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

Joining the Back and Top Plates

Preparing the back and soundboard halves for gluing is a relatively easy but critical step in guitar construction. Many luthiers use a traditional shooting board similar to the one pictured below. The back or soundboard halves are placed flat, one on top of the other, with the edges to be joined overhanging the ledge slightly; the plane is pushed along the length of the overhanging plate edges.

My own take on this has been to build a shooting board in such a way that the plates to be joined are held vertically between two cork-lined jaws as the picture below shows. The top or back plates are clamped lightly and accurately aligned before the jaws are fully tightened. Truing the edges then takes place with the plane guided by the vertical fence, with pressure applied from above and the plane held in the familiar and more controllable upright position. The advantage of this configuration for me is that, once they're firmly clamped, the plates are immobilised and I feel I'm able to apply more even pressure than a more typical shooting board would permit. To ensure an accurate cut, my trusty old wooden plane has been fed through the drum sander to true up the side which bears against the fence.

A few judicious strokes with a sharp plane blade are generally all that's required to achieve the perfect joint, after which, the halves are glued together using the jig shown below. As you can see, wedges are tapped into place to apply the necessary clamping pressure. The underside of the blocks is faced with 80-grit sandpaper which reduces slippage once the wing nuts are tightened and the wedges are tapped home.

Cheers

Pete

Some Final Observations on KTM-SV

I realise I've banged on about Grafted Coatings' KTM-SV water-based finish a bit over recent months but, as a final word on the subject, it's probably worth reviewing what I've read or found out for myself for the benefit of others who find themselves facing the same challenges I did with the finishing process.

From memory, I was alerted to this finish by Rolfe Gerhard’s article “KTM-SV – An Overlooked Finish”. The way Rolfe described it, Grafted Coatings’ KTM-SV sounded like the safe, environmentally-friendly finish material I’d been vainly searching for to that point, possessing most of the positive attributes of the other commonly used water-based products, with some important differences. Grafted Coatings’ web site describes it as “a waterborne, oil-modified, self-crosslinking urethane”, which immediately separates it from the better known waterborne acrylics.

On the plus side, it’s reportedly harder than the likes of Target Coatings’ EM6000 or Grafted Coatings’ other instrument finish, KTM9, although how that’s been determined with certainty I’m not quite sure. Also, not having an acrylic base as they do, it doesn’t display any of the blue cast some report with those products. For me, however, the most telling statement in Rolfe’s article is that he’s had instruments in the hands of players for two or three years and no problems have arisen in that time. For my own peace of mind I wish it were longer, but I’m comforted by that information nevertheless. For me, this is the acid test in terms of any new or newly adopted product’s suitability as an instrument finish. How many stories are there of instruments finished with KTM9 developing bubbling or sticky necks over time for instance? KTM9 still has its fans, but I think it’s fair to say the enthusiasm for that particular product has diminished over the past few years, due in part perhaps since prominent advocates such as Mike Doolin and Charles Fox have reportedly jumped ship and turned to polyester and nitro respectively. The disappointments with U-Beaut’s original Hard Shellac are well documented and, although it’s been reformulated, I’m still unconvinced of its suitability given my recent experience with it as a sprayed finish – French polishers (and Australian ones for that matter!) may have more luck. In any case, I don’t think it’s proven itself over a long enough period to be considered seriously, particularly if you’re as cautious as I am and share my view that warranty work is bad advertising, even if it’s expertly carried out.

Because I avoid mineral spirits (turpentine) whenever possible, another plus for me is that unlike other waterborne products, KTM-SV can apparently be wet-sanded using water as the lubricant. In his article, Rolfe says that witness lines buff out invisibly, which I’m able to confirm with greater conviction since I steeled myself and ordered a buffing arbor from LMI in the U.S. Used together with two grades of Menzerna buffing compound, buffing is now an easy task, and the gloss I’m able to achieve effortlessly is pretty impressive. My wallet may be lighter, but my finishes have improved out of sight as compensation.

Of course, with any finish material there are trade-offs and compromises and KTM-SV is perhaps no different in that regard. One of KTM-SV’s supposed disadvantages is that, unlike Target’s EM6000, once it’s cured, subsequent coats don’t burn into the preceding ones meaning that invisible finish repairs are difficult to achieve. I’ve come across some conflicting advice, however, which says that rubbing the area to be repaired with acetone or lacquer thinner softens the finish enough to allow an invisible repair, but I have no first-hand experience where that’s concerned and can only repeat here what I’ve read elsewhere. Less significantly in my view, it’s said that it can’t be buffed to as high a gloss as nitro, although I’m pretty happy with the gloss level on the guitars pictured. The only other real negative - which I'm all too used to living in Australia - is that freight from the U.S. is more costly than the material itself.

