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Truss rod choice for OM build

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Truss rod choice for OM build

Postby Bob Howell » Mon Jul 25, 2016 9:26 am

I am gathering materials for the OM feachered in Alex Willis book.

The truss rod described at SM is just a 3/16 steel rod(plain or all thread) with a barrel nut which you can get at most hardware stores.

Is this all I need? The Hotrod is more complex but do I need it? Just $16.

This is my first guitar build and I'm using Maple/walnut/cherry woods I have re-sawed in my shop; even the sound board is from wood I got from Aircraft Spruce.

So this is a learning experience.

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Re: Truss rod choice for OM build

Postby Brian Evans » Mon Jul 25, 2016 10:00 am

The single action, or Gibson style, truss rod is in a whole heck of a lot of guitars and does a decent job. It is trickier than 3/16" all thread and a barrel nut, although that's indeed what it looks like. The barrel is drilled and welded so that it cannot come loose, the channel is routed or sawn with a curved path so that it's deeper in the middle and the body end than at the headstock end, and you need to have a metal stop imbedded in the neck at the headstock end. So it looks simpler, but is more complicated to make and install than the Hotrod type. The Hotrod type is designed so that it has dual action, can bend the neck forward or back, it is installed in a very simple straight channel in the neck, and you can arrange it so that you can access the adjusting nut from inside the body of the guitar, so the headstock end is simpler and stronger. I've done the Gibson style mostly so I could say I've made one, and I'm switching to the Hotrod type. Better, simpler, and if I count my time as worth minimum wage, cheaper...
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Re: Truss rod choice for OM build

Postby Bob Howell » Mon Jul 25, 2016 11:45 am

Thanks, Glad for the explanation.

Hotrod it is.
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Re: Truss rod choice for OM build

Postby Rodger Knox » Mon Jul 25, 2016 12:14 pm

You might want to use something like this:
http://www.stewmac.com/Materials_and_Su ... s_Rod.html
or this:
http://alliedlutherie.com/collections/f ... 6364138310
The hotrod requires a pretty deep channel, which limits how thin you can make the neck.
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Re: Truss rod choice for OM build

Postby Alan Carruth » Mon Jul 25, 2016 12:44 pm

I've been getting truss rods from Mark Blanchard. He came up with an improvement on the usual double action rod, which has 10-32 left hand thread on one end, and 10-32 right hand thread on the other. Each turn of the rod makes it 1/16" longer or shorter, and that can take a lot of force. Mark uses right handed thread on both ends, but with different thread counts; 24 per inch at one end and 32 at the other. This changes the length by the difference (which, if I remember correctly, is 1/96 inch) per turn. Essentially, it's like having 3:1 gearing; you take three times as many turns, but with 1/3 the force.

Originally he licensed the design to Allied, and they got them made in China. The early batches were not so well made: I had some problems with the rod buzzing, and other folks had failures in the brazed joint between the rod and the nut at the end, I'm told. Mark started making his own, and the latest ones I've gotten have the rod nicely machined out of stainless steel, eliminating the brazing at the ends. I gather that Allied has also changed their supplier, so those may be working better too.

There's no getting around the fact that Mark's rods are more expensive then many. They also work better, IMO, and are very well made. That latter may not mean much to some folks, but I like the notion of working with a craftsman who takes as much pride in those unseen details as in the rest of the guitar. Besides, Mark's a hecuva nice guy...
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Re: Truss rod choice for OM build

Postby Todd Stock » Mon Jul 25, 2016 3:34 pm

I recommend against using the Spanish heel design in Willis' book for a steel string. As a repairman and as someone that teaches steel string construction, Spanish heels on steel stringed guitars does not reflect general industry practice, complicate getting the correct neck angle set, and make finishing more difficult - particularly for a new builder. Either Cumpiano (with suitable updates) or Kinkead are better guides, with Kinkead showing modern construction techniques like go-bar deck and outside mold construction, and Cumpiano doing the best job on explaining tasks like binding and trimming purflings. Cumpiano bolt-on neck mixed with radius dish/outside mold/go-bars is a popular approach and is pretty well covered here and on other sites.

