Trussrod Replacement

[3below]

All is not lost, it has just become rather more involved   Hopefully it is just the laquer, however if not there are several ways out.  How handy are you with the router?

[stewblack]

2 hours ago, 3below said:

All is not lost, it has just become rather more involved   Hopefully it is just the laquer, however if not there are several ways out.  How handy are you with the router?

No idea! Never as much as held one in my hand. 

Let's hope it's just lacquer cracking. 

@Andyjr1515I thought the channel wasn't deep enough in the centre for single action? 

[Andyjr1515]

1 hour ago, stewblack said:

No idea! Never as much as held one in my hand. 

Let's hope it's just lacquer cracking. 

@Andyjr1515I thought the channel wasn't deep enough in the centre for single action? 

Yes - good point.  Let me sleep on it - there's something that doesn't quite add up at the moment in the way I'm interpreting the measurements.   I may need to sketch out how I am seeing the various thicknesses in the various positions and check if I'm right.  At the moment, I can't see how the truss rod was working properly in the first place (which, of course, it might not have been )

[Andyjr1515]

Actually, just sussed it how a single action can work OK with these dimensions and why, even if the centre strip has split, why that might not be a problem.  I'll draw it up in the morning and see if the wise sages around here agree

Edited May 15, 2020 by Andyjr1515

[Andyjr1515]

Microsoft Office update has screwed up Powerpoint, email, etc,etc so I'll have to draw it by hand.  Give me 1/2hr

[BigRedX]

Out of interest how thick is the fingerboard?

[Maude]

Just thinking out loud here, a single action rod must push against the centre of the fretboard and the volute and heel ends of the neck to counter the tension of the strings. This would mean that the cracking in the centre of the neck wouldn't have any direct stress placed on it, making it just a cosmetic issue, to a degree. 

Wouldn't it? 

 

[Andyjr1515]

Right.  I hope you can see this - pesky Microsoft!

'Modern' trussrod (at the top)  Starts off straight and when tensioned bows down at either end and up in the middle.  Because the heel end is rigid, the force is transmitted to the nut end trying to bend it down (which counteracts the string tension which is trying to bend it up.

So the main forces are suffered upwards at the centre of the fretboard and downwards at the nut.

There is a critical thickness needed of wood under the nut end of the rod so that the end doesn't burst through the bottom.  Here, a volute is your friend

Traditional Trussrod (at the bottom)  Starts off bent - pressed down by the shaped packer shown hatched in the drawing.  Because the heel end is held rigidly, as you tighten the nut, the rod tries to straighten.  This produces an upward force on the packer in the middle of the fretboard and a downward force at the nut end of the rod.

There is a critical thickness of wood needed under the nut end just like with the modern rod.  However, in most cases - because the circular rod goes through a drilled hole, you have a greater wood thickness

So - and this was the bit that confused me because many makers curve the bottom of the slot - actually, other than at the nut end, the strip underneath the rod takes none of the forces ( see @Maude 's comment above reaching the same conclusion).  So my view is that, as long as the nut end has enough thickness, your cracking - even if it is in the wood itself - is not structurally important

So, @stewblack - a couple of questions.

1.  In this shot:

 

 ...the rod appears to be sitting is a slot rather than a hole drilled through.  Was this how it was, or has any material underneath the rod end immediately behind where the nut and washer used to be been removed?

2.  See where the broken end of the rod is in this pic.  Are you able to work out relatively accurately how thick the wood is here, including any thickening due to meeting the headstock?

 

My suggestions, to be thrown to my knowledgeable peers are:

a) If this area was never thicker, then the original rod was placing as much force on this spot as a modern trussrod would, providing the main body of the rod reaches at least this point.

b) Other than in this specific area, any cracking of the back strip is structurally insignificant

What do folks think?