The guitars pictured in my last two posts were finished with KTM-SV top coats over epoxy pore fill and three seal coats of de-waxed white shellac. I followed the finish schedule described by Randy Muth in a thread on the OLF, whose prescription is for six coats per day over two days, with the exception of the soundboard which receives two coats fewer for a total of ten, i.e., only four coats on the second day. Following Rolfe’s suggestion, I added 30ml of distilled water to my quart tin of KTM-SV which seemed to help with flow-out and leveling, although it’s also possible that the coats began to lay down more smoothly for me as my novice spraying technique improved; by the time I applied the last top coats on the second of these guitars, it was laying down beautifully, to the extent that I was able to begin my level-sanding with 800-grit paper.

Interestingly, Rolfe also remarks that there’s very little shrink back as the finish cures, however, I notice that minute ridges corresponding to the grain lines are evident on both tops; in fact, it looks a lot like a typical thin nitro finish which isn’t necessarily a bad thing given that for many, nitro is still the standard by which all other finishes are judged. As best as I could determine with dial calipers, my ten coats on the soundboard measured around 0.1mm, or 4 thou in thickness after leveling and buffing – a very crude guide to be sure, but nevertheless helpful in the absence of any more accurate means of measurement.

At some point I may try Target Coatings’ EM6000 (Stew-Mac’s Colortone Waterbase Lacquer) purely for the sake of comparison, but for the foreseeable future I’m a KTM-SV convert, and greatly relieved to have at last a found a finish product which allows amateurs like me to produce near professional results without the bother and expense of a spray booth, explosion-proof fan, etc. I know I could cross my fingers and shoot nitrocellulose in the back yard as many others do, but I’ve been there and done that and as I’ve grown older, a little wiser, and a lot more conscious of health and safety issues, I’ve decided not to repeat that experience and expose myself and others to the attendant risks. Like a reformed smoker, I’m still tempted at times to ignore the risks and revert to past practice, but I’m confident that good sense will prevail on both counts!

Some relevant links:

KTM-SV – An Overlooked Finish

KTM-SV Finish for Wood

Official Luthier's Forum discussion

Cheers

Pete

Notable Firsts

This is a guitar project I've had very little time to work on lately, but with the Australian blackwood/Sitka spruce triple-O featured in my last post about to head off to its new home, I delude myself with the notion that with one less guitar to complete, this East Indian rosewood/Engelmann spruce effort is somehow closer to completion too.

With a side soundport and a Florentine cutaway, there are some personal firsts for me with this instrument. This has also been my first experience using Grafted Coatings' "other" water-based finish, KTM-SV, which I've written enthusiastically about in earlier posts. KTM9, Grafted Coatings' previous foray into water-based finishes, was successful up to a point and still has its advocates, but there have been enough negative reports over the years that I eventually discounted it as I considered a switch to sprayed finishes. I think it's fair to say that in many people's experience it hasn't stood up well to normal wear and tear or, most alarmingly, to the corrosive effects of some people's perspiration. To date, I've read no reports of a similar nature regarding KTM-SV - fingers firmly crossed!

The soundport is an increasingly popular feature and proved a simple addition, which perhaps accounts for the fact that some professional builders offer it as an option at no additional cost. Adding the port is a relatively easy task which I completed once kerfed linings had been glued around the rim and the back had been attached to the sides. The guitar sides diminish gradually in depth as they approach the neck area, and it was easy to glue in a similarly tapered veneer laminate to wedge snugly between the linings as cross-grain support in the area of the port. I chose a simple oval soundport which was marked on the outer face of the side with the aid of a flexible plastic template and a white ball-point pen. I used my Dremel and a tiny circular saw blade to roughly cut through the side and the backing laminate well inside the line, then sanded to the line with the Dremel and a mini sanding drum.

The cutaway presented a more formidable challenge, with much head-scratching and several sleepless nights required before a plan of attack was formulated. Bending the cutaway section of the side on an electric bending iron was easy enough, but binding the point of the cutaway proved a little trickier; I chose the ambitious approach which was to mitre the joints in three dimensions. The outcome wasn't perfect, but having now negotiated the process more or less successfully, I can see ways to improve the end result next time around. Generally, it's only after I've addressed a problem and found myself unable to identify a potential solution that I become temporarily dejected and briefly contemplate other less taxing hobbies!

