Sunday, June 24, 2012

Preparing Bindings and Purflings

When it came to preparing purflings for two of the guitars I'm currently building, the first step was to laminate veneer sheets into a black/white/mahogany/white/black sandwich. Rather than the black-dyed maple I used as the outer veneers when preparing an earlier batch of strips, I substituted black fibre sheet (sometimes called fish paper) this time to minimise the risk of deformation or splitting when the strips are bent to fit the purfling channels; the last time around, some of the black maple veneers collapsed slightly in the area of the waist and had to be discarded.

The brayer pictured above is a tool commonly used by printmakers - I sourced mine from a local art supplies store. It's the ideal tool to quickly and evenly spread glue when laying up the veneer sandwich. Titebond III is a glue well suited to this task; it's relatively heat and moisture resistant and the layers of veneer are less inclined to de-laminate when the strips are moistened and bent to shape.

With a small circular saw mounted under my table-saw bench and equipped with one of Stewart-MacDonald's fret slotting blades, I switched the saw on and raised it slowly, cutting through a masonite sheet I'd clamped over the table until the blade was fractionally higher than the thickness of the veneer sandwich, at which point I locked the saw's adjusting lever. Feeding the veneer sandwich through this very fine blade minimised wastage and resulted in an extremely clean cut. I was quickly able to produce enough purfling strips for two guitars, with a couple of strips left over as spares in case of breakage or buckling.

Preparing purflings for the rosewood guitar was an even simpler exercise; they're a simple combination of one black and one red veneer strip - thin enough that strips could be cut from the veneer sheet using a steel rule and a craft knife and pliable enough that pre-bending the strips is unnecessary.

Where the bindings are concerned, I chose to glue contrasting veneers to the edges of the binding strips - again using Titebond III - prior to bending them. Ebony bindings can be a pain to bend so I took the precaution of spraying them lightly with SuperSoft 2 veneer softener the day before I bent them - the softener plasticises the wood strips somewhat, reducing the chance of breakage. Taking care to arrange them into matched pairs, I taped the strips together, misted them with distilled water then wrapped the assembly of strips in brown paper and aluminium foil and bent them in my Fox bender. I began cranking down the press screw at the waist when the thermometer reached 240F and, when I'd bent the upper and lower bouts and applied full tension at the waist, let the heating blanket climb to 310F where I let it sit for a further 5 minutes. I switched the blanket off and removed the binding strips when the machine had cooled to room temperature.

Despite the fact that I'm currently working full time and distracted by those unpleasant but unavoidable weekend chores, I'm setting myself modest targets every week and making steady progress. Installing these purflings and bindings on the three guitar bodies is my next task.


Thursday, June 7, 2012

Guitar-Shaped Objects

With these guitar bodies assembled at last, I'm better able to imagine what the completed instruments might look like. It's very satisfying to have reached this stage, but I know there's a lot of work remaining.

Sitka Spruce/Claro Walnut; Sitka Spruce/East Indian Rosewood; Redwood/Claro Walnut

Having laminated the veneers from which I'll slice the purflings, my next job is to prepare purfling and binding strips, then rout out the ledges on the bodies to accommodate them. With the right jigs and tools this shouldn't be a particularly challenging job, but as a "hobby builder", the interval between guitars is significant; I'm not usually able to perform this task frequently enough that I ever feel entirely at ease with the process. With three instruments in the pipeline though, I should be feeling more confident by the time I carry out this step on the last of the current crop.


Monday, June 4, 2012


I've posted Matt Mustapick's observations on soundports before, but it seems an opportune time to do so again:

"This concept came originally from the great classical maker Robert Ruck, who puts two small holes on each side of the guitar, very close to where the neck joins the body, rather than one larger hole. The main advantage of the soundport is that it gives the player a "front row seat" to enjoy a strong direct signal from the soundbox. This feature takes nothing away from the forward projection of the instrument. From 20 feet away the guitar is just as loud. For anyone closer to the guitar, it adds a great deal of richness to the sound, owing to the dual sound source which creates a stereo field."

Prior to marking and cutting the side soundports, I took the precaution of gluing two thin layers of veneer to the inner surface of the sides as reinforcement.

Cross-grain veneers provide a measure of protection against cracks

In recognition of the veneers' primary purpose which is to strengthen the area around the ports, their grain runs perpendicular to that of the sides. Some builders argue that cross-grain veneers actually promote cracking by restricting the expansion and contraction of the sides that would otherwise occur. While I accept that such veneers do indeed limit the capacity of the sides to move with fluctuations in humidity, the distance between the linings in this area of the upper bout is small and any potential dimensional change is minimal. If it was a credible risk, we'd surely see cracks developing where the headblock and tailblock similarly restrict the sides' movement across the grain.

In addition to their practical role of protecting against cracks, the veneers also provide me with an opportunity to introduce a contrasting maple line around the walnut guitar's port and extend the rosewood guitar's black and red theme.

Dremel extension handpiece with mini circular saw blade fitted - before and after

A mini sanding drum in the Dremel handpiece takes me to the line

Final sanding required, but essentially, they're done

Very soon, I'll prepare myself mentally for the onerous job of installing purflings and bindings - a task that never seems to get any easier or less stressful!

A recent guitar, with soundport

Useful links:
The Shrinkulator is an online tool that calculates dimensional change in wood with variations in moisture content or relative humidity.