Building Your Own Custom Truss Rods

[Bruce Johnson]

Reminder for those with WBO 2018 TOW - one stand of that (24K) is equivalent to Bruce's 4 strands of (IIRC) 6K

Actually, my current roll of TOW is 12K, so I put a total of 48K of strands in each of these necks. It may be overkill, but these are 6-string basses with no additional stiffeners added to the necks. I decided to be cautious.

I normally use 2 strands of 12K in most guitar and bass necks.

 

[BishopJP]

Is there a point where adding more strands of CF TOW is a disadvantage?
I'm guessing there is a point of diminishing returns and a limit to how many strands you can physically fit into the neck; but is there a point when "too much" TOW can cause problems?

 

[T_Bone_TL]

Generally even a completely CF neck isn't "as much as you can cram in" - for good engineering and economic reasons they are more of a tube around either airspace or a low-density filler. @Gilmourisgod mentions an early Steinberger as an example of a totally stiff neck with cast-in relief and no truss rod from time to time. So if you expect the neck to actually be adjustable with a rod, yes, there's apparently such a thing as too much. Presumably if you take the approach of a built in relief curve you just make the neck immovable and then too much is a matter of balance. And perhaps economics. CF properly deployed allows for light, stiff structures, but a "solid neck of CF" is more like a solid neck of heavy plastic, with CF doing almost nothing mechanically in large parts of it.

 

[BishopJP]

That makes sense.

In the particular application of the CF "backstrap", it seems to me that you would hit the point of more CF "doing nothing mechanically" before you get to the point of the neck being immovable?

 

[Bruce Johnson]

That makes sense.

In the particular application of the CF "backstrap", it seems to me that you would hit the point of more CF "doing nothing mechanically" before you get to the point of the neck being immovable?

Yeah, that's it. In the backstrap application, a single strand of 6K TOW is probably plenty to do the job. The key thing about the carbon fiber stranding is that it doesn't stretch under load. At all. I don't remember the numbers offhand, but you can apply many hundreds of pounds of tension to a 6K strand and the stretch will be a few thousandths' of an inch.

That's how we use it as the backstrap: as a tension strap. A slot filled with epoxy surrounding some TOW will not stretch at all under load. If we filled the slot with just epoxy, no CF TOW, the epoxy would stretch at about the same rate as the maple. The CF TOW prevents the epoxy from stretching, and the epoxy bonds over its full length to the walls of the slot. That keeps the maple at the back of the neck from stretching, which prevents 12th fret kink/Ski Jump.

So, adding more strands of CF TOW isn't likely to reduce the stretch any more. It's already almost nothing. And it isn't going to increase the stiffness of the neck very much. If the back of the neck is rigid and doesn't stretch, then any bending of the neck happens by the fingerboard and wood in the front compressing. Making the backstrap thicker doesn't change that.

But, adding a couple of extra strands of CF TOW adds almost no weight to the neck. So, it's a little extra security for no real penalty.

 

[BishopJP]

Yeah, that's it. In the backstrap application, a single strand of 6K TOW is probably plenty to do the job. The key thing about the carbon fiber stranding is that it doesn't stretch under load. At all. I don't remember the numbers offhand, but you can apply many hundreds of pounds of tension to a 6K strand and the stretch will be a few thousandths' of an inch.

That's how we use it as the backstrap: as a tension strap. A slot filled with epoxy surrounding some TOW will not stretch at all under load. If we filled the slot with just epoxy, no CF TOW, the epoxy would stretch at about the same rate as the maple. The CF TOW prevents the epoxy from stretching, and the epoxy bonds over its full length to the walls of the slot. That keeps the maple at the back of the neck from stretching, which prevents 12th fret kink/Ski Jump.

So, adding more strands of CF TOW isn't likely to reduce the stretch any more. It's already almost nothing. And it isn't going to increase the stiffness of the neck very much. If the back of the neck is rigid and doesn't stretch, then any bending of the neck happens by the fingerboard and wood in the front compressing. Making the backstrap thicker doesn't change that.

But, adding a couple of extra strands of CF TOW adds almost no weight to the neck. So, it's a little extra security for no real penalty.

