Official Luthiers Forum!

I've been away a while.... hi again. I've been focused on a project.

I'm hoping to get a list of the most reliable, trusted two-way acting truss rods used by builders.

I know of several...but I hope to see a consensus develop....and maybe read of certain rods I hadn't considered.

Establishing a minimum strength can be done easily by knowing the alloy of a rod and then doing a simple calculation to determine the cross sectional area of the minor thread diameter on the threaded rod. Assuming a good weld...the minor thread diameter will be the weakest point of a typical rod. For instance....I know of one rod with a good reputation that will break at 975 lbs of tension. That's a good minimum specification then. I'm developing mine to break at about 2400 lbs. I'm not quite there yet....but pretty close.

Thanks for your responses.

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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

Is price point important?

Of the rods I'm comparing to? Not sure I understand you.

The more expensive the other rod....the better. If I can actually pull this off and develop something as strong as I think I can...comparing it to a more expensive truss rod will better for me I suppose.

I've already proven the strength of parts of the rod. I'm sneaking up to the point of being 2.5 times stronger with geometry revisions. It's a process.

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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 like the Blanchard. The new Martin design seems pretty good too. I had welds break on the older Allied two way rods.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

I've been liking the newer Martin 2-way rods.

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Steve Smith
"Music is what feelings sound like"

Thanks guys.

Mark Blanchard has a very good reputation...a good one to emulate. I know the alloy of that truss rod. It helps a lot to know the breaking point of something with a good reputation.

I've heard the Martin recommend by another luthier I respect.

Any others?

_________________
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

Blanchard.

Blanchard

Stuart, good to see you again.
Have you seen Kevin Ryan's? It's pretty stout. As far as I know he has the specifically made for him.
How did you decide on a break strength of 2400 Lbs and under what loading conditions? Just curious.
Anyway once again, it's good to see you back.

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Jim Watts
http://jameswattsguitars.com

Thanks Jim,

Yes, Kevin sent me one to digitize in case I wanted to make that one molding it out of carbon fiber. That rod, however, uses Mark Blanchard's patented idea (thread differential on each end of the actuating rod) and I didn't want to market anything while "borrowing" Mr. Blanchard's idea or paying a licensee fee or royalty. I'm in the process of patenting aspects of mine now and, depending on what they allow at the USPTO, I may be able to make that type of rod using my patented ideas without violating Mr. Blanchards patent.

The 2400 lbs (in tension) is based on the fact that the actuating threads (#10 - 24 - Grade 8 - hardened steel) on mine will break at 2385 lbs. The minor thread diameter is the breaking point. That's about 2.5 times the strength of pretty much all the other alloys used for truss rods. Those alloys have to be machinable, weldable, and inexpensive. That narrows it down quite a bit. Truly, I only need to know ONE alloy from ONE dependable rod to have a good baseline....and I have that. I'm just looking for well respected products to test against at this point.

I've already tested to destruction aspects of the composite structure with a load cell. This will be shown on video when the thing is finished along with other testing. You'll be able to see the breaking values on the display. The funnest part of making things is breaking them....btw.

Uni-directional carbon fiber pre-preg is used in a compression molding process. I'm trying to refine the design so that the bolt is the weakest part of the structure. The main part of each rod will take 13,000 lbs. in tension...so that isn't an issue, either in tension or compression...but the places where the two rods connect are more challenging and require some pretty specific engineering to get them out past 3000 lbs in tension or compression. It's a TIGHT little area requiring specific fiber orientation to carry that much load. It's a design challenge but it's a repetitive molding process....so when it's accomplished the areas binding the two rods will be far more consistent in strength than any weld could ever be.

I have functional prototypes now. They weigh 27 grams for a complete 17" rod. The catalog company rods are between 120 -130 gms. The prototype molds will be made over one more time....then the margins will be good.

