How to lock a nut tight on a threaded rod ?

[murrmacParticipant @murrmac]

I am in the process of building my next guitar, and am proposing to install an unorthodox style of neck truss rod.

This rod, roughly 18" long, will consist of a 5mm round bright steel rod with a right hand M5 thread at one end and a left hand M5 thread at the other. both threads will go into tapped plates inserted at either end of the neck.

The idea is that turning the rod clockwise will compress the neck and turning anti clockwise will decompress it.

At the adjusting end, I propose to fit a M5 connector nut, which needs to be firmly affixed to the threaded end of the rod to resist the torque.

I am thinking that it might be possible to do this by hard soldering ? Or to be specific, that someone else might be able to do it by hard soldering … I would be perfectly willing to pay if anybody on the forum here has the facilities and the ability to do this .. I certainly don't have the chops for it… wouldn't even know how to start.

After the nut is soldered, (assuming that is feasible) then I would further reinforce it by drilling the nut and inserting a couple of 2mm silver steel "cross rods" (there must be a proper name for them)

If hard soldering isn't a good idea, then what would be the best way to go about locking the nut ? Maybe the most tenacious grade of Loctite, followed by the mechanical reinforcement?

As always, TIA for any advice.

[murrmacParticipant @murrmac]

[Jon GibbsParticipant @jongibbs59756]

I'd use Loctite stud-grade. Much less effort and less messy than trying to solder/braze.

If you're using M5 rod and a long connector nut, I'd expect that the rod will break before the Loctite bond if you de-grease and clean the threads thoroughly.

HTH

Jon

[Ian PParticipant @ianp]

I think Jon's method will be more than adequate. Your left and right threaded arrangement is very common in 'Bottle screws' for boat and aircraft cables. The double threaded component is often quite short though and is turned near its midpoint with flats or its heaxagon shape.

I assume that you are intending to adjust the rod tension by just rotating the attached nut (which is only at one end?)

One problem you will probably find is that the thread at the far end will only move in fits and starts. The friction of the threaded rod in the fixed nut will be quite high when its under tension so the rod will 'wind up' like a torsion spring.

Ian P

[NobbyParticipant @nobby]

HI
Add another M5 nut and lock the two together on the rod
Nobby

Edited By Nobby on 19/09/2014 11:57:48

[murrmacParticipant @murrmac]

Thanks for replies so far … silver soldering out of the question, then… Loctite stud grade it is.

The two double locked nuts sounds feasible, but I feel it would still require Loctite (and cross-pins) … still, belt and braces and all that …

I get Ian's point about the torsion spring effect. I am hoping that using 5mm rod will minimise the torsion (I would actually have preferred 4mm for lightness) , but I feel that 4mm definitely would have torsion problems.

The tapped plate at the far end will be made out of brass, and will be lubricated prior to the neck being glued up, so I am hoping that it will move freely.

I mistakenly said the rod was 18" long … it is actually more like 14" .

[Jon GibbsParticipant @jongibbs59756]

I think Ian's comment about the torsion delay over even 14" may be quite serious though. It's quite likely to result in the rod twisting in two at a weak point eventually if there's any real tension in the arrangement.

While the double thread is elegant in one way and ought to be twice as fast, is speed in adjustment really necessary?

Why not fix one end of the rod and use the connector nut as the means to tighten/slacken the whole arrangement and/or change the thread pitch from 0.7 to 1 or 1.2mm to ge tthe speed back?

HTH

Jon

[murrmacParticipant @murrmac]

Posted by Jon Gibbs on 19/09/2014 12:25:10:

While the double thread is elegant in one way and ought to be twice as fast, is speed in adjustment really necessary?

Why not fix one end of the rod and use the connector nut as the means to tighten/slacken the whole arrangement and/or change the thread pitch from 0.7 to 1 or 1.2mm to get the speed back?

HTH

Jon

Ah well … you are right into the heart of the matter, Jon, and this is one of the more abstruse and much debated topics among guitar makers. Firstly, it's not about speed … it's unlikely that the rod would ever require more than a couple of full turns at any time in its life … absolute max, and more like a quarter of a turn..

