Newbie truss rod question:

**Martyweir** · Mar-20-2007, 12:56pm

Hi All,

I'm building #1 and I am intereted in group input on truss rod designs. I'm considering the Siminoff rod vs. fabricating one similair to StewMac's traditional Rod. Not that I have any expertise or credibility on the subject, but for some reason I'm skeptical of the design of Siminoff's arched-L shaped Truss rod system. It seems like alot of the compression at the neck heel is going to come from higher up - closer to the fingerboard - which seems couterproductive to me?

To be fair I have never used or seen this system work, so I'm looking for advice and expert opinions (and maybe a physics lesson) on which system is the most effective to use.

Thanks! Marty

**Gibson A5** · Mar-20-2007, 1:52pm

Siminoff has put out a design change to his book plans and has taken the arch out of his truss rods. Go to his web site and check it out.
Bill P.

**Martyweir** · Mar-20-2007, 9:42pm

Does anybody have a link to his site where it references this? I can't seem to find it.

Thanks for the help Bill!

**Paul Hostetter** · Mar-20-2007, 10:54pm

Google, my friend.

**Steve Hinde** · Mar-21-2007, 1:54pm

I prefer using the 2 way like Cumberland Acoustic sells. Another option for you.

Steve

**Martyweir** · Mar-21-2007, 2:02pm

Not to be a wise ###, but I've been searching his site and don't see anything relating to: "Siminoff has put out a design change to his book plans and has taken the arch out of his truss rods" Got the Peg head stiffener tip, the dovetail updates, the typos, etc...

Wow, this seems to be a dead topic. Guess I'll figure it out on my own.

**Gail Hester** · Mar-21-2007, 2:15pm

Martyweir, when you buy a truss rod from Roger it comes with a drawing, installation instructions and a description and explanation of his new truss rod design. I have the sheet but don't want to publish anyone else’s material to the internet. I'm sure if you just give Roger a call he can explain or send you the information you're looking for.

**Martyweir** · Mar-21-2007, 2:34pm

Thanks Steve, I'll look at the Cumberland Acoustics option!

Hester, I wouldn't ask you to publish this. It sounds like it's proprietary (and for sale?). Bill mentioned that a retraction / correction was published (which sounds like it could confirm my suspicion) but for the life of me I can't find it online. I may call Roger and ask him for a copy of his new design. Thanks for the suggestion!

**Gibson A5** · Mar-22-2007, 10:08am

Martyweir, It was on his web page for changes to his book and I downloaded it and stuck it in my book. I went back after reading you couldn't find it (been away for a while sorry I didn't respond sooner) and looked for it. He must have removed it because his latest printing of the book must include it now with other updates. Sorry about that.
Bill P.

**Larry Simonson** · Mar-23-2007, 5:12pm

This seems to be a good thread for me to ask about the physics of truss rods. Would someone give an explanation of how they work. Thanks.

**Jim Hilburn** · Mar-24-2007, 9:55am

A compression rod in it's simplist form would be a straight rod embedded deep and down the center of the neck which is anchored at one end and adjustable on the other. In mandolins most often it's the nut in the peghead design.
It functions by compressing the neck when tightened. Looking at a cross-section of the neck at the first fret position you see it's full width with a hardwood fingerboard at the top and gets thinner, rounder and smaller at the bottom so any compression will effect that lower part of the neck first, either by the strings pulling upward at the top or the rod compressing the neck over it's length. The idea is to get an equalibrium between the string force and the rod compression so the neck stays straight or has some desirable relief (slight up-bow for playability).
If you look at a Loar style rod you see it's curved and set very low in the heel while rising to a high spot at about the 5th fret where it heads back down so the nut will be pretty far forward in the peghead. Understanding whats going on with that is a little harder to get a grasp on.
At the last Loarfest there was a panel discussion with Mike Kemnitzer, John Monteleone, Dave Harvey, Steve Gilchrist, Lynn Dudenbostel, and Roger Siminoff. I asked them about the Gibson style and there was quite a bit of differing opinions on how they work and why. Some still use this design while others have moved on to other designs they believe are more effective.

