In Part 1 & Part 2 of this Series, we looked closely at the different styles of guitar linings and then examined some of the physics at play within the guitar system in this area of the design. Now its time for the fun part where I get to show you my techniques that I have developed to make my guitars sound better, and to make the process of making these linings as pain free as possible too.
The wood I find to work the best is Spanish Cedar. I used to buy classical guitar neck blanks long enough and then resaw it on the bandsaw. A few years ago I found this huge beam and have been using it ever since. The grain orientation is not super critical, but I do like to have it quartersawn on the face if possible. However flat sawn will work fine too if that is all you have access to.
Spanish Cedar has the right density and weight for my tastes. The guitar remains light, but the linings have enough density to make an effective energy dam and a solid anchor point for the soundboard. It also machines well, and last but certainly not least it smells amazing. Don’t underestimate the power of smell when a client sits down to play your guitar, you want to get all the senses involved in the experience, and some nice Spanish cedar scent wafting out of the soundhole is never a bad thing.
We will be laminating these pieces together for strength and to help them hold their shape permanently. I make it a point to mark them after bandsawing so when I glue them they are in the same orientation as they were in the tree. No reason for this other than it hides the glue seam and looks like one piece when you’re done.
I bandsaw the two pieces out at about 1/8th (.125″) of an inch. then I sand them down on the drum sander to .110″. This gives me a total of .220″ after I laminate these together. I use that number because I find that it is a good thickness for me to bend and work with, and also it’s a multiple of .010″ which is the base measurement for my design. I make all the components to be exact multiples of that master measure to add a deeper sense of harmony in the physical dimensions as well as the tap tuning and other harmonious aspects of the design. You can read more about that in my book “The Art Of Lutherie”
I use aluminum foil to wrap the sides in for bending. I spray them down really well, being sure they are saturated with the distilled water.
Out of habit I mark the top of the wrapping with an arrow pointing to the neck side of the body, I do this with my sides sets to make sure I align them properly and keep the right side facing up.
Next into the side bender. The super old version from back in the 1990’s with the light bulb base remnants inside. I am using two heating blankets that I had custom made many years ago, one on top of the wood and one on bottom of the wood. Having a heat source on each side is really helpful. If you had to, you could bend each piece individually and it would work fine, but stacking them together as I do is better if you have sufficient heating to get them both up to the right temperature for proper bending.
The new side benders and heating blankets you can buy these days are far superior to what I am using, so no need to try to replicate what I have here.
After I take out the linings, here is what they look like.
This next part is very important!
Do you see the white strip of material in the mold? It’s a sheet of High-Density Polyethylene. I bought a sheet of this a long time ago as my friend Jim Olson told me it was how he made his own filler strips for installing abalone in bindings. I never ended up using it for that, but I found many other great uses like this. It’s 3/32″ thick. (I bought it from US Plastics)
Using the HDPE (or something similar) is critical for two reasons
- It keeps you from gluing the linings to the mold, pretty obvious…
- It simulates the thickness of the guitar side and helps to laminate the linings in the exact set of curves they need so that when you glue them in place they will not be putting any tension on the sides at all.
The best sounding glue of all that I tested for this application was Gorilla Glue. It has many features that make it great for this such as; no thermoplastic creeping (like Tightbond), Works better when moisture is in the joint (this makes it so I can glue it right away even if it’s not totally dry after the bending process), squeeze out is easy to clean up and sand, one part application (not two-part like epoxy).
I use an old credit card to spread out a thin layer of glue on one side of the joint. I don’t want to do too much because I don’t want too much squeeze out.
Then into the mold with the white HDPE in place and applying clamping pressure.
For clamping cauls, I use some pieces of Cedar closet lining/flooring (tongue & groove) cut up to about 3/8 X 5″ in length.(you can use anything for this, I just had some of that stuff left over from building some furniture for my wife and found this great use for it) They are around 1/4″ thick and they have some Scotch tape on one side to prevent it from being glued to the linings. They also help to spread out clamping pressure more evenly.
I start by clamping all around the periphery on one side first.
Then I stand up the mold and clamp from the other side too, positioning the clamps to get even pressure across my clamping cauls.
Denatured alcohol is great for cleaning off the workbench and whatever else gets glue smeared on it.
Here is the crazy looking final product which I leave overnight to dry.
The next morning I take it out of the mold
Clean and square up the sides on the belt sander.
Check to make sure things are in proper alignment.
