Gluing Tops and Backs
With two of the side assemblies complete. It is time to focus attention on gluing the tops and backs. I use a 20 inch hand jointer (handplane) to make the joint fit nicely and “‘candle ” the mating pieces, holding them to the light until I can not see light through them. I use 120 self adhesive sand paper stuck to the 20 inch hand plane to fine tune the fit, always working in pairs. I plan to build four instruments this time around and have joined the back and tops for all these instruments. Here is an example of a top and a back pair.
This pair will become a grand concert cutaway with ebony binding and abalone purfling. Below is a picture of all the tops and backs I have recently completed.
The first pair in the picture are the same mahogany, Sitka pair pictured previously. The remaining pairs from left to right are curly maple and Sitka spruce (mandocello), Amazon rosewood and red spruce (grand concert guitar), and another curly maple this time paired with red spruce to make a grand auditorium guitar. The next step is to inlay the abalone rosette.
Thickness Planning Backs, Sides and Tops
I have a number instrument in process. I am building a guitar and a mandocello using Sitka spruce from the Sitka Sonic project as well as closely matching instruments with red spruce.
I use the a Wagner safe-t-plane to reduce the top, back and sides to appropriate thickness. I’m planning red spruce in the picture below.
One of my favorite tools is an antique Stanley No. 80 cabinet scraper that was my grandfather's. It makes quick work of removing tool marks from the safe-t-plane. I often use a belt sander in conjunction with the cabinet scraper.
Once “thicknessed”, scraped and sanded, the sides are dampened and bent using a Fox like bending fixture. Until recently I was bending all the sides, guitar and mandolin alike, with a homemade hot pipe. The Mandolin family sides and binding are still bent on the hot pipe.
Side Assemblies in the Molds
Once the sides are bent, they are placed in an external mold (or cooling frame) and the neck and tail joints are cut and fit together. With these joints fit nicely, the tail and neck block are glued in place. I build my tops with a 30 foot radius top and a 15 foot radius back. The top of the sides are scribed to the 30 foot radius sanding dish, I like to use No 10 block plane to rough the topside profile and when the gap is less than 1/16 inch, the sides (and end blocks) are sanded to the 30 foot dish.
Tops and Backs Cut to Shape
I used a grand auditorium template to mark and cut the tops and backs.
These Sitka spruce tops are from the Sitka Sonic sampling project. These instruments will end up as cutaway bodies. The cutaways will be profiled later.
Here are the backs profiled to the same grand auditorium template.
After the backs are joined together and trimmed to the profile of the instrument, the back graft is glued in place. Here a maple back is shown on the go-bar fixture with the back graft (light color), and the clamping caul (masonite).
Below the back is shown with the go-bar clamps.
After the glue is dry, the graft is shaped. I tape off each side of the back graft for protection and use a block plane and a bull nose plane to rough shape the graft and sanding to final shape.
Next the graft is cut out for the back bracing, and the back braces are glued in the go-bar fixture.
The design of my soundhole rosette is very simple , but I believe it is elegant. The funny thing is that it came about by mistake. A
few years ago I was laying out a very traditional rosette of inner and outer purfling with an abalone middle. Mistakenly, I left out the inner
black white black (BWB). I liked it so much that it is now my standard rosette. Below is the rosette on a completed guitar.
I use 1/16″ BWB purfling and Abalam, a type of abalone product. I have used both straight pieces and curved pieces at different times and I prefer the curved Abalam for time savings. Abalone naturally has discontinuities, therefore, fracturing the Abalam during installation is un-noticable.
The BWB purfling is bent using the hot pipe bending tool shown below. This hot pipe was inspired by some concepts in the Guild of American Luthiers “Lutherie Tools” book and is powered by a 300 watt incandescent light bulb. A 32″ strip will go around the hot pipe 2 and a half times making two complete rings per strip. It takes three strips to make one rosette.
I use the Stewart MacDonald rosette cutter with a Dremel tool to cut the .050″ channels for the rosette.
The inner cut is for the sound hole. For the sound hole, I cut .050 from each side, leaving about .010″ in the center to be cut with a razor knife after bracing is complete.
After cutting all the channels, the bent purfing is weasled into the groove. It takes some coaxing. A strip of nylon is glued between the BWB to displace glue and later it is removed and replaced with Abalone.
Here is the rosette before gluing and sanding.
After gluing and sanding the nylon is peeled out, leaving a channel for the abalone.
The top of the rosette is covered by the finger board on a steel string guitar. Here are the family of four with their shiny new rosettes
Website by Revolution Media