Well, I guess 3 strands of 24k TOW is overkill then...
I guess I can scale it back a bit on the next build!

 

[dazmond]

One thing I am having a hard time understanding is the curved channel. The router jigs on this thread looks like they are dead straight at the heel end and then just curve up towards the nut anchor, and Bruce does talk about having a straight slot from the 5th fret to the heel. Wouldn't that make most of the truss channel at max droop depth? That doesn't seem very curved to me.... What am I missing? I expected the whole channel would be a curve, like this picture of a warwick, or pictures of where Bruce is explaining droop using a fender cutaway as an example.

L

Thread 'Bruce Johnson Truss Rod Droop'

Nov 24, 2023

Hi,

Building my first guitar necks (vintage telecaster style) and i'd like them to have single action vintage truss rods. I've researched a bit on the truss rod channel channel and curve and found Bruce's posts here. My Luthier also referred me to Bruce's posts here when I asked him about truss rod curve

The one thing I'm not quite understanding is when we say Truss Rod "droop" of 0.180" and fenders and gibson typically have around 0.12" - 0.15" droop what exactly is that referring to? If I look on typical tele neck plans with the curve, it looks like the deepest part of the curve is...

• leemoore
• Replies: 9
• Forum: Luthier's Corner

 

[Bruce Johnson]

One thing I am having a hard time understanding is the curved channel. The router jigs on this thread looks like they are dead straight at the heel end and then just curve up towards the nut anchor, and Bruce does talk about having a straight slot from the 5th fret to the heel. Wouldn't that make most of the truss channel at max droop depth? That doesn't seem very curved to me.... What am I missing? I expected the whole channel would be a curve, like this picture of a warwick, or pictures of where Bruce is explaining droop using a fender cutaway as an example.

L

Thread 'Bruce Johnson Truss Rod Droop'

Nov 24, 2023

Hi,

Building my first guitar necks (vintage telecaster style) and i'd like them to have single action vintage truss rods. I've researched a bit on the truss rod channel channel and curve and found Bruce's posts here. My Luthier also referred me to Bruce's posts here when I asked him about truss rod curve

The one thing I'm not quite understanding is when we say Truss Rod "droop" of 0.180" and fenders and gibson typically have around 0.12" - 0.15" droop what exactly is that referring to? If I look on typical tele neck plans with the curve, it looks like the deepest part of the curve is...

• leemoore
• Replies: 9
• Forum: Luthier's Corner

Go back to page 2, post #85:

Post in thread 'Building Your Own Custom Truss Rods'

May 11, 2024

While not exactly 100% on-topic, it will become more so when you start discussing your DASR design in earnest:
You’ve discussed what you have found to be the ideal deflection or “droop” for your single-rod truss rods a number of times and that it doesn’t matter what the rod length is, particularly. In light of that, what sort of jig are you using to cut your curved-bottom truss rod slots? Is it a universal (adjustable) jig that adjusts the curve to match the slot length or do you use separate jigs that are bespoke for each length? And is it a router jig (I assume that it is)?

Hey...

• Bruce Johnson

• 

Here's the key part:

If you look close at this fixture, the side rails curve down from the headstock end to the middle, but then stay level out to the end of the heel. This neck is getting a DASR truss rod with the carbon fiber backstrap. I'm cutting the slot to curve down into the Droop on the outboard half, from the nut to about the 5th fret. The rod gets epoxied in, pressed down tight against that outboard half of the curved slot.

But, from the 5th fret to the heel, the slot stays straight, parallel to the top surface. The rod curves back up to the surface at the anchor. It has the whole Droop curvature, 0.180" deep at the 5th. The long narrow wedge gap under the rod, from the 5th to the heel, is filled with epoxy and the carbon fiber TOW strands. That's the Backstrap. Cast in place, filling that space. The Backstrap prevents the back of the neck, from the 7th to the heel, from stretching over time. As in 12th fret Kink aka Ski Jump.

Summary: The straight section on the inboard end of the neck is to allow space for my carbon fiber backstrap. If I were building a neck without the backstrap, then I'd cut the channel with the full curve. But with the backstrap in there, the truss rod still ends up curving up at the inboard end, forming the full "droop".

