Bending Guitar Sides
Guitar making borrows most of its methods and techniques from woodworking. Many of the techniques I use in guitar making I have adapted from my days of furniture making. Almost any technique will work well if executed properly.
There are basically two methods guitar makers use to bend the sides of their guitar's. Regardless of the type of guitar making involved, both methods will work. They will work equally well on classical guitars as well as steel sting guitars.
The most common method used in guitar making to bend sides is similar to steam bending in furniture. The wood is first moistened with water and then applied to a heat source( as seen in photo on right) and slowly shaped by gently adding pressure to the wood forcing it to bend. In this case the heat source is typically an adjustable electric side bending device as shown in the photo. This method is typically done on guitar sides that are between .100" - .125" in thickness. This method takes some time, and in the end is usually not that accurate. Applying water to wood is also almost never a good thing with any wood that must adhere to specific dimensions. If this method is used make sure the wood is allowed to return to EMC (equilibrium moisture content) before use. Also, using a heat pipe as the heat source for this method is not safe and is not recommended. The amount of heat is hard to control and the presence of an open flame in the shop is never a good idea.
The method I prefer to use for binding sides on all my guitars is laminating. In making furniture I utilized this method often to create just about any desired shape and found it to be very reliable and easily repeatable. This method lends itself to side bending as well as other applications in guitar making, and there are many benefits afforded by using it. If done properly this method will produce lasting results.
Watch a video side laminating demonstration ...
The Benefits of Laminating Guitar Sides
In a set of guitar sides one of the most important characteristics is stiffness. Laminating the sides of your guitar will produce stiffer sides than a solid piece of wood steam bent as described above. Also, steam bending is difficult to repeat accurately. Therefore, if the shape of the guitars sides differs from the ideal (drawing) the amount of volume (cubic inches) inside the box will change as well. Changes in the size of this space from guitar to guitar will have an effect on the resonance of the cavity which may produce inconsistent results acoustically.
By laminating you are in effect removing a heavier wood and replacing it with a lighter wood which will reduce the weight of the instrument. On a classical guitar this is an added benefit. The laminated sides will also be more stable over time and less prone to cracking.
In order to laminate guitar sides a mold is necessary. It will take time to produce an accurate mold. The good news is only one is necessary unless you are in a production environment. The more accurate your mold is the more closely your sides will adhere to the ideal shape of your design. Accurate molds for both the guitar in the book, and in dvd series can be purchased molds by clicking here. Caul drawings are included with the molds.
To clamp the laminations in the mold properly it will be necessary to create a series of cauls to distribute the pressure and create a good seal. I use 4 pieces of masonite the same height as the mold, thinned down to about .090". The outer piece has pieces of wood or MDF glued to its surface to act as clamp pads. These pads should be as high as the caul. Some will have to be shaped in order to match the shape of the caul. The pad surface of some may also have to be angled in order to get proper clamp register. Our molds have pads for 16 clamps. Be sure to place a pad in the middle of the waist. Cauls shown in drawing above.
The Method of Laminating Guitar Sides
Whether it be guitar making or furniture making when laminating wood to create a shape the rule is, more and thinner laminations will produce better results. In order to fit the laminated guitar sides in the heel slots, it is best to make the total thickness of your laminations slightly bigger than the slot. If you are using the side slot cutting sled with a .100" wide table saw blade, it is safe to make the total thickness of the laminations approximately .115". This way it will be necessary to trim the sides slightly to produce a tight fit.
In order to laminate the sides of the guitar, the outer layer of wood (the wood visible from the outside of the guitar) must be thinned down to between .070" and .065". Rosewood at this thickness will bend easily. To make the process go smoothly I typically pre-bend the outer layer of wood. Since the wood is so thin it is not necessary to add water. The bending can be accomplished with heat only. This pre-bending does not have to be very accurate as the laminating process will lock in the final shape, this is done so as not to struggle to get it into the mold. The inner laminations are two pieces of .6mm thick veneer preferably a tone wood. Typically on spruce top instruments we use Alaskan yellow cedar, or even sitka spruce. On a cedar top guitar, pear wood is the preference but I have also used cypress.
First, lightly sand the inside surface of the outer wood especially if it has been pre-bent. Apply the glue evenly, preferably with a roller. Once the surfaces have glue applied sandwich all the pieces together, place them in the mold with the cauls on top, and apply the clamps starting at the waist.