I would suggest using the Martin rod - inexpensive, easy to install, shallower than several other rods, and does not require mods to the UTG to fit properly. A 1/4" hole set 1/16" up from the glued edge of the UTB and centered handles access for adjustment.
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Re: Truss rod choice for OM build

Postby David King » Mon Jul 25, 2016 7:04 pm

I'd concur with Todd that the "Martin rod" is an excellent choice for a first guitar (although Martin hasn't used it themselves in years.) I liked all of the rods I got from LMII for my testing. I'd also say that the Hot Rod is by far the deepest installation that requires a very thick neck to contain it. In the long run, a single curved rod is probably your best bet but it takes considerable tooling to deal with it efficiently.
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Re: Truss rod choice for OM build

Postby Alan Carruth » Tue Jul 26, 2016 1:00 pm

Back when I started out I made steel strings, including 12s, with Classical type heels. They work, but....

The real problem is not with the neck angle per se; you can get that right initially, and the neck doesn't generally move. The issue is that the box deforms under the constant string load. This is less of a problem with Classical guitars, with the lower string tension, but even they have issues over the long run. The traditional approach was, as far as I can tell, to use a really thick fingerboard, so that when the action does get too high you can pull the upper frets and plane it down a bit. You don't usually get tot do this more than once on a particular guitar, of course. Another approach is to plane the the fingerboard down and laminate another piece on top.

Being able to remove the neck is a real improvement. Although the dovetail joint is traditional in American guitars, and practically a religion in some circles, there are other ways that work well. Again, I've tried most of them. Recently I've been using a bolt-on neck, and it's fine.
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Re: Truss rod choice for OM build

Postby Todd Stock » Tue Jul 26, 2016 2:32 pm

David:

The old single action Gotoh style Martin rod used from the mid-1980's through 2005 is an excellent truss rod, and as you suggested, is no longer in use on any Martin guitars; however the Martin rod I am suggesting is the newer (post-2005) double action truss rod in service on something like 750,000 instruments. By way of recognizing these, they are completely covered with a shrink-wrap plastic, while the knock-offs have covering only on the operating end.

To my knowledge, only Martin is selling that rod at $13 per through Guitar Maker's Connection (Blues Creek Guitars and other vendors like StewMac are selling a similar rod, but it is not the Martin rod). Rods are available in 12 and 14 fret lengths, as well as one that will work for a Size 5 - the Size 5 rod is not on the web site, but can be purchased with a call to GMC. Either buy the short/long truss rod wrench on the site or mod a 5mm ball end T-wrench.

https://www.martinguitar.com/1833-shop/14-fret-two-way-truss-rod/c-24/p-486

https://www.martinguitar.com/1833-shop/12-fret-two-way-truss-rod/c-24/p-487

https://www.martinguitar.com/1833-shop/truss-rod-wrench/c-24/p-476

On getting the neck angle right initially - I see one or two builders a year that get this wrong and then ask me to correct the issue. With Cumpiano bolt-ons or Kinkead/StewMac dovetails, it's usually a quickly fixable thing, but on the Sloane and Willis guitars that have come through, it's generally a 'cut neck off/convert to bolt-on' job that costs the builders some time to refinish, etc. I agree with Allan that first time builders can get this right, but it is painful when a percentage of folks don't.
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Re: Truss rod choice for OM build

Postby Alan Carruth » Wed Jul 27, 2016 12:09 pm

The 'Spanish heel' is, of course, part of a system of building that involves the use of a 'solera' to establish the neck angle and alignment as the build proceeds. It has been argued that this system came about as the older guild system failed in Spain. Lesser trained makers didn't have the tool chops to produce plug-in (or, as was often the case, nail-on) necks with any facility. They came up with a fixture that got around the problem and sped things up. The down side was that the neck was not easily removable. It's not difficult to make a guitar with a removable neck on a solera, but you do need to be able to make the joint.
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Re: Truss rod choice for OM build

Postby Bob Howell » Tue Aug 09, 2016 6:09 am

Finally located my copy of Cumpiano's book and am studying/understanding my options.

