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Same here.

Here's the break


Here I've routed off the old fretboard but haven't removed the truss rod yet. You can see the difference in length between the Hot Rod and the Allied truss rod. The way I installed it, the Hot Rod was putting maximum force on the weakest point in the neck. Also, the two 1/4" CF tubes made the neck stiffer as I wanted but was a disadvantage when adjusting the relief. After the repair the Allied truss rod went into the volute area which provided a lot more strength for the truss rod to push on during adjustment.

Fixed the break with CF, reinforced the channel, changed the truss rod, put on the new fretboard, and then brushed on EM 6000.

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Steve Smith
"Music is what feelings sound like"

I don't think that CF is a contributing factor to this problem. I use a pair of .125x.325" pultruded graphite bars on either side of the truss rod. These are buried under a filler strip. If anything, having the CF should allow one to have the truss rod do less of the heavy lifting. I'm inclined to believe that these are either wood anomalies or necks that were too thin for this rod. Fillipo's example makes me lean toward wood anomalies, since the neck was within normal specs, albeit on the thinner side for an acoustic. Just for contrast, the Cumpiano truss rod requires a 15/32" slot (these are the LMI dimensions -- his own site specifies a .5" slot. This is the same style truss rod used in Froggy Bottom Guitars. Again, if blowout is an issue, I'm guessing its a wood issue and perhaps combined with a depth issue. For reference purposes, Taylor necks are .840" at the first fret. Goodalls are .860", Ryans are shallower, I think somewhere around .8" (?). Perhaps there is a peculiarity of how this particular rod behaves where it puts more stress on the blocks, but I can't think through how.

I believe the major factor with mine was that I thinned the neck out too much when I profiled it and the depth was only about 0.100", also, the neck is eastern black walnut, and the truss rod block was pushing on the weakest part of the neck. CF just seemed to be a contributing factor only because it stiffens up the neck but I see your point, the CF may have actually been helping to push the neck back into position.

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Steve Smith
"Music is what feelings sound like"

I think that's where your problem lies. If you could have just position the rod so that the brass block would be right under the neck volute, you would have been ok.

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Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

That's one of the reasons I went to the Allied rod. It is longer so that the end is now over the volute.

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Steve Smith
"Music is what feelings sound like"

FWIW, my 2 problem necks looked identical to Steve's. 1st fret thickness was never under 21mm (about .825"), fretboard at .250" max. Aside from going to Allied rods and thinner fretboards I've also started using the headstock adjustment approach more often than not. While it's a bit more work, I sure find it a lot easier to adjust than through the soundhole. Anybody need some Hotrods?

Building the neck so that string tension pulls it to the desired relief without a lot of tension on the rod.

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http://www.chassonguitars.com

Anyone ever proactively reinforce the nut end of the truss rod channel to help prevent a blowout?

I do like the Martin style truss rods, its not too deep.

The only con about them is that they are very heavy! I was fitting a truss rod to a Stella type 12 string for it and the truss rod weights almost as much as the neck itself, but this is a very light weight neck (not including the fingerboard). The truss rod also requires a wider route, around .450 or so, but that is a less of a problem than a truss rod that is too deep, and as far as the depth is concerned, its shallower than possibly even the Allied truss rod and due to its construction, it's impossible to break them. On a modern self made steel string guitar it's not too bad assuming I don't use Sapele (too dense) but I did have issues with the neck being too heavy.

I think Stewmac offers a similar truss rod that has a U channel made from aluminum that weights a lot less than steel.

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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

I ordered some truss rods from Martin, came in today: https://www.martinguitar.com/kits-parts ... l?sef=hcfp

These are frankly the best truss rods I've ever seen. They're strong, and they're well wrapped. I don't think there's any way these things are going to ever rattle in the slot, and the slot doesn't need to be huge. And they were relatively CHEAP in price compared to even the least expensive inferior rods I've seen (and purchased!).

Frankly, I'm surprised that Martin sells them to dudes like me. In fact, I'm surprised Martin encourages amateur and professional lutherie outside of Martin the way they do.

My opinion of the company, which was high to begin with, has ratcheted up a notch.

Too bad they don't make 18 inch long electric truss rods, or bass guitar rods either.

Thanks to all the guys reccomending these rods, I would have been hesitant to buy them otherwise, considering the low price.

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Old growth, shmold growth!

I have the tiniest bit of backbow after string tension...so that's about perfect then. I have to apply a slight amount of forward pressure which takes up slack in the truss rod. Not that I planned this...I just got lucky...but since I can consistently make these necks, they all do pretty much the exact same thing.

