Lessons in Finishing

Having completed only a handful of instruments with sprayed finishes, it's not terribly difficult to identify flaws and aspects of the process I've yet to come to terms with. Having said that, it helps to keep things in perspective and remind myself occasionally that the perfect finish - if there is such a thing - is an impossible dream for us mere mortals, a fact apparently acknowledged by many U.S.-based builders who happily farm out the finishing of their instruments to a professional. I'm sure the health and safety aspects of working with solvent-based materials play a significant part in that decision too. Down here at the bottom of the world, however, I'm left with the task of identifying problems with my technique, improving my finishing processes, finding materials that suit my situation and hobbyist status and developing the most effective means to combine and apply them. Although it's been a laborious and sometimes frustrating process, I'm cautiously optimistic about my next guitar - but then I always am!

I've made some mental notes of late where finishing is concerned:

• Do a thorough job when pore-filling. At this point in time I'm using epoxy, as do many others. Aside from its effectiveness in filling the pores, I like the way it enhances the figure and colour of the wood it's applied to. Briefly described, pore-filling consists of applying the epoxy to the wood with an old credit card or spatula, then removing as much as possible from the wood's surface, leaving epoxy only in the pores. It often takes several sessions, allowing the epoxy to cure and sanding off dust nibs and ridges before the next application, before all visible pores are filled, but it's worth the extra effort given all the hard work that's preceded it.
• Wipe down cured epoxy thoroughly. A by-product produced as epoxy cures is something called "amine blush", a waxy residue that can have an adverse effect on subsequent coatings. Thankfully, a good rub down with a damp cloth, or one dampened with a mix of denatured alcohol and water is sufficient to remove it. From what I've read, it's worth spending a little extra on a good quality epoxy and applying it in a warm, low-humidity environment to reduce the impact of blushing. The manufacturer of the boat-building epoxy I use contends that their product is not prone to amine blush, but I tend to give it a precautionary wipe down anyway as added insurance.
• Find a compatible sealer. Oily species such as rosewood can be particularly problematic and can adversely affect or even prevent curing of top coats. It's worth experimenting with sealers or barrier coats to find one compatible with epoxy and your chosen top coat material. While some builders sand the epoxy pore fill back to the wood, in which case an effective sealer becomes particularly vital when using any of the oily wood species, I choose to leave a thin layer of epoxy on the wood - excluding the soundboard. The epoxy serves to lock in any oils present in the substrate and the task remaining for me has been to find a effective product to act as a tie-coat between the epoxy and the top coats of KTM-SV. Adhesion of my top coats has been a recent concern, but hopefully I've identified a compatible set of finishing products as I described in an earlier post.
• Find a suitable top-coat. Having set myself the long-term goal of selling my instruments, I've pondered the various features that a prospective purchaser might commonly be looking for. A durable, high-gloss finish is one them, and is one aspect of instrument building that continues to test me, particularly as I've vowed to avoid solvent-based materials such as the much-used but far more hazardous nitrocellulose lacquer.
• Drop-fill early. Any small gaps in the bindings are evident once the first top coats are applied. It's worthwhile dealing with gaps and pin holes while there are plenty of remaining top coats to even out these repairs, the caution being that with only a couple of coats of finish in place, extra care needs to be taken so as not to sand through to the wood when levelling.
• Level sand with the finest grade of abrasive paper which will get the job done, i.e., top-coats are necessarily thin and remnant scratches from coarser grades of paper are difficult to fill. With practice, sprayed finishes shouldn't need much in the way of leveling and, as I've become more comfortable with the settings on my spray gun, I've not found it necessary to level sand with anything coarser than 600-grit.
• Final level sanding of the cured top coats can't be rushed, i.e., don't be in too much of a hurry to crank up the buffer! Patience and a generous helping of elbow grease are pre-requisites as the instrument is wet-sanded in readiness for final buffing.
• Be careful when sanding the edges of the guitar, and especially so around the headstock, where it's easy to "roll-over" an edge with the sanding block and remove more finish than is necessary or, heaven forbid, sand through to the wood. I haven't sanded through yet, but I'm keenly aware of the potential to do so.

