine on the other. That makes the reaction very slow, which IMHO is preferable. The two-way rod is a bit trickier to install, because the rod attached to the adjusting nut must be free to turn.
The beauty of the tee bar is that it is held in place by the thin top web. Unlike the square tube, that shallow channel does not change dimension much at all under changing moisture conditions. If the channel is closely fitted, the tee bar cannot move, even without glue.

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John

One trouble I have with 2 way rods is that its harder to tell which way the neck is going when adjusting it. You have to have a straight edge on your neck at all times when adjusting a 2 way rod, so that you know which way its going. I had times where I almost damaged customer's guitar just because of 2 way rods...

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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

Yessir, we all have opinions and have a right to state them.

But I'll still argue against your assessment that " those preferring T bar and one-way are likely in the minority". While those who prefer solid, non-adjustable necks are indeed a minority, I suspect the majority of luthiers and manufacturers still prefer and use one-way rods, and most players really don't care one way or the other, as long as the instrument plays well.

If I was building a guitar with a truss rod,
I would make a one way.
3/16" rod that I thread.
Done a few that way,
with no problems.
Some players are WAY pickier than others,
about string action.

If I was building a guitar with a truss rod,
I would make a one way.
3/16" rod that I thread.
Done a few that way,
with no problems.
Some players are WAY pickier than others,
about string action.

Dang double post!!!!!!!!!

If it wasn't for the internet we could just build guitars the way we want to. My client base isn't very big (53 guitars) but most don't care. I do get alot of emails asking all kinds of questions, including truss rod/ neck reinforcement questions. I suspect alot of these people will never buy a guitar from any of us, but just have too much time to send e-mails. I've had 2 clients (3 guitars) who requested non adjustable necks, and another 5 or so who requested double adjustable truss rods. Most don't mention it. Usually if they don't ask, I don't go into it with them.

Grumpy, I believe I understand some (maybe enough) of how you build your necks/fingerboards. IE, pre fret, flatten fretted board (by bowing it, until it sits flat with nothing holding it, ect). Use "good" adhesive and clamping practices ect. My question is, is there any neck relief on the completed guitar, before stringing it up?

FWIW, I'm not here to argue with anyone. I'm just curious.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

With an adjustable rod, my goal is to have a dead straight neck before the string tension is applied. If that is the case, then a one-way rod works just fine.
I learned a long time ago that gluing the fingerboard on with water-containing wood glue will tend the back-bow the neck, so I always use a convex curved caul against the fingerboard when gluing it on. About 1/32" of curve is enough to create a straight neck after the fingerboard is glued on.

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John

Some interesting stuff here. It seems to me that guitar parts are a lot like fishing tackle, and it's been my experience that most of the "new and improved" lures catch more fishermen than fish.

The reports in other threads (here on OLF), of 2-way rod failures doesn't leave me with enough of a sense of confidence to want to try them any time soon, particulary in light of comments made above.

Gotoh has discontinued their 2-way truss rods. I wonder why?

Grumpy, I believe I understand some (maybe enough) of how you build your necks/fingerboards. IE, pre fret, flatten fretted board (by bowing it, until it sits flat with nothing holding it, ect). Use "good" adhesive and clamping practices ect. My question is, is there any neck relief on the completed guitar, before stringing it up?

You have it all correct, and to answer the final question, zero. No relief, like John also said. When strung-up, it will pull a few thou of relief, and if it pulls more than that, I can use the rod, otherwise, it's just finger-tight.

The big change-maker for me was switching to epoxy for gluing the fretboard to the neck. That eliminates the moisture-induced backbow the Titebond, HHG, and such creates, so it eliminates the need for a bowed caul like John uses. I used to use one, too, but it seemed like every neck was a bit different in how it responded to the fretboard being glued-on, so it was always a guessing game. Epoxy eliminated ALL the variables. And for all of you who are reaching for the keyboard to scold me for using epoxy on an item that might need removal or replacement, I've tested just about every epoxy usable on wood, and ALL release at, or slightly lower than the same temperatures that Titebond type glues release at. Much easier to disassemble than HHG, by a long shot! creep can be an issue, so use a high quality epoxy, and "tooth" both the neck and the fretboard. Epoxy is the only adhesive that benefits for toothed surfaces.

My neck construction methods have been an evolutionary method of what works and what hasn't for me. My first guitars either had heavy-wall 1/2" square tube or homebuilt T bar non-adjustable necks. With then, the PVA glues that I was using induced a wee bit of backbow that the strings pulled taught, to a wee bit of relief. Perfect! When I started to send guitars to other countries and climates, I went with a 2-way rod(see previous post) to hopefully eliminate any later issues. instead, it created some.... Luckily before the first failure, I realized those rods were garbage and changed to the aluminum one-way system(thereby saving my a$$, because by the time of the first failure, had I continued to use them I would have been looking to replace dozens!) and then soon after that realized that epoxy eliminated the need for a curved clamping caul, too. I've always pre-fretted and re-flattened the fretboards before fixing them to the neck; it just made sense to do so. Still does....

I agree with toothed surfaces for epoxy as I have done that for years with various materials but have not yet used it to glue up a fretboard. I am curious to what degree you tooth the surfaces of your fretboards and necks - sand with low grit sandpaper, score, or ??

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Steve Smith
"Music is what feelings sound like"

Some National guitars are just the oppposite.

Kent

I am curious to what degree you tooth the surfaces of your fretboards and necks - sand with low grit sandpaper, score, or ??

I ground the end of a single-cut file such that the "teeth" are now exposed. I hold the end of the file at an angle, and pull it along the surface, cutting clean, deep 'grooves'. StewMac sells a tool to do the same.

National has their own rule......Rightie loosie, lefty tightie.

Well, its hard to know which is which, some guitars turn one way, and other guitars turn the opposite way. Customers can bring all sorts of guitar and the longer you do this, the weirder things can get. Best way for me is to have a straight edge and turn the rod slowly to see which way it goes.

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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

How about for 12 fret guitars? Seems the StewMac Martin style rod is too long?