A free-floating top is somewhat of a misnomer. As the name implies, the top is not free to float, but it IS glued to the sides without any clamping pressure, which is the ideal method to eliminate any stress in the most important sound-producing element of the entire instrument building process.
This process can be used for most any acoustic instrument and is a great method to improve sound from your instrument. Mass produced or factory produced instrument will never use this method as it is too time consuming, but you will find in producing your own handmade instruments this can be a very efficient process, once you have the setup complete.
Japanese Pull Saws
Wood Chisels
Sandpaper 180, 120 Grit
Titebond Glue
Wood Lining Blocks
Small Hand Built Miter Box
Wet Cloth
Whether it is a Classical Guitar top or an Acoustic Guitar top or a Ukulele, the free-floating top, as I call it, can add some tonal qualities to you guitar - arguably so that is. In this article I will only address the installation of the free-floating acoustic guitar top. Installation for classical guitars and ukuleles are so similar, this post will give you all the information you need for every acoustic instrument.
Since the guitar top in the most important sound producing element of a guitar, it stands to reason that reducing stress related to this element will improve the overall sound of the instrument.
I feel that reducing stress throughout the instrument building process is very important and when I build my instruments, I ensure that everything fits together perfectly before gluing.
Not only does this give me a great sounding instrument, it improves the stability and the durability of the instrument.
By reducing overall stress to important joints, like the top plate and back plate attachment joints, side joints at the neck and tail blocks and all of the bracing, you are removing all but the string tension on the instrument - which is a necessary stress on the guitar.
Check to see that the joint between the top and the sides is tight and all of the bracing is set perfectly in place. Also double check that the center-lines of both the top and the sides line up perfectly. If you need to do some last minute adjustment, you should do it now.
Before you start your gluing operation, clean the side where the lining block will be attached thoroughly with Acetone if the guitar sides are built from exotic wood or has heavy resins. Make sure no color comes off on the cloth for we are going to use Titebond to glue to top.
First place the top face down into the inside form. Be sure to check for any foreign objects in the form prior to doing this. Also the top has to be cut to the shape of the inside form to fit properly.
Place the sides into the inside form with the side to be glued to the top down and put Spreader jacks into place to secure the sides tightly to the form.
Get the lining block materials ready, glue and some clean up tools, like a small chisel and a wet cloth. Also place a little pool of Titebond on some wax paper and have a small veneer spreading stick ready to coat each block. If the sides of exotic wood are cleaned adequately with acetone, the blocks can be safely glued to the sides with wood glue. Otherwise epoxy will be needed. Epoxy should be the slow setting type to give you plenty of time to set the blocks around the entire perimeter of the top plate.
Put a lining strip in the Miter Box and make the first cut. At most each block should be no longer that about 1/2" to 5/8" (12-15mm). You can choose to make shorter blocks around the sharp bends or shape them slightly with a sanding stick dowel or a belt sander.
Spread a small about of glue on the back and top of the block with the small veneer spreader and make sure all excess glue is cleaned from the block and set it into place. Move it back and forth slightly to get the block to "set". Move on to the next block. I like to have a small shim available to stick between the pieces to ensure that the spaces between the blocks are exact. You will find that the Titebond will set-up quite quickly, especially on the Spruce or Cedar tops. If there is any glue squeeze-out clean it up immediately with a wet cloth. Also for easiest Titebond cleanup wait until the glue is semi-setup and can easily be removed with a sharp chisel.
For now just butt up to the top braces as you can decide on whether to place brace extensions on the top of the braces or not. Another common Acoustic Guitar method and Classical Guitar method is to set one of the lining blocks on top of the brace scallop and glue it to the brace and the sides. This is a case of personal preference, but it has been used on many classical guitars, including the famous Hermann Hauser Guitars.
Tip: After you progress every 6 blocks or so - go back and check that the blocks are still seated properly and have not pulled away from the sides. If you have a stubborn block you may need to put slight pressure on it with a Wooden Cam Clamp and a caul (usually made from a small piece of lining that is reversed to hold the lining against the side).
You can do this as you go too, but just make sure you clean up any glue smears with the wet cloth that you can see. After the glue is dried, lightly sand the lining to make is smooth and even. You will be knocking off some of the edges by doing this and creating a much smoother appearance.
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