What you are describing with the anchored end is in fact a common way of implementing truss rod installation, and is known in the biz as a single action compression rod. This type of rod is good for adjusting a concave bow in the neck/fingerboard, but cannot adjust a convex bow . What I am proposing is a "dual action " rod, which will be able to correct both convex and concave bows. There are of course dual action truss rods commercially available, but they all suffer from a few disadvantages, discussion of which is probably irrelevant in this thread.

The rod I am proposing is much more time consuming to fabricate and install, but would , I believe, result in a superior product.

[Jon GibbsParticipant @jongibbs59756]

Thanks for the explanation.

Apologies for the naiive questions/comments.

Jon

[Neil WyattModerator @neilwyatt]

5mm sounds a bit light to me. Even a 4mm truss rod would happily take the tension, but I would be seriously worried about stripping the thread on the moving nut. You also will need quite a lot of room to access an M5 nut.

All my guitars have a 5mm internal hex for an allen key on the truss rod which suggests that they are M6.

I'm not sure if it's the 'official' technique but I find that any torsion delay when adjusting the truss rod is easily overcome by delicately rapping the back of the neck with the heel of my left palm. You hear a couple of clicks and things settle down. Don't do this and the neck will not stay where it's put.

Funnily enough, moved my acoustic to a new room for its home recently, and it got a couple of buzzes on the low E string – I had to back off the truss rod about 1/2 turn. It really deserves a re-fret as it's over 40 years old (and I thought it was old when I bought in 1983! – Got my parents to fund it as my 21st birthday present.)

Neil

[Anonymous]

Posted by murrmac on 19/09/2014 12:43:30:

What you are describing with the anchored end is in fact a common way of implementing truss rod installation, and is known in the biz as a single action compression rod. This type of rod is good for adjusting a concave bow in the neck/fingerboard, but cannot adjust a convex bow . What I am proposing is a "dual action " rod, which will be able to correct both convex and concave bows.

Does that imply the rod can be in tension, or compression, depending upon the bow to be corrected?

Regards,

Andrew

[murrmacParticipant @murrmac]

Neil, your 5mm hex nuts, believe it or not, go onto a M5 thread . You can easily test this by removing the nuts completely and trying them on a known M5 thread. If you can remove the nuts, then your truss rod is single action. If you cannot remove the nut, ie if it is immovably fixed to the end of the rod, then it may well be a dual action rod… you will probably know yourself which type you have.

Your truss rods are, I suspect, single action rods, but they are not "compression" rods. Your rod acts by compressing a bar which sits above the round rod, and which forces the cente of the fingerboard up when it is tightened. This is subtly different in operation from the "compression" style rod (which Gibson used for many years, maybe still do)

You can get dual action rods (and yours may well be dual action ..I don't know for sure) which have a bar across the top of the rod,( which has a left and right hand thread) but the problem with these is that there is a neutral point at which the rod does nothing, but just sits there … personally, I believe the neck is better served by being under compression below the neutral axis, compression which is countered by the tensile pull of the strings.

At the end of the day, what I am proposing may not work satisfactorily and I will return to the single action rod which Jon outlined above, anchored at one end and adjusted with a nut at the other … no rod torsion to worry about.

5mm is IMO a maximum for any truss rod, both from the point of view of added weight, and also to keep invasive routing and excess wood removal from the neck to a minimum.

Your technique for adjusting the neck is spot on btw …I personally put instruments into a jig which forces the neck up slightly before I tighten the truss rod … same principle.

[murrmacParticipant @murrmac]

Posted by Andrew Johnston on 19/09/2014 14:00:10:

Posted by murrmac on 19/09/2014 12:43:30:

What you are describing with the anchored end is in fact a common way of implementing truss rod installation, and is known in the biz as a single action compression rod. This type of rod is good for adjusting a concave bow in the neck/fingerboard, but cannot adjust a convex bow . What I am proposing is a "dual action " rod, which will be able to correct both convex and concave bows.

Does that imply the rod can be in tension, or compression, depending upon the bow to be corrected?

Regards,

Andrew

Hi Andrew, yes, that is in fact what it means. On a well made guitar It is unlikely ever to be in compression, but I am preparing for any eventuality. There are other concerns such as the stiffness of the fretboard, which I am reinforcing with carbon fibre inserts… it may be that the pull of the strings is not sufficient to give the required relief, in which case the trussrod would in fact be put into compression. That is not likely however, leastways I hope it isn't..

