I have been reading (and re-reading) Hiscocks's book "Make your own electric guitar". I have been spending some time looking over the chapter on routing and installing the truss rod. I know this has been beat to death somewhat but I have not found any discussions about "how to" and "why" (if anybody can provide a link to a previous thread it would be appreciated).

The book mentions several different types of truss rods and methods of installation. I am particularly interested in how to do a curved route. The best way to do this, obviously, is with a jig (which is mentioned in the book). This is the "how to" discussion I would like initiate. How do you do it? Can you provide any pics of the jigs that you use as well an a description of your process? Any tricks or knowledge you have learned from experience?

Another topic I would like opinions on is the curve used. The book mentions two different types of truss rod routing: a uniform curve (where the deepest point is the midpoint) and a more asymmetrical type (where the deepest point is more towards the nut). What routing type do you use and why? I understand the reasoning for both methods but I am interested in your opinions.

Again, if these discussions have already taken place please point me in the right direction and I will contact a moderator to have this deleted. I just couldn't find any that discussed these topics specifically.

The two different curves in compression rods are simply because of the design of the neck itself. A fender type neck needs a different curve than the Gibson style neck (i.e. angled headstock, straight headstock)

A jig for doing a curve is simply two rails on both sides of the neck that have the curve carved on them. Your router just slides on those rails.

To tell the thruth, it is so much easier to take a flat truss rod, I don't think many builders still use compression rods.

oh, so the curved truss rod routing is for compression rods? I'm going to have re-read that chapter then. good to know.

yeah it is. but like Phil says, flat routes are so much easier, just use a Stew-mac Hot Rod and you'll be set.

well I guess that answers my question(s). I'm glad I posted before I routed, I could have really screwed thing up!

I do plan on using the 24" Spoke Nut Hot Rod.

The two different curves in compression rods are simply because of the design of the neck itself. A fender type neck needs a different curve than the Gibson style neck (i.e. angled headstock, straight headstock)

A jig for doing a curve is simply two rails on both sides of the neck that have the curve carved on them. Your router just slides on those rails.

To tell the thruth, it is so much easier to take a flat truss rod, I don't think many builders still use compression rods.

A compression rod goes in a straight slot. It works by compressing the back of the neck, hence "compression".

The Hot-Rods that you can get from Stew-Mac are very slick. I highly recommend getting the accompanying router bit if you ever plan to build more than one bass. I ordered a 'traditional' stlye truss rod, and a Hot-Rod for my two recent build, just to see the difference. The Hot Rod install was very simple, and with the specific width router bit, was made in two passes down the router table to get the right depth. (which was deeper than the other rod, which may limit how thin your neck can be)

The other rod required a fair bit more trial and error as I had to get the width 'just right' by offsetting the 1/4" bit I was using and running the neck through the table several times to get the width correct.

About the only thing that required any thought at all was measuring where the end of the rod will be on your neck/fretboard so you can route out the access groove in the body for your wrench.

Have fun!

Jeff

I rout all my truss rod channels in a milling machine with a router mounted to it. It takes only moments to clamp the neck in. I also use the mill to make templates to pickups...its fast and easy to make perfectly square templates.

I route tr channels with a router and the guide up against the true edge of the neck blank. Quick and easy.

I rout all my truss rod channels in a milling machine with a router mounted to it. It takes only moments to clamp the neck in. I also use the mill to make templates to pickups...its fast and easy to make perfectly square templates.

interesting. I have access to a milling machine at work. I'll have to think about this.

I use a router table and a piece of MDF as a fence. easy and quick with not much setup time.

I rout all my truss rod channels in a milling machine with a router mounted to it. It takes only moments to clamp the neck in. I also use the mill to make templates to pickups...its fast and easy to make perfectly square templates.

Ok, I'm curious. Why mount a router rather than just use the mill head?

A compression rod goes in a straight slot. It works by compressing the back of the neck, hence "compression".As far as I'm aware, this is inaccurate. While this is possible to work, the rod has to be close to the back surface of the neck along its entire length, and I'm only aware of - possibly - Carl Thompson doing this.

Look at any fender neck with a heel-end adjustment. The rod end is far nearer the fingerboard than it is the back of the neck. If the rod were straight, it might in this case actually reside on the same side of the neutral axis as the strings- and would then help them to bend the neck forward, rather than fight the forward bow. This is clearly not the case.

