Pore Filling With Epoxy

After installing purflings and bindings, it's very rewarding to scrape them level, carefully round over the edges, then sand the top, back and sides in readiness for the first steps in the finishing process. It feels like the end of a journey while at the same time signifying the beginning of another equally challenging one.

With final sanding on this guitar complete, I've taken the first steps towards pore-filling the back and sides with epoxy, a process that finally reveals the true beauty of the wood. As a hobby builder, many months have inevitably elapsed before I get to this stage, but the rewards make the effort and the wait worthwhile. Along with stringing a completed guitar up for the first time, seeing the figure and colour of the wood magically appear as the first coat of epoxy is applied is surely one of the highlights of the building process.

On a cautionary note, a problem with some epoxies is that of amine blush, a waxy residue that forms as the epoxy cures that can interfere with adhesion and curing of subsequent top coats. From what I've read on the topic, spending a little more on a good quality epoxy is worth considering as they're less likely to be susceptible to blushing. Whichever product you choose, once the epoxy has fully cured a thorough rub down with a damp cloth - or, better still, one dampened with a 50/50 mixture of water and denatured alcohol - is a simple precaution that eliminates potential problems. There's wisdom too in avoiding the application of epoxy when the ambient temperature is falling and relative humidity is therefore likely to be rising - conditions said to exacerbate blushing.

Hats off to Todd Stock for putting together these very informative tutorials:
Epoxy Pore Filling Part 1: Application of First Coat & Sealing a Rosette
Epoxy Pore Filling Part 2: Prep & Application of Second Coat
Epoxy Pore Filling Part 3: Prep & Application of Third Coat and Prep for Finishing

Cheers
Pete

The Secret's Out!

A friend contacted me yesterday seeking advice about a suitable guitar upgrade for her daughter. As I've secretly had plans all along to make a gift to her of one of the guitars I currently have under construction, it seemed like a good time to reveal my intentions. As a result, I've decided to prioritise the completion of this guitar with a view to presenting it to her as soon as I can.

As luck would have it, I finalised the construction stage only a week ago - the task of finishing therefore begins in earnest. The first step is to fill the pores with epoxy after which two coats of Ilva TF23 sealer will be applied immediately prior to the first of the KTM-SV top coats.

I'll document the process here for the recipient's benefit and in the hope that it's of some interest to others as well.

Cheers

Pete

Guitar Necks: A Recent Improvement

I had time to daydream about guitar building over the last few months even if I didn't have opportunities to make progress in any practical sense. Among other things, my ruminations concerned construction of the neck in terms of how I might improve the design and produce more consistent results. Finally, with the university year over, I'm in a position to turn those thoughts into actions. 

In keeping with my usual method, two knock-down bolts extend through the headblock into threaded plugs embedded in the neck tenon. Although this is a popular and proven design, I've come to realise that there's an inherent weakness: if the bolts are overtightened through the soundhole by an inquisitive or over-zealous owner for some unknown reason, there's a chance that the force they exert on the plugs could eventually split the neck at the extremity of the tenon. However remote this possibility might be, it seems prudent to provide some reinforcement. With that in mind, I've modified my routing jig so that the tenon it produces is narrower than it once was, the idea being that I can build it back up to the desired width of 20mm by gluing a 2mm layer of wood to either side of the tenon as shown in the picture below. Crucially, the grain direction of these outer layers is at right angles to that of the neck shaft which provides good protection against splitting.

I'd like to achnowledge the luthier who came up with this idea; if I could only remember who they are I'd certainly do so!

I'll report on further improvements to my neck construction methods in an upcoming post.

Cheers
Pete

What's on the Bench?

Having swapped plane and chisel for scalpel and scissors, here's a picture of a recent project!

A Cane Toad gives his life for science.

I may have left it a little late in life to go "back to school", but the move has at least provided me with a new and exciting challenge as well as a much-needed sense of direction. Having said that, I'm already looking forward to a break at the end of the year and the opportunity to resume my regular woodworking pursuits.

I'll be back!

Cheers
Pete

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.

Cheers
Pete

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.

Cheers
Pete

Soundports

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.



Cheers
Pete