Irish Bouzouki - Fun With Moulds

Making jigs and moulds is a messy and time-consuming affair. There are definitely more enjoyable ways to spend one's time, so I figure it's worthwhile investing a little extra effort and expense to get it right the first time.

Half-body and full-body templates, with headstock template

While I wait for suitable weather and a break in my IT work long enough to afford me the opportunity to spray finish coats on the four guitars I've been constructing (seemingly forever!), I'm taking the first steps in building an Irish bouzouki - a first for me. After deliberating for some time where design and dimensions are concerned, fabrication of an outside body mould and templates for the bridge and headstock have been my focus in spare moments over the past couple of weeks.

Where construction of the body mould was concerned, my first task was to decide on the overall dimensions in the absence of any universal standards. In the guitar world, the iconic factory models manufactured by Martin and Gibson for many decades have at least served as a loose benchmark for the independent builder. However, as the Irish bouzouki was appropriated to a large extent from the Greek instrument and randomly modified to suit the requirements of a motley band of Irish folk musicians, its evolution appears to have been driven less by tradition than by the whims of the builders and musicians who have adopted it. It seems there are any number of combinations of scale length, body shape and body dimensions in common use, and I finally decided that in the absence of any agreed formula I'd develop something largely on what appeals to my aesthetic tastes. I was influenced a little too by the length of the truss rods I have on hand, my available fretting templates, and my concerns that an extreme scale length and a body join at the 17th fret - as is common practice - would result in a cumbersome, neck-heavy instrument. For better or worse, I've decided on a more conservative 632mm (24.9") scale length, a body width of ~350mm (14"), and a neck to body join at the 15th fret.

Using a set of French curves and a flexible ruler, I tidied up the half-body outline I'd drawn freehand on paper so that the curves transitioned and flowed smoothly. I traced the final outline onto a piece of baking paper, then transferred the outline to a piece of 6mm (1/4") MDF using transfer paper sourced from an art supplies shop.

I jig-sawed the MDF just inside the body outline I'd transferred from the tracing paper, then carefully removed the rest of the waste up to the line using a spindle sander. This yielded me a half-body template that would guarantee symmetry when used as a routing master. To fabricate the full-body master template, I aligned the centreline of the half-body template to a line I'd ruled on a second piece of 6mm MDF, traced the body outline and jig-sawed within the line, then clamped the two pieces together and routed to the line with a flush-cut router bit riding along the inner edge of the half-body template. Flipping the half-body template over and again carefully aligning the centrelines, I routed the other half in a similar fashion. The half-body and full-body templates are shown above.

I know from experience what a dusty mess MDF makes when machined, and of its tendency to deform and deteriorate over time, and made the decision to spend a little more money and fabricate the outside body mould from ply. To do so, I traced inside my full-body template onto a piece of 18mm ply, then jig-sawed inside the line leaving a small margin. Once again, having carefully aligned and clamped the full-body template in place, a flush-cut router bit removed the remaining waste.

I've struggled in the past to accurately align the individual layers when fabricating new moulds, and the solution - now that it's dawned on me - seems embarrassingly obvious. On the second layer of ply, I once again jig-sawed inside the pencilled body outline transferred from the full-body master template, then aligned and glued the two layers of ply together. It was then a matter of routing the waste to the line on the second layer of ply using the first layer itself as the bearing surface for the flush-cut router bit. The process was repeated for the third and fourth layers, with the final mould therefore comprised of four perfectly aligned layers of ply yielding a total thickness of 72mm.

Useful links:
Graham McDonald's, "The Bouzouki Book"
Nigel Forster Guitars - Irish bouzouki page

Cheers
Pete

Fretboard Binding

Gluing the purfling to the binding before it's attached to the fretboard edge seemed to be the most logical approach when I began binding my fretboards, but I found it a challenge to accurately align the lower edge of the purfling with the underside of the board, no matter how careful I was when gluing and clamping it in place.