A conventional compression rod is laid into a curved channel, and the backbow action is mostly accomplished by the the tension on the rod "trying to straighten the channel" - that is, it puts force towards the fingerboard at the middle of the rod, and away from the board at the ends.

Google Thaddeus McHugh to learn the difference between a compression rod and a bending rod...

I have no idea what a bending rod is, but a traditional truss rod, i.e. a compression rod was invented by Thaddeus McHugh a Gibson employee and they've been using these rods since then.
This is what we were talking about before. These things are bent inside a curve hole. The Gibson bend is a lot less steep as the Fender one but it's still there.

Here's a Frank Ford piece from frets.com explaining that.

http://www.frets.com/FRETSPages/Luthier/Data/TrussRods/trussrods1.html#Compression

I have no idea what a bending rod is, but a traditional truss rod, i.e. a compression rod was invented by Thaddeus McHugh a Gibson employee and they've been using these rods since then.
This is what we were talking about before. These things are bent inside a curve hole. The Gibson bend is a lot less steep as the Fender one but it's still there.

Here's a Frank Ford piece from frets.com explaining that.

http://www.frets.com/FRETSPages/Luthier/Data/TrussRods/trussrods1.html#Compression

From your link:
"The basic action of the standard adjustable truss rod is by compression of the back of the neck. When the nut is tightened, the back of the neck is compressed and causes the neck to bend backward. It is really quite predictable because the back of the neck has a much smaller cross-sectional area, so it compresses much more easily than the front. If the truss rod were mounted closer to the fingerboard it would have to pull harder to compress the back of the neck, but it could still do the job, because the fingerboard is very dense material and really resists compression.

I hope that makes sense. All adjustable rods work on the same principle. Compress one side, and something is bound to bend."

Notice no mention of a curved slot...

I'm not saying people don't put rods in a curved slot, just that when you do that it's not a compression rod...

That quote is short-sighted for several reasons.

First, let's lay out the principle of operation of a "pure compression" rod (not a "bending" rod, which as others have pointed out, is ordinarily called by most people a "compression rod"): There exists a virtual plane, referred to as the "neutral axis" (name derived from its 2-D representation). This is the plane on which, if the neck was bent by direct application of a moment (torque), similarly to what is done by the string tension, there would be no tension or compression. On one side of this plane ("neutral axis", NA henceforth) the wood will be in tension, and on the other it will be in compression.

The strings (in conjunction with the heel anchorage) create a force which is offset to the NA, and fairly parallel to it. This results in a forward bending moment, which creates "forward bow".

A pure compression rod acts (at least initially) only on the two points on the ends of the rod. The rod is in tension, and on the other side of the NA from the strings; this creates a pair of point forces, offset from the NA on the other side of the NA from the strings, which tends to bow the neck backwards, in opposition to the forward bow produced by the strings.

The farther a given force is offset from the NA, the more bow it will produce. This offset distance is a result of the location of the applied force, and the location of the NA.


Now, concerning the assertions of the quoted material:

1. True, the neutral axis is shifted forward towards the fingerboard by the shaping of the back of the neck. However, not accounted for here is the resultant fact that if you like a flatter rear contour, you lose some of this trait.

2. True, a stiff fingerboard combined with a less stiff neck shaft results in the neutral axis being shifted towards the fingerboard. This reduces the effect of the strings, and increases the effect of a pure compression rod, because the force offset distances are adjusted by the amount of shift of the NA. However, not accounted for here is the fact that this stiffness inequality is fairly significant in a rosewood/mahogany neck, such as is found in acoustic guitars, mandolins, etc.; it is less so in a rosewood/maple neck, such as is commonly found in basses and electric guitars; and the effect is entirely absent in maple/maple necks.

3. Also unaccounted for is the effect on NA position due to fiber or steel stiffening rods. Carbon fiber rods can significantly "draw the NA to themselves," so a pure compression rod would have to be nearly out of the neck in order to have any significant effect.

I used LMII's double action rod and when the neck was still sqare i lined it up one a router table and sent it thru. Pretty strait forward although routing is still something im not comforatable doing.

Hiscock, in his book, has two drawings in the Truss Rods chapter: one of a Gibson style rod; the other of a Fender style rod. It is clear in both drawings, that the truss rod channel is curved.

Hiscock goes on to discuss how to fit the Gibson style rod and explains it is fitted into a curved channel. He also states that not much curve is required for the channel and explains the impact of a channel with too much curve for this type of rod.

... and the point of me quoting the frets.com article was to look at the picture that shows the slight curve under the fretboard.