Is there an update somewhere. In his interview he mentions the difficulty as if he had done one.
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Re: Truss rod choice for OM build

Postby Bryan Bear » Tue Aug 09, 2016 10:20 am

he has a website that lists several updates to his book. Some are minor clarifications but there is a major update to his neck joint there.
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Re: Truss rod choice for OM build

Postby Peter Wilcox » Tue Aug 09, 2016 10:35 am

Maybe I can't fix it, but I can fix it so no one can fix it
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Re: Truss rod choice for OM build

Postby Bob Howell » Sun Sep 18, 2016 8:38 pm

I got the double action on sale at LMI and am now working on the neck. There are a lot of options for rods, with little apparent difference.

Read somewhere to colored markers and mark up the GTT book to separate the SS and classical build. That solves a big problem I'm having so on to that.
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Re: Truss rod choice for OM build

Postby Bob Howell » Thu Aug 17, 2017 1:35 pm

Todd Stock wrote:David:

The old single action Gotoh style Martin rod used from the mid-1980's through 2005 is an excellent truss rod, and as you suggested, is no longer in use on any Martin guitars; however the Martin rod I am suggesting is the newer (post-2005) double action truss rod in service on something like 750,000 instruments. By way of recognizing these, they are completely covered with a shrink-wrap plastic, while the knock-offs have covering only on the operating end.

To my knowledge, only Martin is selling that rod at $13 per through Guitar Maker's Connection (Blues Creek Guitars and other vendors like StewMac are selling a similar rod, but it is not the Martin rod). Rods are available in 12 and 14 fret lengths, as well as one that will work for a Size 5 - the Size 5 rod is not on the web site, but can be purchased with a call to GMC. Either buy the short/long truss rod wrench on the site or mod a 5mm ball end T-wrench.

https://www.martinguitar.com/1833-shop/14-fret-two-way-truss-rod/c-24/p-486

https://www.martinguitar.com/1833-shop/12-fret-two-way-truss-rod/c-24/p-487

https://www.martinguitar.com/1833-shop/truss-rod-wrench/c-24/p-476

On getting the neck angle right initially - I see one or two builders a year that get this wrong and then ask me to correct the issue. With Cumpiano bolt-ons or Kinkead/StewMac dovetails, it's usually a quickly fixable thing, but on the Sloane and Willis guitars that have come through, it's generally a 'cut neck off/convert to bolt-on' job that costs the builders some time to refinish, etc. I agree with Allan that first time builders can get this right, but it is painful when a percentage of folks don't.

I have need more truss rods and based on this I'm looking at Martins. Its seems simple and I'm wondering just what the difference is between them.

Also , Cumpaino recommends first time builders make the access through the sound hole. Seems to me the head plate makes more sense. Why the caution. What are the trade offs.

I used the bolt on neck
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Re: Truss rod choice for OM build

Postby Barry Daniels » Thu Aug 17, 2017 9:10 pm

I make gibson style single action rods from 3/16" carbon steel rod. I bend a right angle hook on the heel end and thread the upper portion for a brass acorn nut or fender style bullet nut (if I want to leave it exposed). Heat shrink gets applied to the rod to prevent rattles. To give some dual action adjustability, I place a bit of tension on the rod before I level the fretboard. The rod gets installed in a slot that curves upward towards the headstock. This rod is the lightest there is and it has little that can go wrong. The materials also cost only a buck or two.
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Re: Truss rod choice for OM build

Postby Alan Carruth » Fri Aug 18, 2017 12:55 pm

The main problem IMO with accessing the truss rod nut at the head end is that you need to cut a channel in the headstock for it. This further reduces the strength of the neck in a place that's already weak. I've seen lots of head breaks over the years in that spot, just above the nut before the head flares out. The neck at the nut is narrower by a little bit, but has the fingerboard glued on which adds stiffness and strength. Also, if you're using the common one-piece neck and head that area has short grain.