I managed to achieve acceptable results on the first couple of bound fretboards, but was uncomfortable with the process and felt there must be a better way. After dwelling on the problem off and on for a while, it occurred to me that I could just glue the binding on first - sans purfling - without fussing too much about aligning its lower edge exactly.

To solve the problem, I've knocked together what could best be described as a mini router table. With my laminate trimmer clamped in position from below, and a makeshift fence in place, I make some test cuts on scrap, adjusting the trimmer so that the rebate cut by the router bit will be the exact depth of the purfling strip. The width of the rebate isn't quite as critical, as long as it's less than or equal to the width of the purfling - any overhang can be trimmed off later.

Having set up the trimmer and fence, it's a simple matter of running the bound fretboard along the fence to accurately form the rebate for the purfling. The curved sections at the soundhole end of the board deserve some special treatment, but they're easily addressed using a similar approach.

All that remains is to glue the purfling strips into the rebate, with help from the same clamps used to glue kerfed linings strips in place. The purfling at the soundhole end of the fretboard is mitred to achieve a neat look.

I'm sure there are other equally effective methods, but this one works for me!

Cheers
Pete

Fingerboard Inlay

I think it's a commonly held view that for the majority of players, traditional fretboard markers provide little practical benefit (the markers on the fretboard edge are a different story), but I can't quite bring myself to leave the fingerboard totally devoid of decoration. Having said that, my ambitions where inlays are concerned are modest indeed, and while there's no denying the skill and sheer artistry displayed by the likes of Larry Robinson, Grit Laskin and Jimmi Wingert, I have no desire to emulate them - even if I thought I had the ability and temperament to do so.

The abalone and pearl inlay I've come to regard as my own was originally inspired by the decorative elements found on Bob Benedetto's arch-top guitars, but has evolved over time to the extent that my conscience is now clear - I no longer view it as imitation. I'm not adept at distilling design ideas down to abstract representations - I'd fail miserably at logo design, for instance - so whatever I dream up tends to be fairly representational. Where my fretboard inlay is concerned, I've stretched those personal limitations ever so slightly, but it's still blindingly obvious that the inlay represents a single flower flanked by two leaves.

I draw the shapes freehand, directly onto the pearl and abalone blanks, then cut the pieces out with a jeweler's saw. I don't feel the need to be terribly careful as I cut, knowing that the shapes of the individual pieces lend themselves to clean-up and refinement on my spindle sander. I'm quite happy for the exact shape to vary from guitar to guitar; given that I strive for accuracy and consistency where every other aspect of the guitar is concerned, it's nice to introduce some elements that have come into being by a more organic process.

My Dremel has its shortcomings and limitations, but it's an appropriate tool with which to route the inlay cavities. I need to keep the cavities free of wood dust as I proceed, and the solution is provided by an aquarium pump running alongside me on the bench. The outlet hoses from the pump are taped to one of the pillars on the Dremel base, and direct a constant stream of air onto the work. They disperse the ebony dust as soon as it's produced, which helps maintain a clear view of the lines I've previously scribed around the individual inlay pieces.

Using tiny spiral downcut router bits, I can cut accurately up to the lines, with a scalpel blade and my smallest chisel tidying up the corners that were too tight for the router bit to deal with. The inlay experts would have me believe that it's prudent to undercut the edges of the inlay cavities with a ball-end bit, but my inlay is so simple, and my results to date of a decent enough standard, that I haven't found it necessary to explore that option. If I've been careful enough, any gaps between the inlay and the walls of the routed cavity are insignificant. Those that are evident are easily hidden with matching wood dust and a drop or two of thin cyanoacrylate (CA) glue applied after the shell pieces have been glued in place. Of course, it helps that ebony is very forgiving in this regard!

Cheers
Pete

Fitting the Back

Perhaps there's some aspect of successfully fitting the back that represents a significant milestone along the way to completing a guitar, or maybe it's just that I've repeated this part of the process enough times that I feel confident in the outcome and have come to enjoy the sensation and sound of the back braces clicking neatly into their pockets. Whatever the reason, it's a part of the build process I look forward to and derive great satisfaction from.

