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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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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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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