[Anonymous]

Posted by murrmac on 19/09/2014 14:36:17:

Hi Andrew, yes, that is in fact what it means. On a well made guitar It is unlikely ever to be in compression, but I am preparing for any eventuality.

It might be prudent to prepare for buckling of the rod too. The slenderness ratio of a column is the ratio of length to least radius of gyration. For a solid circular column the least radius of gyration is d/4, or 1.25mm in our case. The length of 14" equates to 355.6mm, so that gives a slenderness ratio of 284. That puts the rod firmly in the camp where buckling will predominate over any compressive stresses. In this case the Euler formula can be used to calculate the load.

I assume that the rod is constrained within some sort of channel? That may help with buckling but will increase the torque needed as the rod pushes against the side of the channel.

Regards,

Andrew

Edited By Andrew Johnston on 19/09/2014 15:18:56

[murrmacParticipant @murrmac]

Yes, the rod is held within a 6mm diameter routed channel in the neck, It is also covered in heatshrink wrap as a precaution against any rattling or buzzing,

The proper way to install a rod like this (and of course the way which I am doing) is to install it when the neck has not yet undergone final shaping, but enough material has been removed from the back to impart a slight convex bow to the neck when the rod is tightened. The bow is then planed flat, and the fingerboard glued on. This means that the truss rod should remain in tension and never be required to be in compression.

The adjustments required in a truss rod are really very slight … half a turn of the nut makes a huge difference to the plane of the fingerboard (but "huge" is still measured in terms of only a few thou)

[Peter G. ShawParticipant @peterg-shaw75338]

One thing does concern me, and to be frank, I don't know enough to know if I should be concerned. I hope others will comment further.

You talk about:

"After the nut is soldered, (assuming that is feasible) then I would further reinforce it by drilling the nut and inserting a couple of 2mm silver steel "cross rods" (there must be a proper name for them) "

Whilst I understand the purpose of the cross rods, I do wonder if you may be weakening the 5mm nuts and bar too much. As I say, I'm no expert, but 2mm does seem to be a substantial portion of 5mm. Going back to my school days, I was taught in woodwork, that a tenon on a mortice and tenon joint should be no more than one third the wood thickness. Applying this principle here would suggest 1.5mm rather than 2mm.

Also, do I understand two cross rods per nut, as this would weaken it even further?

Regards,

Peter G. Shaw

[murrmacParticipant @murrmac]

You are very probably correct, Peter, and I shall revise my spec to 1.5mm silver steel cross dowels.

I think that two isn't excessive in a M5 studding connector nut … they should be far enough apart … just IMO, I could be wrong.

[murrmacParticipant @murrmac]

I just realised that I failed to mention that this is a flat top round hole acoustic guitar, not a solid bodied electric.

Neil's earlier point about needing plenty of access is valid, and it would indeed be problematic if the adjustment were at the headstock, but the adjustment will be done from inside the body of the guitar, at the neck block, so access isn't really a problem.

[Michael GilliganParticipant @michaelgilligan61133]

murrmac,

Please don't bother … just reduce the dowel diameter to zero.

Loctite 638 or similar will retain an M5 nut sufficiently well to shear the studding.

… Try it on an offcut.

MichaelG.

.

Edit : this is obviously a response to your post of 16:01:09

Edited By Michael Gilligan on 19/09/2014 16:14:16

[Peter G. ShawParticipant @peterg-shaw75338]

Murrmac,

I've a sneaky suspicion that I have misunderstood the length of the connector nuts in which case my comment re two cross-bars is wrong. As long as the connector nuts are at least say, 10mm long, and the two cross bars separated by say 5mm, then that would remove that concern. All dimensions approximate, of course. Using 1.5mm bars still stands though.

Regards,

Peter G. Shaw

[murrmacParticipant @murrmac]

Posted by Michael Gilligan on 19/09/2014 16:12:21:

murrmac,

Please don't bother … just reduce the dowel diameter to zero.

Loctite 638 or similar will retain an M5 nut sufficiently well to shear the studding.