To reach this milestone - assuming that the dome of the back has already been sanded into the rims - I carefully align the back with the centres of the head and tail blocks, then mark the sides where the brace closest the the tail block will intersect them. I lay a steel rule across the guitar to join the corresponding marks, and pencil the line of the braces onto the top surface of the linings. 

As a precaution against chipping, I make a saw cut equal in depth to that of the brace end on the side of the pocket likely to be chipped by the clockwise rotation of the bit. I hope the right-hand photograph below shows this clearly.

With a spiral downcut bit mounted in the Dremel and carefully adjusted for depth, I rout the first pair of brace pockets, using the pencil lines as a guide. If the marks were placed accurately, the braces slip into place with just a hint of resistance. I check the fit of the back and widen the appropriate brace pocket to compensate for any misalignment. Once I'm happy with the fit and alignment, I can mark the next pair of brace pockets, confident that the alignment of the back will be more securely and accurately established as I proceed. When the four pairs of brace pockets have been prepared and the back fits perfectly, I can allow myself a moment of self-congratulation - before I remind myself that it's really only a minor triumph and that there's plenty of work ahead of me!

Cheers

Pete

The Modified OM

With the messy job of constructing a new bending form and outside mold finally out of the way, I've been able to make some progress on this guitar over the past week.

The walnut sides bent willingly, as they always do, and I was pleased to see that they conformed closely to the new mold, with the exception of some minor spring-back on one of the lower bouts. The spring-back was a useful reminder that it's advisable to subject the sides of any wood species to a couple of heating and cooling cycles before removing them from the bending form. I have to try hard to resist my innate impatience, and on this occasion I was a little premature in taking the second side out of the side bender, hopeful that such a compliant wood wouldn't require a second cycle. A quick touch-up on the electric bending iron soon had the side sitting obediently in the mold.

With the head block, tail block and kerfed linings glued to the sides, I'm better able to assess the new body shape. Needless to say, I'm greatly relieved that it matches my expectations, and that the time-consuming and incredibly dusty task of making yet another bending form and outside mold has been averted.

Noting the recent emergence of guitars referred to as "modified dreadnoughts", and lacking a more imaginative idea, it seems reasonable to dub my new guitar model the "modified OM"! 

Cheers

Pete

Kerfed Linings

I've fabricated kerfed lining strips from mahogany in the past, and while that's a popular and appropriate choice, on this guitar I was in the mood to use linings that closely match the colour of the spruce back braces. Spruce doesn't exactly grow on trees in my neck of the woods (puns intended), so I substituted Jelutong - a lightweight, light-coloured South East Asian hardwood species that serves this purpose well.

After bandsawing and thickness-sanding the strips, I set up a crude but effective jig on the bandsaw that helps me cut kerfs of a consistent spacing and depth. I leave a little more wood between the extremity of the cut and the opposite face of the lining than it seems is common with the off-the-shelf product, and the strips I prepare are a little more robust as a result. If there's any trade-off, it's that I feel the need to pre-bend the waist and upper bout portion of the linings on my bending iron prior to gluing them in place, more as an added precaution against breakage than out of any real necessity. 

A pet peeve, and the motivation for devoting a little time to preparing my own snap-resistant kerfed linings, is seeing an otherwise carefully crafted instrument whose linings are joined at some point, particularly when such joins are in plain view through the soundhole. Sacrilege!

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

Saddle Slots and Bridge Pin Holes

Although I'm nowhere near ready to make use of them, I've spent some time lately working on the bridges destined for the two guitars I have under construction for no other reason than it's a job I can devote short periods of time to in a spare moment, or treat as light relief between more demanding or time-consuming tasks.