**Hans** · Mar-24-2007, 10:15am

I have used the LMI TRST rod for a very long time and find it to be the best for me. It is VERY positive working. You imbed it in the neck, and when you are ready to straighten the neck give it a few cranks. Straighten out the neck and you then can adjust it both ways. I recently did a truss rod adjustment to a 2 year old instrument that had very low action and a slight buzz on the 3rd fret, D course. Less than 1/8 turn did it.

**Dale Ludewig** · Mar-24-2007, 6:05pm

Hans, isn't there a law in Meenasota about using that title? Look out man.

**Dave Cohen** · Mar-24-2007, 8:15pm

If two guys who wouldn't know a standing wave from a traveling wave if one or the other hit them can call themselves "...(something, something) Acoustic Design", then Hans is certainly entitled in my book to call himself an acoustic engineer.

**Hans** · Mar-24-2007, 9:02pm

Well, I wouldn't know a particle wave from a tidal wave. #

**Larry Simonson** · Mar-24-2007, 9:18pm

Thanks Jim and Hans but I'm still confused, especially about the compression of the neck. Would it be correct to say that the truss rod counters to upward component the string tension puts on the neck, such that in the case of a low action, the nut on the truss rod would be backed off a bit?

You would think I would know this after 4 decades of playing truss rodded instruments. Luckily I never needed to tweek them.

**Rob Grant** · Mar-25-2007, 3:04am

Who needs a trussrod anyway (?). Three piece laminate the neck and properly orientate your grain direction or just stick a bit of carbon fibre under the fretboard. It's like this is a mandolin, not a bass guitar!

I've embedded quite a few homemade stainless rods in my early mandolin necks and never had the need to adjust them. All the rod really seems to add is weight.

**Hans** · Mar-25-2007, 5:30am

Larry, that's the basic idea, and the idea behind giving the LMI rod a few cranks to bow the neck backwards, then straighten the neck out. Gives adjustability both ways. I never did like the compression rods because they really can mash the wood in the nut pocket. Don't know if they have adjustability both ways. I've had mixed results with their ability to straighten a neck that has pulled up from string tension. I have seen them pull guitar and banjo necks into an S curve.
Sterve Smith at Cumberland Acoustic makes another kind of "dual action" T/R that adjusts both ways and works very well, I'm told.
Rob, I'm sure that no rod or stainless bars/carbon fibre work well, but they have zero adjustability. Don't want to get into what's best, as the original question was about truss rods.
Each of us has our own ideas about what works. #

**David Catalfamo** · Mar-25-2007, 8:21am

I totally agree with Rob, and this only my opinion, so please don't anyone take it personally, I can't for the life of me understand why anyone would put a truss rod in a mandolin neck. I guess if you want future problems , well then yes it would make sense. What was loar thinking?, let's plow out a channel make the neck weaker add a rod and hope when it bows under compressive tension we can tweak it back. Every builder and engineer knows when you need a beam of wood to carry a load that laminate wood has superior strength to solid wood. Now take a solid piece of wood a cut a channel into into and you are really asking for a miracle. A three piece neck or even a five piece as Gabriele Pandini uses will never ever go anywhere if done properly. Not only will you get a stronger neck but you will be using your resources more wisely.

