Neck Construction for Stringed Instruments

February 26, 2023

Neck Construction for Stringed Instruments

One of the most difficult pieces of the acoustic, classical guitar and ukulele construction puzzle is precise construction and adjustment of the instrument neck. The neck has several important duties to perform:

  • Provide accurate and consistent intonation for the instrument
  • Allow the guitarist to easily play the instrument — thinner necks tend to provide easier and much faster action.
  • Resist between 100 and 200 pounds of tension placed on it from properly tuned strings for guitars. Much less tension for ukulele necks.
  • Allow for easy adjustment for changes in atmosphere
  • Provide just the right "balance" so the instrument is not "neck-heavy" due to heavy construction materials.
  • Prevention of twisting due to its long, thin nature
  • Allow for easy adjustment to bring it back to the correct "neck relief" as the forces of nature and usage take their toll.
  • Contribute to the tone and volume of the instrument, by vibrating with the entire instrument.
  • Provide grace and beauty to a finished instrument
  • Provide a firm foundation for the fretboard, nut and tuning machines.

 

Wow, that is quite a list, and some people just think of the guitar neck as a "handle". Not so!

In order to control all of these things and do them well, there are many considerations we have to weigh before we buy our neck materials and actually construct the neck.

Here are some of items that need to addressed before the neck construction begins:

  • Species of Wood
  • Grain direction
  • Consistency of Grain
  • Weight of Wood Materials
  • Appearance of the Wood as it relates to the back and sides
  • Reinforcement Medium
  • Neck Adjustability (Steel String Acoustic Only) Adjustable truss rods vs fixed reinforcement options
  • Supplemental Static Reinforcement - Hardwoods, Laminates such as Ebony, Maple and Carbon Fiber and Aircraft Aluminum
  • Neck Construction
  • One Piece vs. Laminated Wood Neck.
  • Mechanical Neck Attachment (Steel String Acoustic) Bolt-On vs Fixed.
  • Type of neck joint: Mortise & Tenon or Dovetail.

 

Neck Reinforcement:

Is it really necessary to reinforce the neck of a Ukulele? Usually not because of the short length of the neck, the width to depth ratio of the wood and the low tension of the strings, and necks on these small instruments cause few problems. Probably the biggest concern is change in temperature and humidity, which can warp the wood. To combat these environmental conditions, laminate the wood of the neck and consider using higher strength wood in the center of the neck or even a strip of Carbon Fiber.

Dimensions of the neck

This is where fractions of inches can make a BIG difference in the way our instruments play. We need to be concerned about width at the nut and at the body, string spread at the nut and the saddle and neck thickness to provide just the right balance of structural integrity and fast action.

All of these elements have an equal roll for both the initial construction, and contributing to the longevity of a well-constructed acoustical instrument neck and we will explore each of these elements in detail. 

Grain Direction For Necks

For the luthier just starting out, the decision of which species of wood to use for the neck can be very confusing. So many choices. So many decisions.

There are a several important aspects you should consider when selecting your neck wood:

The physical properties of wood that resist bending are both parallel to the grain and perpendicular to the grain. These properties can vary widely depending of the wood species. Generally speaking, many of the hardwoods exhibit excellent bending qualities in both directions. 

QuaterSawn Wood:

Typically, wood that is quarter-sawn is the strongest and resists bending and twisting the best as a single-piece neck. Wood that is quatersawn means that the lumber is cut so the wood grain looks vertical or nearly vertical when viewing the end grain of the wood. Note that even quarter-sawn wood is often not perfectly vertical and tends to run-out at one edge or the other. Quarter-sawn wood resists upward bending the best for one-piece neck construction, but not necessarily so with multi-laminated neck construction.

Bias Cut Wood: 

Oftentimes quarter-sawn wood is either not available for certain wood species or it is extremely expensive. The next option is wood that is cut on the bias, which means the grain runs at an angle when viewing the end grain of the blank. Since it is economically not feasible to make every cut of wood from a log perfectly quatersawn as there would be a tremendous amount of waste, the logs are usually cut into 4 or more pie-shaped pieces and each of these pieces are cut perpendicular to the grain. The result is the few pieces of wood that are cut directly from the center of each segment have nearly vertical grain and as the cuts progress outward to the edges of the segment, the grains becomes increasingly more biased.

Flat-Cut Wood:

This type of wood is cut in such a manner that the grain runs more horizontally than vertically, so it is an angle that is shallower than 45 degrees. This is how most hardwoods that are readily available are cut, as these results in the greatest yield from a log. Flat cut (also called slab-cut) wood resists sideways bending the best.

Therefore, which type of cut should we use for our instrument necks? The answer is that all of them can be used, and with the exception of quatersawn wood, we have to do some additional prep work to make them suitable in our neck construction:

Look at the diagrams on this page as a reference. When the grain runs at any angle and that angle is rather consistent for the entire cross-section of the neck, there will be  tendency for the neck to twist, or warp and no longer be truly straight. The best way to combat this twisting action is the construct the neck in such a manner in that the grain for each half of the neck "opposes" each other, which is many times referred to as "book-matched" grain. But in this case we are referring to the end grain of the wood and not the surface of the neck.

So as one half of the neck will tend to bend or twist in one direction, the other half of the neck will provide an equal resistance in the opposite direction and you will have an equilibrium of force in the neck, resulting in a neck that is extremely strong and resistant to bending forces. In most cases, there is much more structural resistance in a neck constructed in this manner, which is much like glued laminated beam construction for structural wood.

Additional elements can be used to resist both bending from string tension and twisting action from atmospheric changes. These options are explored in the articles on

  • Tempered Aluminum Neck Reinforcement
  • Carbon Fiber Neck Reinforcement
  • Carbon Steel Neck Reinforcement
  • Wood Laminate Neck Reinforcement

Note: A few months back I received pictures of an acoustic guitar that my father had constructed in the early 1970's. The owner said he just purchased the guitar for the original owner and couldn't believe that the neck was still dead-on straight after 50 years. My father used aircraft aluminum to reinforce this neck.

Neck Assembly: 

Now you should assemble the neck. As mentioned above, an assortment of wood can be used, but make sure what you choose is a good, strong hardwood. Cut the portion to be used for the neck right down the center and flip the pieces so the grain is opposed on each half, or is book-matched. Add a center strip if desired and glue it up, plus any additional reinforcement medium such as Hardwood Laminations. After the neck assembly is dry, square it up and you can use the Neck Assembly Jig to run it through your band saw to cut the exact scarf joint angle. Do the same with the headpiece. Cut the headpiece to desired thickness. To help you with this operation, we have put together another tutorial on neck construction.




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