To facilitate drilling of the bridge pin holes in a perfectly straight line, parallel to the saddle slot I've previously routed out, I glue a small wooden block to the front edge of the bridge blank on the treble end prior to cutting the bridge outline. I trim the block carefully using my disk sander so that as the bridge is slid along a makeshift fence attached to my bench drill's table, the centre of each hole will be equidistant from the slot. Having guaranteed alignment in that direction, I need only take care then to align the bit with the string spacings marked on the bridge as I prepare to drill each hole (a white ball-point pen is a godsend when marking dark woods like this ebony). A brad-point bit makes accurate alignment much easier and produces a perfectly clean hole provided it breaks out through the lower surface of the bridge into a backing board of MDF or scrap timber.

With the bridge pin holes drilled parallel to the line of the saddle, there's a consistent break angle for the strings as they pass over it. While some reason that this guarantees an equal downward string pressure along the saddle's length, the fact that string gauges and tensions vary from string to string casts doubt on the validity of that argument. A slight increase in the saddle's height towards its centre and the potential use of radically altered tunings such as "Orkney" tuning (CGDGCD low to high) complicate the matter still further. Whatever its other merits though, it's a neat look and I'm assured of adequate downward pressure on the saddle and therefore good transference of the strings' energy to the soundboard.

It seems there's no hard and fast rule where bridge weights are concerned; popular wisdom has values falling within a fairly wide range. Given that there are a multitude of factors influencing the guitar's sound, I somehow doubt I'll ever build enough instruments to draw any meaningful conclusions where small variations in bridge weight are concerned; there are so many other variables likely to have a more significant and measurable effect should I feel the urge to experiment. That being the case, I'm happy to aim for a more or less consistent bridge weight from one guitar to the next. With ebony bridges such as these, I shoot for a weight of between 30 and 35 grams, making use of a cheap digital gram scale as I shape and shave the bridge wings to their final thickness.

Useful links:
Routing the Saddle Slot

Cheers

Pete

Hand Tools: Out With the Old, In With the New

I've known for a long time that guitar building will be an activity I'll pursue until failing eyesight, a wayward bus or the grim reaper himself finally put an end to my efforts. Despite that certainty, I've always had great difficulty parting with my hard-earned cash to build a collection of high quality hand tools - second-hand shops and flea markets have been the source of many of them until recently.

I've justified my tight-fisted attitude by reasoning that spending five times as much on a decent hand plane, for example, would be unlikely to result in a corresponding five-fold improvement in the standard of my instruments. While there's still truth in that argument at a superficial level, thinking a little more deeply on the subject leads me to conclude that there are other more subtle benefits to owning quality tools beyond their ability to perform their intended function so much more effectively than the poor substitutes I've made do with in the past. 

In fact, finally clicking the "Buy Now" button on a set of LMI's chisels and a couple of Veritas hand planes - a low-angle jack plane and a #4 smoother - has been beneficial on many levels.  The simple fact that my chisels and planes are now of a much higher quality has instilled a sense of pride in their ownership - a new and pleasurable experience!  That in turn has added to my enjoyment of the job at hand which in itself can only have a positive effect on the standard of my work.  I might also add that acquiring quality tools and experiencing the warm glow their ownership brings has provided the incentive to develop a much more disciplined approach where sharpening is concerned - I've been pretty lazy in the past on that score.

When I'm about to undertake a task demanding the utmost care and attention to detail, I find that clearing my workbench of its usual accumulation of tools and firing up the shop vacuum seems to unclutter my mind as well as my immediate work area; I seem better able to concentrate and my chances of success with whatever task I'm about to begin seem vastly improved as a result.  I'm finding that the joy of using a well-tuned, good quality plane or a sharp, finely made chisel is having a similarly positive effect on my attitude and ability to focus.  Any doubts I might have had brought about by the not-insignificant cost - including the predictably horrendous shipping charges from the U.S. and Canada - are fading rapidly.  Besides (I tell myself!) my amateur status shouldn't stand in the way of my pursuit of professional results.

If there's a downside to all this - other than the hit my wallet has taken of late - it's that I can no longer blame poor quality tools for any work I judge to be less than perfect!

Cheers

Pete