I guess when I make thinner necks I'll get slightly more backbow unless I make my fret slots a tad wider.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Can you post a picture of that Martin truss rod you're talking about? The martin site didn't have a clear picture of it. Is it a truss rod with a U shaped steel with a steel rod inside?

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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

Wouldn't a single action truss rod be better for a thin neck?
Another thought would be to make a thumbstop that was closer to the first fret.
It might get in the way,
but it might not.

Ya...I was trying to make that very point. I like the wire I'm using so that's going to remain a constant. Using the cnc, making accurate changes to the fretslot width is pretty easy. The narrower the groove for a given tang width, the more pressure will be applied to backbow the neck. That results in a slightly convex fretboard....not concave. Once having sanded a fretboard flat, installing the frets could only create a convex fretborad. I'm not being pedantic...just making sure we're on the same page.



It's almost nothing so I have to imagine the groove was either paper thin to blow out like that....or perhaps it got glued in there oddly and the action wasn't as free as it should have been. It's kind of hard to imagine a .005" movement requiring any kind of serious pressure of the truss rod to overcome. So...I'm kind of leaning towards the notion that if that area where it popped out wasn't PAPER thin...there's a good chance the rod wasn't free and was applying a highly localized load on that spot...idk.

I hate mentioning the cnc too much because relatively few builders have them...but I'll mention this because after 17 necks with the HotRods I've been problem free and there might be something that someone can take out of it.

When I cut truss rod grooves using the cnc I can program accurate, variable widths along the groove. The brass end pieces have their own width and the rod itself has a slightly different width. The idea is to fit the rod into the the groove so that there is a slight press fit of the rod into the groove and a much harder press fit of the end pieces into their areas of the groove. In this way...the end pieces are quite secure and the rods, secure enough to eliminate the possibility of rattling, will still have free action.

The only other thing that can foul up the action of the truss rod is glue...so when cutting the final gluing surface of the neck, I program and cut a slight recess along the top of the truss rod groove... to accommodate the width and thickness of a strip of masking tape. The tape blocks epoxy ingress into the groove when gluing on the fretboard.

The whole idea is that by the end of this effort I'll have a very consistent process controlling the neck assemblies to the final point of being able to control the amount of backbow by slightly adjusting the fret slot width. So far, it's clear that my choice of fretboard and neck woods will always be a variable but I'm actually dialing in a list of numbers for that now.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

I'm not Stuart but tang width, slot width, and FB density all play a role and density is the one that's pretty hard to account for. That's why I pre-fret. You can fret the board and flatten it out before glueing and remove that variable. Since I started pre-fretting, doing most of my neck shaping before glueing the FB, and using glue with no water in it, my necks nave been remarkably consistent.

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http://www.chassonguitars.com

I have a question for everyone who use the double action rods. How do you cut your slots? Dado saw or router bit? One of the guild publications had an article by Ervin Somogyi I had read about a mistake he made using a dado blade since many of them don't cut exactly flat slots instead they cut dog ears in the corners to aid tighter joint for cabinet making. This can extend the slot enough that it can make a blow out while final shaping or sanding or under stress down the road. The photo shows what I'm talking about the dog ears. It doesn't seem like much but when we are talking about a double action rod it could mean problems at the top of the neck. A router can cut a flatter slot but it's not as easy and convenient as a dado blade..Mike

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Another day, another dollar.

The ones I got are double action, and the way I like them too, with the flat stock on top and round stock on the bottom of the rod.
They seem welded together really well and seem to be made of strong metal. The adjustment nut has some kind of round metal sheath around it which I haven't seen before. It's shrink wrapped in some kind of thin strong plastic shrink wrap. They don't look like they'll require a huge route although the adjustment nut is wider than the rod itself. Looks like I'll need to use two different size router bits with this one, not a problem.



Before I got my Martin rods, I was using the LMI double rods. I was filing the square collars round, and using a round bottom router bit.

The Martin rods are already round, so no filing necessary, I just need the right size round bottom router bit for the adjustment nut portion of the rod.

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Old growth, shmold growth!

I cut my trussrod slots on the table saw with a Diablo 7 1/4" blade. I clean it up with a chisel. The slot on the neck that blew out I cut on a milling machine.

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Steve Smith
"Music is what feelings sound like"

I leave the 1/8" kerf blade in and make 3 cuts, 1/16" apart. With an ATB blade, the overlapping cuts flattens the slot bottom pretty well. Or very well with a raker tooth. A DRO on the fence gives tight control on slot width.

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David Malicky