Lightly sand off any glue that seeped through the wood pores or squeeze-out from the glue joints.
Then I make sure I have enough material to get 4 pieces from this laminate. I rough cut my linings to about 18mm. this ends up being .7″ by the time I am done installing them on the guitar which again is a multiple of my master dimension. Don’t forget to account for the width of the saw cut. The linings don’t have to be as tall as mine, I just like them kind of beefy.
[warning_box]Be careful with this part and all parts of this tutorial! Do it at your own risk. This process is dangerous and should not be done unless you have experience with a bandsaw and woodworking tools in general. Keep your fingers away from the blade, let the wood get ruined if necessary, you can always make another, but you need your fingers![/warning_box]
I set the bandsaw with a 1/4″ medium tooth blade and adjust the fence for my cut.
I work the linings through, so that they stay tight on the fence and slowly work my way around making the cuts.
Next I mark the bottom (the part that the top or back plates will glue to) pieces so I am sure I have one for each side of the guitar.
Next I go to the pin router to round over one edge of the lining strips with a 3/16″ round over bit that has a bearing guide on it. You can do this in a safer way with a router table, but I don’t have one anymore so I use the pin router which works well for me.
The little spring clamp is there to temporarily hold the piece and keep me from getting my fingers too close to the bit. Once I move it along some, I remove the clamp and continue around the piece until it’s done. I leave the first portion of the lining square so I am not pushing the end of the piece into the spinning bit as it would be catastrophic and I can always plane or sand that extra bit of roundness into the piece at that point later if needed.
After I’m done with the round-over bit, I do a little clean up on the slight ridge left by the router bit. You might not have this if you use a router table instead of a pin router.
This guitar is a cutaway so I made a straight piece too, and I’ll show you how I approach it as well in a moment.
After a couple of seconds of clean up with a plane and sanding block, my linings are ready.
I use a more heavy duty clamp to hold these in place because I am gluing with a thixotropic epoxy and I need the strong force to squeeze it out properly. I do take great care though to be sure that I am not putting too much pressure on the side and leaving a mark or forcing it to flex in a way that could cause a fracture.
Note – I don’t have a photo of this but I put a strip of masking tape along the inside edge of the lining glue joint to catch squeeze out. Then after I install the clamps I just pull off the tape and the squeeze out along with it for very clean and nice looking linings. I also seal the linings (not on the glue joint part though, just the parts that will be seen inside the guitar) with shellac before gluing to keep them free of glue marks too.
To move the piece up and down with the dome shape of the guitar sides, I simply make some cuts nearly all the way through the lining to allow it to bend. To move the lining up, I make a cut in the top and then flex it upward closing the cut. When I apply glue I work it into the cuts a little and then as I clamp it and flex it, the cuts are glued together and become as strong as if there were no cuts at all. If you look closely at the photo above you will see the micro saw cuts in the waist and upper bout areas that I made to flex the linings into the right shape.
Note – Remember to never force the lining in a way that puts pressure on the sides, over time that could lead to problems. I want the linings to be strong and solid, but at rest having a peaceful stress-free glue joint with the sides.
Now for the cutaway.
I first put tape on the straight piece that was already rounded over with the other lining strips.
trim the excess tape
Next I clamp a piece of wood to the bandsaw and use it as a depth gauge so I can eyeball my kerfing cuts (I have a pen mark on the piece of wood for approximate reference to kerf size) and carefully push the piece into the blade and then pull it back out making my kerfed lining. I like to leave about .015″ of wood after the cut.
I make just enough for the cutaway areas on the top and back sections.
I make the cuts closer together on the tight part of the cutaway curve and then pre-bend each kerf cut to help it get the shape to fit perfectly without breaking.
Now it’s a perfect fit to the shape of the mold. I can get away with using kerfed lining in the cutaway because when I glue the lining on, I use a thixotropic epoxy and I smear it into the cuts so that when it is glued in place it is essentially a solid lining again due to the thick epoxy filling the cuts. The epoxy cuts better with a router when I cut the binding channels and does not gum up like Tightbond. After gluing it’s like a solid lining in the cutaway, but one that is applying no tension to the sides and is a flawless fit while still retaining all the same strength.
After I’m done the sides are so strong I can take them out of the mold permanently. One thing to note also is that you should make the ends of the linings fit tightly to your tail block. I start from the tailblock and fit the piece to the shape to make sure there is no stress and then trim each end until I get a good fit. Also be sure to put some glue on the ends also so the linings can be affixed to the tail-block as well.