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Category Archives: musical instruments

Before gluing up the joint, it’s worth taking some trouble to make sure that the two parts fit perfectly. I put the neck in a vise and hold the headstock in place while checking for gaps with a 0.05mm feeler gauge. A bright light behind the joint also helps to reveal places where the fit is defective.

Here I’ve discovered that the sides of the V are a bit loose…

…while the shoulders are tight.

A couple of fine shavings taken off the shoulders of the headstock using a shooting board…

…improves the fit. As a final check, I rub chalk over the male part of the V joint, locate the female part in position and press the joint together hard.

Where the fit is perfect, chalk will be transferred evenly. High spots, on the other hand, show up as a blotch of chalk surrounded by unchalked wood. Here it looks as if there’s a high point on one side near the mouth of the V.

A small file takes off the bump…

…and a second chalk fitting shows that the joint fits pretty well all over, except for a small low spot on one side at the apex of the V. I decide that I can live with that.

The next step is to dust off the chalk, size all mating surfaces of the joint with hot dilute hide glue and leave them to dry.

This is the clamping arrangement that I use. It’s important that the compression force runs through the centre line of the headstock and bears directly on the shoulders of the joint. Chiselling off the front of the V where it projects through the headstock allows the bar of the clamp to sit close to the surface of the headstock.

Once I’m happy that I can get the clamp into exactly the right position, I un-clamp, brush medium strength hide glue onto all joint surfaces, re-clamp it and leave it undisturbed for a couple of hours.

Here it is after taking the clamp off. The shadow below the right hand shoulder of the joint indicates that the headstock is slightly twisted relative to the neck. I suspected that this would happen while I was making the final adjustments but decided that the inaccuracy would be small enough to plane it out after the joint was glued up.

And I’m pleased to say that it was.

The back of the joint looks a bit weird until the extra block is shaved off.

But these two necks show that it comes out all right in the end. Even with a magnifying glass it’s scarcely possible to see that extra wood has been added and after the final shaping it will be quite invisible.

That’s the last of the series of posts on making a V joint. Thanks to anyone who has followed the story this far. Before finishing, I ought to add that there are many variations in the way this joint can be cut. Some makers, for example, prefer to use a template for marking out rather than a ruler and dividers. Please add a comment if you know how to do it quicker or better.

Click on the thumbnails below for larger pictures.

Moving on from my previous post about marking out a V joint, it’s time to cut and trim it to shape.

First, I saw out the V in the headstock, keeping close to the lines but being careful not to saw past them. I try to be brave in sawing up to the line at the narrow end of the V because that’s the hardest part to clean up later.

Next, I stop to put a fresh edge on the chisel that I’m going to use. When it will slice through tissue paper, I reckon that it’s sharp enough.

I clean up the V, paring from both sides towards the middle. Final cuts are carried out with the chisel resting in the knife line that marked out the joint. A small square is useful to check that the sides of the V are flat. The most difficult part of the joint is the apex of the V but a slicing cut with the corner of the chisel will remove the last bit of waste.

Here’s the female part of the V joint in the headstock finished. It shouldn’t be necessary to touch it again.

Now I cut the male part of the joint on the neck, starting with the angled shoulders. I chisel out a ramp for the saw in the usual way…

… and then saw down to the V, keeping clear of the lines.

I mark the starting point of the cuts for the sides of the V on the endgrain…

… place the neck in a vise, tilting it so that the cut will be vertical, and …

saw off the sides of the V with a tenon saw.

I mark and keep the pieces that I’ve just sawn off. They’ll be useful later.

Now I clean up the V and its shoulders with a chisel, paring in from both sides as I did for the headstock.

Here it is almost finished.

The neck and headstock are now tested for fit. Below is the view from the fingerboard side of the neck.

And here’s the view from the back of the neck.

As you can see, there’s a problem at the apex of the V, where a shadow shows that the neck isn’t quite deep enough to fill up the whole of the female part of the joint in the headstock. (My stock of mahogany for necks is planed up at a thickness of 25mm which means that I always run into this difficulty.)

