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Trussrod Replacement


stewblack

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56 minutes ago, 3below said:

The unmentionable bass (looks very similar to yours) that I owned many years ago also had an incredibly thick fingerboard with the same style binding.  In this respect the Shaftesbury is being faithful.

Really good work so far and so rewarding when a DIY job saves the day.  Having recently encountered (for the first time ever) a neck with a back bow I would use a double action rod if you can.  If you need a strip of maple to fill the truss rod channel bed for the double action rod put the dimensions up on here.   

I think you may have meant this for the OP.

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3 minutes ago, stewblack said:

I'm happier scraping a bottom than trying to stuff something in it.

I am lost for words :).  Does this mean that you need to deepen the channel, no infill needed?  I was just warming the planer-thicknesser and bandsaw up :)

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51 minutes ago, stewblack said:

I'm happier scraping a bottom than trying to stuff something in it.

I would want to know how much wood there is between the bottom of the truss rod channel and the back of the neck before even contemplating this.

And find out from those who build guitars what the minimum thickness they would be happy with is. @Andyjr1515

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I'm just wondering if there would be an issue using a double acting rod as it is designed to bend to oppose the force of the strings - it would potentially put pressure on the back of the neck at the nut and heel and possibly split the wood if it is that thin. A single acting rod would be applying compression down the length of the neck to prevent it bending as far as I can tell.

Again, not something I've tried, just a thought! 

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38 minutes ago, Jabba_the_gut said:

I'm just wondering if there would be an issue using a double acting rod as it is designed to bend to oppose the force of the strings - it would potentially put pressure on the back of the neck at the nut and heel and possibly split the wood if it is that thin. A single acting rod would be applying compression down the length of the neck to prevent it bending as far as I can tell.

Again, not something I've tried, just a thought! 

Good point

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I imagine it is now possible to determine how much wood is left under the truss rod channel, by measuring the depth of the channel at the deepest point, somewhere towards the middle of the neck (with the rod removed). Measure the overall thickness of the neck (minus the fingerboard now) and subtract one measurement from the other.

That should help to tell how how risky the adoption of a double action rod would be. Personally, I guess you haven't got enough depth for a double action rod.

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10 minutes ago, songofthewind said:

depth of the channel at the deepest point, somewhere towards the middle of the neck

Hi SOTW, did this and it actually gets shallower just towards the heel!

Edited by stewblack
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A traditional single acting trussrod sits in a curved slot:

eHKr93eh.jpg

So - assuming that the top face of the neck is flat then, as @songofthewind says, the slot should vary in depth, with the deepest in the middle.  If it doesn't - or if it does but only by a tiny amount - then this might be why the rod broke in the first place.

If it does, then you could fit a single action rod in the slot, and then you will need to carve a curved packer (to replace the one you had to remove to get the rod out) shaped like in the photo above.

A single acting trussrod is fitted curved in a curved chamber like in the photo.  They will only work if the channel and packer are curved the right amount

But if the slot is at least 9mm deep at either end, then that is deep enough to fit a double acting trussrod.  These are fitted straight and they will bend whether or not they are in a channel:

Untensioned:

rAaRGQtl.jpg

Tensioned:

QHejof0l.jpg

So, if the channel is deep enough at both ends, one of these would fit.  And it's a lot easier than worrying about the amount of curve in the channel and creating that curve.

So then the remaining question is the one that @Jabba_the_gut raises.

That is:

Because we know your fretboard is very thick, it implies that the neck itself is quite thin.  So how thick is the neck at around the first fret (or closer to the nut if it is clear of any volute)?  If it is at or more than 13-14mm, then you have a channel at 9.5mm and that would leave you 3.5 -4.5 mm wood below the slot - which would be plenty.  If, say, the neck at the 1st fret is 12mm, then that only leaves 2.5mm of wood under the slot and, when a 2-way truss rod end starts applying the pressure, it is possible that it might crack the bottom of the neck under the nut.

So if it is thick enough, a 2-way rod would be much easier to fit.  If it's worryingly thin, then a single action replacement would be safer, albeit a little trickier to fit properly.

:) 

 

 

Edited by Andyjr1515
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I'm staying in the shed. Right, taking volute to mean the bit that starts to curve towards the headstock, I measured as close to the nut as I could where the neck was still straight. 

It's 13.5mm there but drops to 12.5mm thereafter. Until the 7th fret(ish) where it deepens to 14mm, rising to 15mm as we approach the heel. Oh and its 5mm wide

Not quite the perfect angle but you can see within a mm how shallow it is. IMG_20200515_184003.thumb.jpg.15f9a86388eb5443ffe14e3226302a1d.jpg

Edited by stewblack
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This looks like it will be a close decision between two way or single rod.  Some  more measurements will help. I would suggest starting at the nut and repeating the measurements of neck depth every cm down the neck until you get to the 7th fret. This would aid accurately determining the overall profile and whether a two way rod could go in further into the neck (longitudinally not depth) aiming  to get the pressure point away from the 'too thin' timber.   If you then install the rod with the flat upwards you also have some latitude to strengthen the 'thin' wood under the adjusre nut with epoxy / epoxy + carbon fibre.

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Well all this may be academic. As I was putting the bass in its case I felt a sharp edge catch my skin. Turned it over and the neck has started to split. 

All good narratives need our hero facing certain defeat, but is there a redemptive ending to this story? 

IMG_20200515_185219.thumb.jpg.3b6d20e296eb76cc3330fa490eead6c1.jpg

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Goodness!  Wasn't expecting that!  In fact, like @Maude can't think what could have caused that at all!?

Does it look like it's the wood or could it be just the lacquer?  If it's the lacquer, you have a bit of extra finishing work to do, but the options on the neck remain as they were.

Assuming I'm right - those measurements tell me you need to be sticking with a single action.  There might be just 2mm under there - and that's not enough, really 

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