Cheers

Pete

Reaching the Finish Line - KTM-SV

I've made significant advances with many aspects of guitar construction in the recent past, but achieving a quality finish has proven to be a persistent frustration as well as one of the last major hurdles. It's especially pleasing then to be able to report that the finish used on this guitar - Grafted Coatings' KTM-SV - has proven to be a watershed where confidence in the standard of my guitars is concerned.

While there's still plenty of scope for further improvement of my skills and knowledge - most noticeably in the area of fretwork and setup - I'm quietly confident that my guitars are approaching a standard comparable to that of other fledgling independent builders. If I ever make the leap and decide I'm ready to sell my guitars, the prices I ask will of course reflect this cautious assessment!

Finding a finish product which works for me is cause for celebration, but rubbing it out to the high gloss that guitar owners expect has been yet another challenge. Thankfully, after taking the plunge recently and ordering a buffing arbor from LMI in the US, I'm pleased at last to be able to bid farewell to the more laborious hand-polishing methods. Not only was it an onerous task, but I was never entirely satisfied with the end result. With motor-driven buffing wheels and two grades of Menzerna dry buffing compounds at my disposal, the process is an absolute breeze and the gloss I'm now able to achieve reduces the pain of having purchased a hefty piece of equipment from overseas. International freight charges - as always - are a real headache!

I guess some vital statistics are in order:

• Back and sides: Australian blackwood
• Soundboard: Sitka spruce
• Neck: Queensland maple
• Bridge and fingerboard: ebony
• Bindings: ebony
• Frets: EVO gold
• Tuners: Gotoh 510 minis
• Rosette and fingerboard inlay: paua abalone
• Finish: Grafted Coatings KTM-SV
• Scale length: 24.9"

Click any of the photos for a larger view.

Cheers

Pete

Double-Standards

What a strange set of standards we apply when it comes to wood. Where backs and sides and, to a lesser extent, soundboards are concerned, we are happy to pay a premium for colourful, unique or highly-figured woods. According to tradition though, components made from ebony must be jet black and are graded and priced accordingly. We can even buy dyes especially for the purpose of reducing interesting, streaky ebony to a boring, homogeneous black!

The ebony headplate pictured was rated as "second-grade" material, presumably because it wasn't boring enough. Make up your own mind!

I've applied a first seal coat of shellac on this neck and will spray another two before allowing it to cure overnight. Once the finish coats of KTM-SV have been sprayed, levelled and polished, I'm confident this ebony will look much better than second-grade!

Cheers

Pete

In Pursuit of a Glossy Finish

Without access to a buffing wheel, it's a case of gritting my teeth and rubbing out the finish on this guitar using more tedious methods. It's a good workout if nothing else!

I was careful to level the finish thoroughly as the spraying of the 12 top-coats proceeded. As a result, it was a relatively easy task to carry out the final levelling with 800-grit wet-or-dry paper and water once the finish had been allowed to cure for a few days. To allow for the curvature of the guitar's surfaces - including the domed top and back plates - I wrap my abrasive paper around a small rectangle of cork floor tile. The cork provides a solid backing for the paper but has just enough flex to conform to the curves. I've had better results since I began sanding with the grain, the significance of which is that by sanding in one direction, the sanding scratches seem more easily removed by the grade of paper to follow.

Other water-based finish products require that mineral spirits (turpentine) be used when wet sanding, however, I detest turpentine for any application and it's a blessing that KTM-SV can be safely wet-sanded using water as the lubricant, - the proviso being that it's been given time to cure. It's become very clear to me that a little extra time spent sanding thoroughly through 800, 1200, 1500 and 2000 grit papers to remove sanding scratches before the polishing compounds are brought into play makes a high gloss much, much easier to achieve. If you noticed the large gap between 800 and 1200, it's only because my usual local sources seem to have run out of 1000-grit paper temporarily. Sanding is a tedious task, but I found that reaching for the polishing compounds too soon invariably saw me return to wet-sanding soon afterwards when polishing revealed remnant sanding scratches - there are NO short-cuts!

As I mentioned in an earlier post, I use Autoglym's 03B Fine Abrasive and 02B Ultrafine Renovator once I'm done with sanding. With limited experience with sprayed finishes, I'm still pretty tentative when it comes to levelling and polishing for fear of rubbing through the layers of finish to the wood and, although a random-orbital sander equipped with hook-and-loop Surbuf pads helps with the polishing to a degree, I've been careful to stay away from the perimeter of the guitar's top and back plates as well as the edge of the soundhole, the area of the side soundport and the cutaway region while using it. As a result, I'm left with the option of a cork-backed sanding block wrapped with a polishing cloth to rub out these areas. It's not a difficult job, but patience and persistence are valuable assets - ones I wish I had in greater measure!

Click on any of the photos for a larger view.

Cheers

Pete