Fender's truss rod curve?

[Glen Canaday]

Hey all,

It's been a very long time since I was last on this forum, and when I was, I didn't post much. I read a lot, though.

I'm curious about the purpose behind Fender's truss rod being curved. It's closer to the back of the neck in the middle, and closer to the front at the ends. Other rods I've seen installed at laid in straight. Is Fender the only commercial maker to do this, or is it more common than I think?

--GC

[Peter Wilcox]

It's a single action rod. When it is tightened it tries to straighten out, giving the neck a back bow if no string tension. The string tension counteracts this, straightening the neck. It's no good on a neck with forward bow.

I don't know what makers use this besides Fender.

[Mark Swanson]

Traditional Gibson rods are made that way too.
Some straight rods, like the Martin rods, are not double-acting but work in a different way. They consist of a rod on a channel and by making the rod smaller (tightening it) it bows the channel against the string pull.

[Glen Canaday]

That's the way I'd assumed the Fender rod to work, too.

So, it's curved in order to give it a little more room to work that a straight rod normally wouldn't have. It straightens out while a straight rod just compresses its side of the neck. Makes sense.

How do they route the channel? I've tried curves like that with hand tools and it's not simple... is it a curved insert at the bottom of the channel? The X-rays I've seen didn't show much beyond the curved rod.

--GC

[Peter Wilcox]

So, it's curved in order to give it a little more room to work that a straight rod normally wouldn't have.

That's not the way I'd put it. It's a relatively tight fit after gluing in the skunk stripe. It works by putting pressure on the neck as it straightens out.

[Peter Wilcox]

That's the way I'd assumed the Fender rod to work, too.
How do they route the channel?

I've heard of using an insert, but never done it

I made a jig to route the curved channel in the neck The router rides on the radiused boards inside each side of the jig, and cuts the channel (in the upside down neck blank) with the same radius. Pretty rough jig, but it did the job.

[Glen Canaday]

I hadn't thought of a curved jig, but then I don't have an electric router. The only router I have is a Mills Falls #67, and that needs some restoration.

I might have to buy a plunge router.

[John Catto]

So far as I know Fender always used the curved truss-rod route. Gibson's in the 50's were straight but angled much deeper towards the neck/body joint, this is easy to confirm by looking at the depth of the maple "filet" visible in the neck pickup cavity (and the experience and knowledge of luthiers who've renecked or replaced the truss rod in 50's guitars). I have a suspicion that the curve is something that Fender had trouble getting right at least at the start of using Rosewood boards. One of the Fender History books (sorry I forget which one) states that Fender switched from the 59-61 Slab Rosewood fingerboards to the curved "veneer" boards because they just couldn't get the truss rods to work reliably with the slab board (something worth remembering if you're under the misconception that a rosewood board is somehow softer than maple). I've also seen a number of Custom Shop guitars (made to 50's specs) where the trussrod just plain didn't work properly but didn't appear to be broken. On the other hand all those straight rods used by Gibson in the 50's continue to work fine.

While using an insert to generate the curve would certainly work you'd better keep a firm eye on the neck depth since you'd be removing wood close to the back of the neck all the way along, LOTs of potentional for error there.

[John Catto]

I should add since I can't reedit that post now that Gibson switched to a curved trussrod in 1960 loosly coinciding with their move to a thinner neck profile.

[David King]

I start with a center deflection = to the rod diameter or about .190" (5mm), I tape the bowed rod to the side of my neck blank and chart out the desired depths from the anchor to the nut, resting the lowest point of drupe about 1/8" from the back of the neck (in it's final thickness *NOT* in it's rough form).
I then take a strip of maple about 1/2" thick and 3" wide and about 8" longer than the rod and force the same bow into the stick by screwing the ends down to a section of solid 2x4 ( or 4x4) with a pencil squeezed in the middle. I then scribe a straight line along the edge on the bowed maple strip that's about 3/16 below the highest point where the pencil is located. This straight line should exit the top corners near each end of the stick. Those exit points should be about the same distance as the length of your truss rod. If the points are too close together increase the bow in the stick (by tightening down the screws on the ends or using a fatter pencil in the middle) until you get the same length between your exit points as your truss rod's length. Now draw a second parallel line about 1/16" below the first or about 1/4" below top center of your bowed stick.
Now gently wedge in addition sticks every 3-4" or so along your bowed stick and tack them in place with tape so they can't move around or fall out.

Next, plane or jointer or sand the top off the bowed stick off until you hit your second line (but not your screw heads which you took the trouble to countersink first). The support stickers you tacked in place will maintain the "fair" curve in the stick as you thin it (and weaken it in the center).
You can now rip this long 1/2 hour-glass shaped stick down the center and use it as a router depth guide when routing for your curved rod. You'll want to slide it fore and aft on the neck blank until it's thicknesses line up with the depths of the rod you taped to the edge of your neck blank.

No doubt that without pictures I'll have lost everyone by this point. Sorry about that.