Cheers

Pete

Continuous Improvement - a Hard Road

I tend to be hyper-critical of my own work, so it's gratifying to be able to identify at least some aspects of my instruments which I have difficulty finding fault with. Perhaps after 20 years of trying I've simply had enough practice, or perhaps as I've slowly accumulated a decent collection of tools and equipment, developed a range of useful jigs and constantly reassessed and refined my processes, a satisfactory outcome is now more likely.

Now that I've finished congratulating myself, I might add that there's plenty of scope for improvement in several important areas including fretting, setup and finishing. Even more significantly, having any real control over the tone of the finished instrument - except in the broadest sense - seems the most formidable challenge and is one reason I'd be reluctant to take on commissioned work should I ever decide I'm ready to sell my instruments.

An important part of the process of continuous improvement is an dispassionate self-appraisal of my work, involving a comparison of actual results with the work of others and the benchmarks I've set for myself. If my own personal vision of perfection is a valid goal - as it almost certainly should be - it helps to be mindful of the old conundrum involving travel: if we manage only to halve the remainder of the journey each day, we'll approach but never quite reach our target destination. It's a useful metaphor to reflect on when striving towards mastery of any skill; the parallel where my guitar building efforts are concerned is that rapid progress seemed far easier to achieve as I began this adventure, but as time has passed, improvements in the quality of my work seem less significant and more infrequent and difficult to achieve. I do wonder at times whether it's the challenges I constantly confront that form an important part of lutherie's appeal.

While I'm certainly in a position to cast a critical eye over the standard of my own workmanship with a reasonable degree of objectivity, my own limited playing skills will stand in the way of any useful self-critique where tone and playability are concerned. Bearing in mind that it's the views of the guitarists I build for that should be of primary concern, I really do need to seek constructive criticism from skilled players if I'm to make progress with those all-important aspects of the craft. Soon, perhaps, I'll hunt down a willing local participant with that goal in mind.

Cheers

Pete

Grafted Coatings' KTM-SV - A Sticky Problem

With two guitar necks and a body almost ready for finishing, it's an ideal opportunity to refine my spray finishing techniques as well as experiment with a new seal coat material.

As I've reported previously, I'm pretty happy with Grafted Coatings' KTM-SV, the finish material I've used on my last two guitars, however, as I removed the finish in readiness for gluing the bridge in place on both guitars, I was a little concerned by the poor adhesion of the top-coats to the shellac beneath it. Shellac is well known as a material that readily sticks to almost anything, however, it seems the same can't always be said for the adhesive properties of other coatings when applied to shellac. Most notably perhaps, shellac adheres well to epoxy, but epoxy cannot be used on top of shellac. Go figure.

A recent thread on the Official Luthier's Forum discussed this issue and attracted some interesting responses. It's comforting in a way to read that others have had similar experiences and are also looking for solutions. It's also pleasing to see that Grafted Coatings themselves are taking a keen interest and have volunteered to prepare some test panels with a view to recommending a suitable sealer for their KTM-SV product.

I'm looking forward to Grafted Coatings presenting their findings, but in the meantime, I'm keen to try a two-pack polyurethane barrier coat manufactured by Ilva which luthier Randy Muth uses and recommends. I'm pleasantly surprised to have discovered a local source for Ilva products and relieved that the distributor - who commonly deals in commercial quantities - could be persuaded to decant a couple of litres each of the resin, hardener and thinners for me.

If I have any qualms, it's that I'll be reverting to use of a solvent-based product when it was the safe, environmentally-friendly aspects of KTM-SV that attracted my attention in the first place. Thankfully, use of this product is likely to be limited to two light coats, and with the usual precautions of good ventilation and a twin-filter respirator with vapor cartridges, I'm prepared to give it a trial run.

Cheers

Pete

Buy Now!

