Types of Linings:
First of all let’s clear up the terminology here. Some refer to these as Linings, and some refer to them as Kerfing. Neither is wrong, but I will always refer to them as linings because not all linings are kerfed. There are basically 3 types of linings that we commonly use for stringed instruments.
This is the typical lining that you will see on most Acoustical Guitars and Ukuleles – Both factory made and handmade. It consists of either of two types of wood and these are usually Basswood or Mahogany. The lining will be serrated or kerfed to allow easy bending around the upper and lower bouts and the waist.
Usually two profiles are used for the lining. The triangular, which is about 1/2″ to 3/4″ high x 5/16″ wide at the bottom tapering to about 1/32″ at the top. The second lining is more rectangular in profile, being about 1/2″ to 3/4″ x 5/16″ with the exposed edge receiving a radius of about 1/4″.
Both of these are acceptable for both top and bottom plate attachments. Be sure to check the purfling and binding heights and widths to make sure they do not extend the router channels beyond these dimensions or you will find the Sitka Spruce top lying in the bottom of your inside form!
Solid lining is most often used for classical guitar lining and it is used for attachment of the backs to the sides of these guitars. It is about 5/8″ high x 1/8″ or so wide – again the width depends on your decision for purfling and binding sizes. The exposed edge of the binding is radiused, usually about 1/16″ to the full width of 1/8″.
Materials for Classical Guitar linings vary from luthier to luthier, but here are the more common picks and some of my favorites:
Basswood: Bright white – Looks great, no grain to deal with, bends easily and provides a nice solid structural tie between the back plate and the sides.
Genuine Mahogany: Another of my favorites. Bends easily, nice color and very good structurally.
Side Wood Match: This is used less frequently, but is still a good option. The side wood that is used on your Classical Guitar is usually very dense. Be cautious with this though as this wood may be difficult to bend – especially that nasty waist curve. Also you have to be Very Vigilant that you have cleaned all of the wax and resin residue from the line to make a proper glue joint.
Separate Glue Blocks – Both Acoustic and Classical – Top Plate Only:
I have used this method for both Classical and Acoustic guitars. I would say that on about 60% of my Acoustic Guitars are built this way and I reserve this method for only the higher end guitars. It is more time consuming, but I feel you get a better sounding instrument.
Basically the lining is shaped very similar to the Triangular type listed above, but slightly larger. The size I use is about 3/8″ x 5/8″ x 1/2″ long. They are all separate and hand glued to the top and side wood. This eliminates stress and allows for a free-floating top. The blocks need to be “hand fit” around some of the curves, so this can be a tedious project – but well worth the effort. To minimize the hand fitting you can also make the blocks shorter around the tighter curves, but it is more difficult to place them properly.
Materials: I use either fine grain Sitka Spruce or Cedar. With Cedar, I make the blocks a little over-sized to compensate for the reduced structural capacity of Cedar. An extra 1/16″ in width and 1/8″ in height will do.