 

[dazmond]

Thanks, Bruce. I have read over these details a number of times, but my thoughts weren't quite lining up. I didn't want to assume I was reading it correctly, as the jig pictures were not what I had initially imagined. I think your summary solidified it for me.

 

[Bruce Johnson]

Thanks, Bruce. I have read over these details a number of times, but my thoughts weren't quite lining up. I didn't want to assume I was reading it correctly, as the jig pictures were not what I had initially imagined. I think your summary solidified it for me.

One more technical note about that: At the inboard end, the rod is pulled up into the Droop curve by the mechanical position of the anchor/adjusting head. Then the long wedge-shaped gap underneath is filled solid by the epoxy, with the carbon fiber in it. The epoxy fills all the space under and around the rod, forming the curved slot. There's no air gaps or clearance anywhere inside the neck.

 

[dazmond]

Couple general questions for anyone that can answer:
#1- accidentally bent my rod before I even started trying to thread, do I need to buy a new piece? I bent it back and it's nor horrible, but I can tell where it happened.

#2- borrowed a die set from my in-law and was unable to even get anything started. I did chamfer the end. It's old/dull/cheap/not right material? I can't find anyone else I know that has a set and everything local(Canada) is very expensive. I wasn't intending to invest $100 in a potentially 1 time job. Will a cheap one get me through threading 2 ends of a rod?


Hopefully the brass part goes smoother, I'm a little nervous now.

 

[Slidlow]

Couple general questions for anyone that can answer:
#1- accidentally bent my rod before I even started trying to thread, do I need to buy a new piece? I bent it back and it's nor horrible, but I can tell where it happened.

#2- borrowed a die set from my in-law and was unable to even get anything started. I did chamfer the end. It's old/dull/cheap/not right material? I can't find anyone else I know that has a set and everything local(Canada) is very expensive. I wasn't intending to invest $100 in a potentially 1 time job. Will a cheap one get me through threading 2 ends of a rod?


Hopefully the brass part goes smoother, I'm a little nervous now.

Where are you?

 

[dazmond]

Where are you?

Saskatoon, Canada

 

[Slidlow]

Saskatoon, Canada

Ahh, I’m in Ontario. Too far to help.

 

[dazmond]

Ok, apologies about the panic. I was able to find a high speed die on amazon for $20 ish. I swear I searched everything multiple times and the options were not coming to me. The question will remain as a reference to others though, will a cheap or non high speed die get someone through putting threads on one rod?

 

[dazmond]

Another question about anchor location: I'm building a multiscale bass and my instinct is to put the anchor right up at the nut on the middle string, is this good? Or maybe level with the nut at the G string?

 

[Bruce Johnson]

Another question about anchor location: I'm building a multiscale bass and my instinct is to put the anchor right up at the nut on the middle string, is this good? Or maybe level with the nut at the G string?

I usually locate the truss rod anchor about halfway between the nut and the first fret.

 

[Bruce Johnson]

Ok, apologies about the panic. I was able to find a high speed die on amazon for $20 ish. I swear I searched everything multiple times and the options were not coming to me. The question will remain as a reference to others though, will a cheap or non high speed die get someone through putting threads on one rod?

Yes, you are better off buying a single good quality High Speed Steel threading die, than using the die from one of those cheap sets. You can use one of the cheap dies, slowly and carefully, but they don't cut as easily or smoothly.

With the cheap dies, you have to cut interrupted; a half-turn forward, stop, back up a quarter-turn, a half turn forward, etc. The good quality die will cut with continuous turning, no need to stop and back up.

 

[dazmond]

Bruce, any thoughts on the bent rod situation? (snagged it tightening the vice and bent about it 45°, straightened it out pretty good but it "remembers" where it happened.)

 

[Bruce Johnson]

Bruce, any thoughts on the bent rod situation? (snagged it tightening the vice and bent about it 45°, straightened it out pretty good but it "remembers" where it happened.)

That shouldn't cause any problem. Straighten it out as well as you can.