I notice that some of the early Capri's use a single truss rod rather than the now common twin rod set up. Given how slim a Ric neck is it seems like a lot of material to route out of the neck!
Recently I made my first small "hands on step" into understanding the world of guitar construction by removing the fret board of a cheapy acoustic, and I was amazed at how flexible the neck was, once the fret board was off . Talk about flimsy
I understand the theory of two rods providing the advantage of greater adjustability, by being able to compensate for twist along the neck. However the two routed channels must surely mean that the fret board is asked to do a lot in terms of resisting string force even if it is in compression...surely?
Do you think the decision of RIC to move toward the twin rod arrangement's (old and new style rods) to be really an overall benefit, in terms of adjustability at the expense of structural strength? Also, are the new style rods smaller in dia to leave a bit more wood in the neck, my mid 90's 360/12's rods look like 1/4" stock?
Well, it would count for something, considering the three forces acting on the neck (tension, compression, and "torsion", or torque), if the steel rods were bonded into the wood of the neck so that (theoretically, at least) they became monolithic with the neck wood itself. In actuality, were this to be the case, the shear strength of the bonding agent would have to be taken into account, along with its service life.
Also, in actuality, were the rod to be bonded to the neck, its efficacy as being adjustable would be greatly reduced. The same applies to a dual rod setup.
But the rods lie loose in their channels. This is because they must be free to bend (in the case of old style "hairpin" rods) or compress in a curved channel (in the case of new-style rods) in order to press upon the top and bottom walls of the channels and nudge the neck into a shape to counteract the tendency of the tensioned strings to pull the neck into a bow shape.
A neck without a fretboard (in the case of a Rick, known for its slim necks--the older the guitar the slimmer the neck, too!) is very, very weak and fracture prone. What gives the neck--with or without truss rods--its strength is the fretboard that's bonded to its front surface. This adds immense strength with regard to all three forces mentioned above. And, though it may sound strange, removing the material in order to create the truss rod channels actually increases the neck strength, up to a point, of course--this wood, after all, not titanium.
It's an accepted, proven fact that a tube with a reasonable wall thickness is stronger in its ability to resist twisting and bending forces than a rod of the same thickness. Why? Because by making a tube--essentially a hollowed-out rod--you add another surface which resists force in the opposite manner from the face of the tube. Nearly twice as much surface area, in other words, and when one face is being compressed in an attempt to bend it, the face on the other side of the metal is being stretched. (this is why airframes and race car space frames use tubing, not rod, for linear members.)
This is much more efficient in a dense, ductile material like metal alloys, than it is with wood, but there is still enough of this effect to make a neck with a truss rod channel stronger after the channels are cut--provided the neck (in effect a wooden tube) is completed by bonding the fretboard into place.
Why two truss rods? To provide another dimension of adjustability and to counteract twist--provided the rods are properly and sensitively adjusted. Improperly adjusted, they can actually cause twist over time.
I hadn't considered the "tubular" strength part....
Besides the obvious cost I wonder why no one other than RIC seems to use the twin rod setup. I dont think I've ever seen any of the custom guitar makers (big $ instruments) using it either.
I like that Ricks seem to have been one of the most inovative makers, but that seems largely an historical observation on my part. Why not route out and fit two composite strips into the neck and use a single truss rod between them, that would enable a super thin neck profile?
Great technical question, and great resonse from Paul.
To answer your much simpler question, I believe Hamer use dual truss rods in their 12-string basses (and prrobably their 8-string counterparts), to compensate for the added tension. There are some boutique bass makers out there, such as Alembic, who also use a dual truss rod system.
"I don't want to sound incredulous but I can't believe it" Rex Mossop
Using the twin rods in a bass makes a lot of sense to me. After a ric guitar some of those bass necks feel lick a fence post to me. I'd love to try out one of those 8 or 12 string basses
While were talking about truss rods....I just read this morning that Martin had to stop using steel rods altogether during the 2nd world war as the steel was needed for the effort. In place, they glued in a strip of ebony.