You can gain a fair amount of strength by putting on a back strap: a veneer on the back surface of the head that runs up onto the neck. It's bent to make the corner, so you replace the sort grain with wood that's running along the surface. I've actually made guitars with no face veneer on the head, but only a back strap.
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Re: Truss rod choice for OM build

Postby David King » Fri Aug 18, 2017 2:43 pm

On single compression curved rods I thread both ends and thread on a flat 5/8" x 1/4" thick aluminum disc anchor. I then peen the threads at the anchor so that the rod can't come unscrewed. The rod need at least 3/16" of drop in the middle to work well, I'll do more if I have the room in the neck. I'll drill the hole for the anchor with a Forstner bit at the same angle as the rod, usually between the nut and the first fret. I coat the rod with carnuba or Johnson's paste wax before installing it and glue a spline of hardwood into the slot, on top of the rod, clamping it down firmly enough to prevent it from rattling. I'll test the rod while the glue is drying to make sure that the rod is free to move in the slot. Pounding on the back of the neck assures me that the rod isn't rattling. The end grain where the adjusting nut will be putting pressure can be hardened with thin CA to help prevent it from collapsing over time.

Rod material is important. A low carbon hot rolled steel (HRS) only has a PSI strength of 36000 while cold rolled steel is around 58000, annealed O1 drill rod hits 109000 PSI and music wire can reach 230000 PSI. I wouldn't recommend the music wire as it's nearly impossible to thread but O1 is great and threads easily. You DON'T want to harden it as that will just make it brittle without adding much to the strength.
Some places sell stainless steel rods which are also fine but somewhat harder to thread.
Threads make a difference as well, rolled threads are stronger than cut threads but require a thread rolling mill which isn't practical for the home shop. Rolled threads also start with a smaller diameter rod since no material is removed in the process. A rod is only as strong as it's weakest point so a 3/16" rod, threaded 10-32 is only as strong as the minor thread diameter which is .151".
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Re: Truss rod choice for OM build

Postby Todd Stock » Wed Sep 06, 2017 7:36 am

Neck access is generally something that requires two tools (tool to remove cover plate and truss rod wrench) and as Alan mentioned, weakens the head stock quite a bit. Ask any guitar repair person for the makeup of the broken necks they see, and the overwhelming majority will be Gibson or Gibson clones. If the access is very carefully done, with minimal material cut away and good grain orientation trough the neck-to-peghead tension - which is closer to the Taylor model - the design works well in service, and with a single action rod, is lighter than other adjustable truss rod designs.

Soundhole truss rod access is a single tool event, although manufacturers like SCGC and Larrivee and a few custom builders make this more exciting than it needs to be by requiring pretzel wrenches to get around the UTB. A 1/4"/6.35mm hole through the UTB on centerline which leaves a 1/16" or more of material between the edge of the hole and soundboard glue joint is more than enough to carry compressive and tensile loads and will still take a 5mm wrench for adjustment. Martin and other manufacturers oversize that hole, but with just a minimum of care in alignment of the neck (which is needed more to ensure the strings remain over - not beside - the fretboard extension), a 1/16" oversized is more than enough. for clearance.


There are a number of threads on various truss rods available and their pros and cons. As a repair guy that builds, I've seen enough failed and failing truss rods to know what risks I'm willing to take and which rods I would definitely NOT build with, but that leaves close to a dozen vendors to choose from, and at least 4 distinct designs (one-way tension, one-way aluminum channel tension, two-way aluminum tension, two way two rod). My own decision-making process places more emphasis on reliability, effectiveness, and ease of installation than lightest weight or lowest cost, so I use the most reliable rod I can find and minimize weight by using lighter tuners and careful selection of neck stock. Your priorities may and likely should vary, so do your research and pick a winner.

The Hot Rod is on my list of 'never again's...requires too deep a channel, is heavy, and - from what I have seen in terms of other builders and repairs - not reliable enough in use to warrant risking a truss rod swap further down the road.
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Re: Truss rod choice for OM build

Postby Barry Daniels » Wed Sep 06, 2017 10:47 am

Well said, Todd.
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