**Jim Hilburn** · Mar-25-2007, 9:53am

Sorry La Unta, but if you make a mandolin neck with a profile anywhere close to as thin and narrow as a Loar, even with an ebony laminate and quartersawn orientation the string load can and will put relief into that neck. Wood is plyable and like I tried to point out in my first post, it is weakest at the lowest part of the back of the neck. This will stretch under pressure. Whether you think adjustability is nessesary or not you will still need some kind of re-enforcement, IF you are making a long thin Loar style neck and not some big thick honkin' club.
Pre-Loar Gibsons used re-enforcement. If you could see a cross-section of one you'd see they cut a big V-shaped channel under the fingerboard that went almost all the way across the width of the fingerboard and inlayed a piece of hard maple. Go ahead, saw one in half and look. That combined with the fact that they have wider fingerboards and are very short and stout meant they have for the most part held up well for 100 years.
But when they engineered the Loar, they wanted a slim narrow neck and with the 15th fret joint they knew they needed something to counter the strings. There was no carbon fiber or graphite so counter-acting the string load as opposed to trying to build in the strength to oppose it was a good choice and has proved to be a very effective way of dealing with the problem.
You do have other choices today and I don't defend the trussrod over re-enforcement, I'm just trying to explain what it's about.

**sunburst** · Mar-25-2007, 10:32am

It's also about adjustability. Not every string set and not every player likes or needs the same amount of relief in the fingerboard. A neck, rigidly assembled and reinforced into a one-size-fits-all amount of relief, isn't for everybody.
Every solid material has some elasticity. Every builder and engineer knows that no neck, regardless of construction, is completely unaffected by string tension. Many builders stiffen with CF and add the adjustability of a truss rod also. I do that myself with softer neck woods, but have found no need for stiffening hard maple mandolin necks that have adjustable rods.
Any engineer also knows that material removed from the neutral, central part of a beam (neck) has much less affect on the stiffness and strength of the beam than removal of wood from nearer either edge of the beam. When one excavates for a truss rod, the back of the neck is still there, and the fingerboard is then applied, so that the edges of the beam are undisturbed; the fingerboard being one edge, and the back of the neck being the other. After the rod is installed, a filler stick; another beam; is glued (laminated) into the cavity above the rod. There's not a huge loss of strength or stiffness, especially when hide glue or an adhesive that doesn't creep is used in the construction. (Glues and adhesives that resist creep (plastic deformation) resist sheer, and help preserve the stiffness and shape of the neck.) A neck with an adjustable rod is, in fact, a laminated beam.

So one reason some of us builders decide to put an adjustable truss rod in our mandolin necks is because many customers like an adjustable neck, and our customers are where our $$ comes from, and $$ is what we live on. Furthermore, as a repair person as well as a builder, I can say that I, personally, as a repairman, prefer an adjustable neck to one that is stiffly and rigidly built in the wrong position for the taste of the customer and for me as the one setting up the instrument.

**Hans** · Mar-25-2007, 11:22am

Thanks John, Jim...I don't know how many times we have to say it: "ADJUSTABILITY"! Get it? Jeez...
If I were to have had a CF or steel rod in the instrument I was talking about, raising action would have been the answer, but the customer didn't want the action raised (action was 3/64" on the G course and 1/32+" on the E course). Next alternative would have been to dress the frets...lot easier to just tweek the T/R.

**Jim Hilburn** · Mar-26-2007, 8:24am

This is from Adrian Minarovic's Loar plan and used with his permission.
I've heard it said by some that this design is counter-productive in that as tension is applied the rod will try to straighten itself and cause the opposite of the desired effect. But on the other hand I remember Charlie Derrington saying how effective they are. Is it because of the extreme curve that the force is between the two nuts at each end and that forces the top of the curve upward and thus pulls the front of the neck downward? Or maybe it's just locked between the high spot of the arch and the low angle in the peghead and is only working on the front half of the neck. As I said, it didn't seem the panel of experts in Bakersfield were all exactly sure how it worked or convinced it worked either.
I've never really made one exactly in this shape in the neck because I've only recently had these plans and that's a difficult slot to make. I'm also using a completely different design.
Anyone care to add their 2 cents?

**sunburst** · Mar-26-2007, 8:58am

I don't know how or why those work.
I do know that a straight adjustable rod, set as close as practical to the back of the neck works, so I'm sticking with it.

My assumption, with those curved rods, is that the rod does, in fact, 'try' to straighten out when you tighten it, but it also compresses the back of the neck, and, if you're lucky, the compression of the back of the neck wins out over the rod 'trying' to straighten, and the rod adjusts the neck as you would expect.