The materials are certified for aviation (Hexcel makes this stuff). Aviation uses composites because the various molding processes used to fabricate these materials are so refined at this point that the molded parts are utterly consistent. The simple loads of a truss rod are a PERFECT application of uni-directional carbon fiber...and a refined compression molding process will yield a rod with a strength margin almost exactly the same for each rod.

What this means to builders is that they will get a product that is 1/5th the weight of a typical rod....and that they'll know exactly how many turns from nominal it WILL take to break it....and that it will bend their neck like a banana before it breaks...and that the next one will be exactly the same as the last one.

_________________
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

Now that's got my attention! What sort of price point are you aiming for? Probably too expensive for me except on special occasions (like harp guitars, which really need light weight in the neck direction), but still sounds like an excellent option to have available.

Lol....weight is the deal with carbon fiber. The tensile strength of properly processed carbon fiber is almost ten times that of 1018 steel....which is one of the likely common steels some of these other rods are made from. Machinable, weldable, inexpensive steels are in this same range of strength.

Did you know the new Airbus A380 is 53% composite...and the Boeing 787 is 50%? We are flying around in plastic now folks. i'm pretty sure truss rods can stand a little more tech.

It takes 56 minutes to make one...plus materials. I've timed every operation accurately. Hoping to keep it near $50 wholesale. Truss rods are price sensitive...I know...but they are 1/5th the weight and if the strength pans out like I think it will...it'll be fairly priced for what it is.

_________________
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

Btw....whatever changes I make from here on out...aren't going to change the weight....just make them stronger.

_________________
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

Stuart, That makes perfect sense and it sounds like fun project to boot.
I like the fact that your using prepreg and I have a soft spot in my heart for Hexcel.

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Jim Watts
http://jameswattsguitars.com

Hey Stuart! The weight reduction alone would be huge to me personally. The Blanchard rods that I mostly used were around 119 grams IIRC and losing 90 grams would be a huge plus to how I build.

I'd be interested in the dimensions of the required channel. One of the issues that we've seen with the SM HotRod is the additional depth required for the channel. We've see at least three of them split out the back of the neck because the maker went too thin with a thicker rod.

CF also is likely to be more buzz resistant and that would be a plus too.

The Blanchard rod being stainless thankfully deals with another truss rod issue. Over time some rods, not the Blanchard rod, can corrode making them not work well. It's standard fare on older G*bsons to remove the nut completely, lube it up, and put it back on in an effort to deal with the corrosion over time. Be nice not to have to do that.

Welcome back!

I had too may fail that had a weld on the threaded rod. Give me the Martin style or the compression gibson style 1 way rod. Personally I think a 2 way rod is overkill.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

It sounds awesome Stuart! I'm very excited to see it when you are done-

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Burton
http://www.legeytinstruments.com
Brookline, MA.

The Hot Rod is a very good design from the standpoint of breaking....but sadly....it can't be made shallower without sacrificing a huge strength margin. I can't use them either because of the height. This design is .25" x .35". The thing about molding them though is that they mold very precisely from part to part....so the tolerances will be very tight. I expect to publish a tolerance of + or - .002" for those dimension. I shouldn't be so bold but that's what the 40 or so rods I've produce so far have measured.




Molding allows for specific geometry features. I'd love to say more on this but the provisional patents have not yet been awarded. I can safely promise though....these rods have several provisions that address this issue of buzzing DIRECTLY.



Yes...and direct contact of carbon fiber to certain alloys, with an electrolyte (water vapor) present, will promote galvanic corrosion. Graphite is about as much of a cathode that one can find on earth....and Grade 8 steel is about halfway up (or down ) the list from cathode to anode...so it's definitely something I've considered when designing this....but it is addressed with this design by eliminating the prescience of an electrolyte...and this won't change over time...I hope. I had a friend that had an aging and weatherization testing lab....but this isn't his typical scenario...he tests storm windows for that most part. I might do something test-wise...might not..and just rely on the fact that there is no electrolyte present.

_________________
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

Yes John...I remember you mentioning the Martin rod as a fairly fail proof design. I'll be comparing mine directly against that one...as well as a few others.

_________________
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