… Try it on an offcut.

MichaelG.

.

Edit : this is obviously a response to your post of 16:01:09

Edited By Michael Gilligan on 19/09/2014 16:14:16

Thank you Michael, I shall do just that.

That was going to be my next question …exactly what grade of Loctite should I use.

[Neil WyattModerator @neilwyatt]

Murrmac – you obviously know vastly more about guitars than I do!

Neil, your 5mm hex nuts, believe it or not, go onto a M5 thread . You can easily test this by removing the nuts completely and trying them on a known M5 thread.

I'm happy to take your word for it

Your truss rods are, I suspect, single action rods, but they are not "compression" rods. Your rod acts by compressing a bar which sits above the round rod, and which forces the cente of the fingerboard up when it is tightened. This is subtly different in operation from the "compression" style rod (which Gibson used for many years, maybe still do)

I've always tightened them to decrease the bow in the neck, so I assume (across half a dozen of more gutars and basses over the years) so I assume they all work in tension. My acoustic is a mid-70s Epiphone so it may have some sort of Gibson arrangement, but it still acts in the way I'm familiar with.

You can get dual action rods (and yours may well be dual action ..I don't know for sure) which have a bar across the top of the rod,

I have two adjusted at the fingerhole end, but I very much doubt they have dual action rods.

This is all very interesting to me as I do try and keep a small 'stable' of guitars in good condition. My wife bought my daughter a good entry-level acoustic and it needed a fair bit of attention at the nut to get a good action. I later bought my wife an entry level Fender acoustic – it was interesting that despite it's far-eastern origin it was set up immaculately and even came with a 'test certificate' giving (verifiable) string clearances at (I think) the second and twelfth frets.

Buying this guitar was an eye-opener. A fat zero for customer care to a 'Guitar' shop in Birmingham who assumed we didn't know what a guitar was and tried to convince my wife that anything less than a £450 solid-spruce top guitar was unsuitable for a beginner.

On the other hand 5-stars for customer service to Rattle and Drum in Derby! Asked about solid spruce, the assistant said "well my guitar cost £850 and has got a laminated top". He let her try various guitars and helped her choose one that not only played well and sounded good, but had a relatively small folk body, and happened to cost a good 50% less than I expected to pay(and she loves it). They threw in a gig bag for nowt without being asked after she had chosen it too.

It was really good to find a music shop that had a 'model engineering' attitude to selling, finding out the customers needs and selling them something will keep them enthused, rather than frustrated

Neil

[murrmacParticipant @murrmac]

Yes, you don't have to spend a fortune these days to get a nice playable acoustic guitar. Some of the instruments coming in from the Pacific rim are outstanding for the money, nice finish, nice necks, and some of them even have solid tops. Saying that, even the ones with laminated tops can be made to play excellently … it's all in the set-up, and in the fret work.

I can tell you that I have owned several high end handmade guitars in my time, and I have always been amazed at how poor the set-up and the fretwork was on many of these handmade guitars, although the quality of the joinery and the finish was always amazing (as was the sound, in most cases). It's like the builder has expended all his energy on getting the bits fitting right , and getting the lacquer immaculate, and the final step of getting the frets properly leveled and crowned and the action spot on is just too much trouble. Once they are set up, they are always wonderful to play.

I agree about music shops … they vary widely in their approach to customers. My guitar buying days are now over, however. I have a Circa OM , a Bourgeois OM and a Martin OOO-28 which I am about to put up for sale.and that's it . From here on in I am building my own. Glad to hear your wife and daughter are enjoying their guitars, it is a wonderful instrument and everybody should own and play one IMO.

[Neil WyattModerator @neilwyatt]

Instruments are addictive, I've just figured out there are 17 stringed instruments round here, not all mine, thank goodness. One or two of note (Fender Performer and Japanese Tokai SG). 18 if you count a slightly-out-of-tune piano. My brother's collection (mostly Gibsons) is rather bigger…

Just wish I could do them justice!

Neil

[Keith HaleParticipant @keithhale68713]

Considered soft soldering? lower temperature involved

Use a free flowing alloy eg 60/40 tin lead. For a better colour match use silver tin alloy eg 2207

Keith

[Author]

Posts