It's been a long time coming, but with the Australian dollar at last reaching parity with the U.S. dollar (and predicted to climb even further), the parcel delivery van has been an increasingly frequent visitor of late. With such a strong local currency at present, Australian exporters are feeling the pain, but as an importer of "must have" guitar-building tools and exotic woods, I'm in my glory.

For too long, as my finger hovered uncertainly over the "Buy Now" button on the Allied Lutherie or Luthier's Mercantile web sites, I was forced to add up to 50% to the advertised U.S. price as I made a rough conversion to my own currency - and that's before I'd factored in those truly horrendous international freight charges. Often, I'd indulge in a little harmless fantasy and fill my online shopping cart and then, after a moment or two to savour the experience, grudgingly click the "Empty Cart" button after reality had kicked in and I'd calculated the final cost!

East Indian Rosewood

I've never been one to horde wood, preferring instead to order materials to satisfy immediate needs, but after my recent purchases I must admit it's nice for a change to be able to pick and choose from the growing collection of soundboards and back and side woods awaiting my attention. I can see why wood acquisition can become an addiction for many builders!

Cheers

Pete

Routing the Saddle Slot

None of my jigs are particularly attractive, polished or professional, but they're certainly functional and take the guesswork and inconsistency out of many tasks.

Routing a slot in the bridge blank into which the bone saddle will be fitted is one job I've given over to the ugly but effective jig pictured below.

The Macassar ebony bridge blank is affixed to the base of the jig using double-sided tape (what would I do without it?); the blank's positioning isn't really critical. The blank is bedded down with a few taps from a soft-faced hammer which more than adequately secures it for the duration of the process - the tape is tenacious stuff!

As you can see, two adjustable guides sit atop the jig and, with the plunge router riding snugly between them and the router bit sitting just proud of the wood surface, are adjusted so that the bit will accurately track the line of the saddle marked on the bridge blank.

I rout the slot in several passes, each one a little deeper than the last, until I hit the depth stop set on the router body.

I'm tempted to add sliding stops to either end of the jig to limit the router's travel, but for now, a couple of strategically positioned panel pins serve this purpose well enough, which perhaps explains why I haven't been in any great hurry to make that modification - I'd rather be building guitars than building jigs.

I'll show the next stage of the process in a future post.

Cheers

Pete

Eye Strain Reduced!

For making marks on dark woods such as rosewood and ebony, I use these white ballpoint pens which I discovered at an art supplies store. They're a vast improvement over the graphite pencils I made do with for so long.

Cheers

Pete

The Flat-Top Guitar That Isn't

With some exceptions, steel-string acoustic guitars - often referred to as "flat-top" guitars - actually have arched or domed backs and soundboards, the advantage of which is arguably more structural than tonal. There are those who would argue that where soundboards are concerned there's little benefit in introducing an arch, but I think it's widely accepted that a domed top is better able to flex with variations in humidity thereby reducing the chance of cracks developing over time.

The mating surfaces of the various braces attached to the back and soundboard are curved in such a way that the dome is maintained in the finished instrument. Typically, the top assumes the shape of a section of a sphere having a 25 foot radius, while a 15 foot radius is commonly used for backs.

The following sequence of photos shows the method I use to shape the braces:

After the brace stock has been thicknessed to 7mm, I pencil the radius onto the brace blank using the appropriate acrylic template. In this case, I'm shaping the braces for the guitar back.

A 12-inch disk sander makes short work of the excess wood outside of the pencil line and it's surprising just how accurately the curve can be defined at this stage. A shop vacuum hooked up to the sander takes care of the wood dust pretty effectively.

With very little additional effort, the final arching of the brace can be established. Here, I'm using a hollow form whose radius matches that of the finished brace. Using 180-grit and 240-grit sandpaper in turn, the radius is accurately sanded into the brace. The scrap of wood held in place by my right hand helps prevent the brace from rocking sideways as it's sanded.

The finished back braces, ready for gluing.

Cheers

Pete