Guitar Neck Wood
Guitar neck wood for a classical guitar must be stable and strong without being overly heavy. The traditional choices have been mahogany and Spanish cedar. Both are very stable and have a good strength to weight ratio. The main difference is that you will find that mahogany is a bit more dense then Spanish cedar.
On steel string guitars the weight of the wood for the neck is not as much of a concern. I have seen walnut, maple, and even nara used with success. For a steel string guitar strength and stability are everything since the string tension on a steel string guitar is far greater than that of a classical guitar.
The neck and the top directly absorb all tension of the strings. Non-traditional guitar neck wood is being used today with success. To ensure that your instrument will not develop severe problems as it ages the guitar neck wood should have certain characteristics. Consequently, you must consider wood selection seriously .
Choosing Wood for the Neck
Stability is Everything for Guitar Neck Wood
One of the most important features of the neck is stability. The neck should not warp, twist, cup or bow as it ages. It needs to be able to stand up to the tension of the strings throughout its life. If the right cut not selected from a piece of wood it may consequently bow or cup after it is re-sawn.
Reasons for cupping and twisting have to do with the way the tree grew and where in the tree the neck blank came from. A piece of wood cut from a tree with a slight bow to its trunk will result in a piece of wood that will want to retain that shape when it is thinned down. This will cause problems down the road and is to be avoided. You must learn how to detect these types of flaws in wood and avoid selecting wood with these kinds of flaws for necks or consequently, your guitar will develop problems.
Check for Tendencies
You must check for tendencies as you prep the neck blank for use. You will mill the neck blank making sure to take some wood off on both sides, but leaving it thicker than you need. Then you must let it sit for a few days. You will want to come back and put a straight edge on it to see if there is any bowing or twisting. If there is a bow of more than 1/32 and of an inch I would consider finding another piece for the neck blank. Should it be twisted at all, I would not use it for the neck blank.
If the changes have not been too severe ( no more than 1/32″ in the middle) you can use this piece for the heel stack. The pieces for the heel stack should only be about 5 inches long. The bowing or cupping will be minimal over this length and be considered negligible. Therefore, as you glue pieces on top of each other no movement is likely.
Strength and Runout
The wood for the neck blank should also be strong. To assure the neck is strong you need to select a piece that has minimal run out.
You can see run out in the side grain of the neck blank ( see photo on right). The grain lines should run parallel to the surface. Perfectly parallel grain lines are difficult to find so it is likely that the lines will angle toward the edges. So you want to make sure that if the grain lines run from one face to the other, they do it over a distance of 5 inches or more.
Should the side grain run from top to bottom in a short distance, say an inch or two, this is what is known as short grain. Short grain is weak to shear force. You do not want to use any piece of wood with short grain because it is not optimal for strength. The strings will generate a good amount of shear force, therefore the neck wood should have as little run out as possible.
Mahogany or Cedar
Mahogany is more dense than Spanish cedar and generally a bit darker in color as seen on the right, but both carve equally well. The difference in density will have an effect on the sound of the instrument. I find that mahogany, because of its weight, generally produces an instrument with deeper basses. Spanish cedar on the other hand has more of an effect on the trebles and help make them very clear.
This makes selecting one or the other a trade-off to some degree. Meaning you are giving something up to get something else. In order to minimize the trade-off things can be done to the treatment and selection of the soundboard to compensate for this.
Wood for Fingerboards
Guitar fingerboards are typically made of Gaboon ebony. You will occasionally find some fingerboards made of some type of rosewood. Higher end guitars tend to use ebony exclusively.
Ebony is very dense wood and has excellent wear resistance. Since the fingerboards are constantly being hammered on, and fingers sliding around on them, ebony is an excellent wood choice. It will hold up to this abuse very well over time. It has been used on all types of stringed instruments for hundreds of years. Stick with what works
Good ebony fingerboards are becoming harder and harder to find. Jet black quarter sawn pieces of ebony for fingerboards are rapidly becoming a thing of the past. If you can find a good quarter sawn piece today, you more than likely will have to settle for some streaks. If you are forced to choose, always choose visual flaws over inferior cuts of wood. I find that some types of rosewood will also work for fingerboards as well. Macassar ebony will also work but you may find it difficult to locate in the thicknesses needed.
If given a choice of a bad piece of ebony and a really good piece of an alternative wood such as a rosewood or Macassar ebony, I will choose the good piece of alternative wood every time when it comes to fingerboards.