Depending of the material used for your head piece and the shapes that are incorporated into the head piece design, there may be a need to pre-bend wood bindings to minimize cracking. The headpiece design that I have used for years minimizes the need for pre-bending as it consists of sharp corners without curved transitions, as shown in the accompanying photos.
Preparing the Binding:
Although many Acoustic Guitars do not have headpiece bindings of any sort, there are quite a few that do. If you have a bound fingerboard for example, you will probably want to bind the headpiece in a similar manner.
The first decision is the type of binding that you will use. If you are going to bind the body of the guitar with a wood binding, you will more than likely be consistent and carry that design through onto the fingerboard and headstock binding.
If, on the other hand, you will be using a plastic binding, you will most likely use that design throughout the instrument.
Wood Binding Preparation:
Depending on your headpiece design, you may be able to skip this step. If your design includes a radius edge at the top of the headpiece, you will want to prebend the wood purfling and binding materials.
Prepare you Binding Materials. Purfling can be almost anything you want, but for this example, we will use a single strip of light colored wood. This can be either maple or holly veneer. The Binding looks the nicest, (my personal preference) if you match the wood of the guitar binding, and this is usually the same wood as the back and side plates.
Make the strips about 1/8″ high. Bindings should be about 1/16″ wide. I prefer to prebend the binding/purfling combination by using a hot pipe or the barrel of a soldering iron. You should pick a pipe or iron very close to the same diameter as your radius on the headpiece.
Bend the Purfling First:
You only need to do this if you have tight bends as part of your headpiece shape. the transition between the nut and the wide part of the headpiece is often a questionable area if pre-bending is necessary. If the binding is thick enough, it will crack when attempting to make this curve. I usually pre-bend my binding in this area.
To Pre-bend, take a strip of purfling material, cut to the proper length to go around the entire perimeter of the headpiece plus a little bit. I usually cut these pieces about 2″ long and finally cut them to within about 1/16″ long on each side of the nut. Carefully mark the centerline of each curve on the face of the strip.
Heat up your pipe or soldering iron barrel. If you choose the pipe method, cut a section of copper piping to length and heat with a propane torch.
Dip the purfling in water and apply the area to be bent to the pipe. Use a slow rocking action to generate steam. When the wood dries, dip the strip in the water again and repeat until you have the curvature formed. Repeat for the opposite curvature. Double check the curve locations by holding the purfling against the Binding Jig.
Bend the Binding:
Utilize the same method for bending the binding as you used for the purfling in the above example. You will need to exercise more care with the bending process of this wood as it is thicker and typically more brittle. As you bend, be alert for any wood fibers cracking or poping and ease up if you hear this. Repeatedly use the water bath until you have the curvature just right.
GLS Tip #1: Prepare several strips of binding materials, as you may break several strips before finishing up the bending operation. Take it slow and easy. Make sure you heat the strip up on the iron prior to applying any pressure. If you consistently break strips, your wood may not have a strong enough fiber to allow adequate bending, or you may be trying to bend a strip that is too thick.
If your strip is too thick, consider bending 2 pieces of binding of 50% of the thickness and laminating them during the gluing process. This procedure works really well at more gentle curvatures without the need of heating or pre-bending.
GLS Tip #2: Make your purfling and binding strips slightly higher than the channel they will be glued to. About .5mm to 1.0mm works good. This will allow you to scrape the top down flush with the headpiece laminate.