Edited May 16, 2020 by Andyjr1515

[3below]

Another possibility entered my consciousness last night.  Infill the truss rod channel with suitable wood glued into it to give a level bed depth of say 6.5 mm.  This should stabilise the crack (if it is one) and give sufficient wood depth behind a dual action rod.  With the fingerboard being so deep it should be possible to router (or chisel or router plane / plough plane) a 3 mm groove in the board so that the flat surface of the rod sits in the board.  Stop the groove at a suitable length so that the the rod emerges from a flat (non grooved) end of the board at the nut end.  By doing this the truss rod cover will sit against the fingerboard as before and no sign of the channel in the board will be visible.    The 6.5 mm / 3 mm dimensions are obviously subject to the actual truss rod, board and neck depths available.  I am sure there are flaws in this plan that will be picked up by others

[Andyjr1515]

27 minutes ago, Maude said:

Just thinking out loud here, a single action rod must push against the centre of the fretboard and the volute and heel ends of the neck to counter the tension of the strings. This would mean that the cracking in the centre of the neck wouldn't have any direct stress placed on it, making it just a cosmetic issue, to a degree. 

Wouldn't it? 

 

Yes - absolutely.  See above

[Andyjr1515]

6 minutes ago, 3below said:

Another possibility entered my consciousness last night.  Infill the truss rod channel with suitable wood glued into it to give a level bed depth of say 6.5 mm.  This should stabilise the crack (if it is one) and give sufficient wood depth behind a dual action rod.  With the fingerboard being so deep it should be possible to router (or chisel or router plane / plough plane) a 3 mm groove in the board so that the flat surface of the rod sits in the board.  Stop the groove at a suitable length so that the the rod emerges from a flat (non grooved) end of the board at the nut end.  By doing this the truss rod cover will sit against the fingerboard as before and no sign of the channel in the board will be visible.    The 6.5 mm / 3 mm dimensions are obviously subject to the actual truss rod, board and neck depths available.  I am sure there are flaws in this plan that will be picked up by others

Yes - a valid solution. 

But a tricky rout even with experience and an absolute no-no for someone with no experience.  It's possible, though (see above) it doesn't actually need those extra steps.  We'll see what the other clever folks think

[3below]

4 minutes ago, Andyjr1515 said:

.....

2.  See where the broken end of the rod is in this pic.  Are you able to work out relatively accurately how thick the wood is here, including any thickening due to meeting the headstock?

 

My suggestions, to be thrown to my knowledgeable peers are:

a) If this area was never thicker, then the original rod was placing as much force on this spot as a modern trussrod would, providing the main body of the rod reaches at least this point.

b) Other than in this specific area, any cracking of the back strip is structurally insignificant

What do folks think?

Point 2 above is a key part of the solution.  Some measurements every cm along the the neck and channel for the first 7 frets or so would really help establish the profile and what room is available.

I am pondering the forces situation, my Physics degree is very rusty these days lol.

[3below]

4 minutes ago, Andyjr1515 said:

Yes - a valid solution. 

But a tricky rout even with experience and an absolute no-no for someone with no experience.  It's possible, though (see above) it doesn't actually need those extra steps.  We'll see what the other clever folks think

Totally agree, I would be making alignment jigs etc. to attempt this one.  Getting the board on correctly afterwards would also challenge me.  It would be my solution of last resort.  Far easier if we can get a rod in the existing location.

[Si600]

26 minutes ago, Andyjr1515 said:

a volute

Hurr-hurr, Volute...

[Si600]

Silly question, and probably covered by the above "last resort" option, but could the fingerboard be reattached sans truss rod and then go through the back of the neck to install a new one and fit a skunk stripe?

[3below]

1 minute ago, Si600 said:

Silly question, and probably covered by the above "last resort" option, but could the fingerboard be reattached sans truss rod and then go through the back of the neck to install a new one and fit a skunk stripe?

Eminently possible but again not for the 'faint-hearted'  I can see this considerably simplifying the jigs needed to do the routing.  The existing truss rod channel would act as a bearing guide for any routing.  OTOH the refinishing would increase significantly. 

