truss rod install

[Martian]

I have been using stew macs truss rods . witht he barrel on the end, they install with just a flat channel/. I am trying a LMI TR, and am curios , I see a lot of prints where the channel has a belly in it. and have seen some vids on how to cut this. Is that a better system? Then the flat or is it just another way? thanks

[Martian]

single action. just a piece of rod with a bend

[HoGo]

single action. just a piece of rod with a bend

Simple vintage Gibson style bend. Important is how deep the line connecting the anchors is. And aslo position of the headstock-side nut - you don't want it in the thinnest part of throat but higher up the headstock which is easy with this config.
I modified this somewhat and cut straight channel as deep as possible and drill angled hole from center of heel end to meet the channel and slightly deepen the channel with small scraper on the headstock end. I shape the rod to fit. Works just like the old one without need for jig.

[j. condino]

We just had this conversation in depth about a month ago; the search engine will pull up hundreds of threads about it.....

About a decade ago, I was struggling with some truss rod issues. I contacted ten of the best builders in the world asking for opinions. I got about 23 completely different responses- single, double, up, down, straight. That lead to more confusion, so:

I made ten different necks with ten different truss rods and bench tested every one. Guess what??????? They all worked almost identical. I now use the one that fits my building process the best- single action, straight channel, with the exception that I fabricate my own from titanium.

[Martian]

when I say with a bend, I mean the rod looks like a long allen wrench . It is straight, but I am considering doing an arch in the rod like Adrians example. Just looking for pros and cons. and or, those who do , how do you go about cutting the arch in the neck? thanks

[j. condino]

The only truss rods I've had to replace were made by other folks and they broke at that right angle bend. In addition to the breaks, they can potentially cause some strange loading of the tension on the neck.

[Richard500]

Re, bent rods and fractures. Maybe doesn’t have to be repeated, but steels that are hardened for higher tensile strength also do not take bending. As I imagine that the total tension in a truss rod is comparable to the string tension it opposes, you don’t need a high-strength rod unless it’s very, very much thinner than usual. So, if you’re making your own from steel or brass, and focusing on that L-bend, make a test couple of bends in scrap first to see if there’s fracturing, and torch anneal if you still want to use the material. (Annealing is backwards for brasses vs. steels!).
I’m not building any mandolins, but on general principles I’d run a truss all the way into the instrument body in a straight line or constant-radius curve for future repair or replacement purposes. Might help hold the neck on.

[Rob Roy]

Of the 5 mandolins I've built, none have needed much tension at all on the truss rod (and I keep my relief < 0.004") so I doubt the type would make a lot of difference.