[Andyjr1515]

2 minutes ago, Si600 said:

Silly question, and probably covered by the above "last resort" option, but could the fingerboard be reattached sans truss rod and then go through the back of the neck to install a new one and fit a skunk stripe?

Not a silly question, but exceptionally difficult without the right equipment and the new piece wouldn't match what is a full length centre splice.  Also wouldn't give you a structural advantage as the only critical point is at the nut end, and there, the thickness is the thickness...

[Jabba_the_gut]

8 minutes ago, Si600 said:

Silly question, and probably covered by the above "last resort" option, but could the fingerboard be reattached sans truss rod and then go through the back of the neck to install a new one and fit a skunk stripe?

Another option to consider and potentially doable but as @3below said, you would most likely need an assortment of jigs a the back of the neck I round, the route would need to be accurate, you need the router base to avoid the heel of the neck etc. It would also mean a complete refinish of the neck.

[Jabba_the_gut]

And that stripe goes all the way from one end of the bass to the other so lining up a skunk stripe of the correct width would be another challenge!!

[Andyjr1515]

Actually, though, following @3below 's suggestion of putting a full length fillet in the bottom of the slot: if there isn't already enough thickness at the nut (and there might be), there is a variation on his theme.

You could put a short strengthening/thickening fillet at the nut going back, say, just an inch.  That would raise the nut end of the trussrod (assuming modern) top face a mm or so above the neck face for a short length back from the nut.  You could certainly file or chisel a clearance slot in that short bit of the underside of the fretboard - and it wouldn't need to be overly accurate as long as it cleared the bit of the rod that was standing proud!

I think that could be plan B if the thickness under the nut isn't quite enough at the moment

Edited May 16, 2020 by Andyjr1515

[stewblack]

Hi guys, thank you all so much for your thoughts on this. I'm heading to the shed now and shall attempt to answer some questions when I get there. Andy's question about material removed from the nut end I can answer now. I scraped back a couple of mm from top and sides of the rod (before we embarked on this craziness!) as a first attempt to expose more thread and thereby have space for a washer. The (now snapped off) end of the rod had no useable thread at the tip so a washer essentially made it impossible to start the nut. Which is why I thought I might win by exposing a little more of the rod. I removed nothing from the underside.

[Aidan63]

fyi the plastic 'dark wood' tube at the top of the neck that finishes the truss rod hole on a Squier VM intrudes into the, much thinner than this, fret board by a good couple of mm under the nut, hence a very shallow nut slot on those

[Jabba_the_gut]

58 minutes ago, Andyjr1515 said:

My suggestions, to be thrown to my knowledgeable peers are:

a) If this area was never thicker, then the original rod was placing as much force on this spot as a modern trussrod would, providing the main body of the rod reaches at least this point.

b) Other than in this specific area, any cracking of the back strip is structurally insignificant

What do folks think?

I'm still thinking that a two way truss rod would put more force at the nut and heel compared to a single acting as that would seem to me to putting all of its force down the length of the neck to bend it. Just my thoughts as I've never tried this!

I like the idea of routing a channel in the back of the fretboard and gluing in a new wooden strip in the bottom of the fretboard to use a two way rod. I think this would give a little extra thickness at the nut providing some additional strength. What this would do though is raise the position of the truss rod adjust by 3mm  - would this the foul on the truss rod cover?

Edited May 16, 2020 by Jabba_the_gut

[stewblack]

2 hours ago, BigRedX said:

Out of interest how thick is the fingerboard?

1cm at thickest 8 mm at sides 

[stewblack]

1 hour ago, Andyjr1515 said:

See where the broken end of the rod is in this pic.  Are you able to work out relatively accurately how thick the wood is here, including any thickening due to meeting the headstock?

16.5mm at the paint line

slot here 9.5mm deep 

Edited May 16, 2020 by stewblack