The solution is to add a little extra depth at the apex of the V. This is where the offcuts that I saved come in handy. I prepare a small piece from one of these…

and glue it on, taking care that the direction of the grain in the extra piece is orientated in the same way as the grain of the neck.

When the glue is fully hard…

… it’s sawn roughly to shape…

… and trimmed with a chisel. This addition will be invisible in the completed joint.

The last step is to make sure that everything fits to perfection before glueing up. I’ll discuss how to do that in the next post.

Click on any of the thumbnails below for larger pictures.

Although the geometry of the V joint is simple, it’s surprisingly hard to to visualise if you’ve only seen the joint on a finished guitar. So, in an attempt to make the marking out easier to understand, I’ve sketched it below.

As with all joints, the more precisely it’s marked out the better the final result. It’s crucial that the stock is sized and squared up accurately. The headstock needs to be 17 or 18mm thick to give a final thickness of 19 or 20mm after application of the veneer. The neck must be rather thicker – at least 24 or 25mm – or there won’t be enough wood at the apex of the male part of the V where it engages with the female cut out part in the headstock. The side view in the drawings of the joint above will show what I’m getting at. (Even 25mm thickness may not be enough for full engagement but I’ll show how I deal with that problem in my next post.)

It’s also important that the end grain edge at the lower end of the headstock is exactly square to the sides and faces. I ensure this with a low angle plane and a shooting board.

To begin the marking out, I scribe a centre line down both faces of the headstock with a marking gauge, being careful to scribe both faces from the same edge.

Then I mark the corners of the V with dividers, placing points 18mm either side of the centre line to form the base of the V, and a single point 42mm up from the base on the centreline to define the apex. In the photograph, the pinpoints are marked with chalk to make them more visible.

A single bevel marking knife is used to mark the sides of the V, keeping the ruler on the outside of the V. I try not to cut beyond the point of the V, particularly on the back of the headstock. It doesn’t matter so much on the front which will be covered with veneer later.

To ensure that the ruler doesn’t slip, it’s helpful to fix a strip of fine sandpaper to its underside with double-sided tape.

Here’s the V marked out on one face of the headstock. This process needs to be repeated on the other face so that both sides of the headstock are marked. I haven’t bothered to illustrate this.

Now it’s time to mark out the male part of the joint on the neck. Again, I start by scribing a centre line down both faces. Then I square a line across the upper face of the neck slightly more than 38mm from the end.

Using a sliding bevel set for the angle that I want the headstock to make with the neck (10º in this case, so the bevel is set to 80º) I scribe both sides of the neck from the line that I’ve just squared across it.

Then I square across the back of the neck at the point where the angled lines on the sides end. Finally, I mark out the V on both faces using dividers set to exactly the same dimensions that I used on the headstock. The only difference is that, when it comes to scribing the lines with the knife, I keep the ruler on the inside of the V.

Here’s the top of the neck marked out…

…and here’s the back. You can see that, on the back, the V is positioned slightly further down the neck than it is on the front.

In the next post, I’ll show how I cut out the joint.

You can see larger versions of the photographs by clicking on the thumbnails below.

There are two ways to create the angle between the headstock and the upper end of the neck of a guitar. One is to saw it out whole from a large piece of wood; the other is to make it out of two pieces using a glued joint – either the V shaped joint invented by the early guitar makers or a scarf joint. Of these options, the most rational is the scarf joint. It’s quicker and easier to execute than a V joint and wastes less wood than sawing out a neck and headstock whole. What’s more, it has a large glued surface so it doesn’t rely on nanometric accuracy for its strength.

Despite the obvious advantages of a scarf joint, the V joint has become something of a fetish among guitar makers. This is easy to defend where historical accuracy is concerned. After all, if you’re attempting a copy of a 19th century guitar, it’s desirable – even obligatory – to imitate the constructional methods of the original maker. But for a modern instrument, why prefer a weaker joint that takes longer to make?

The answer, I guess, is to show that you can. It’s not a million miles away from the Georgian cabinet makers who made the pins of their dovetails so skinny that they almost vanished at the narrow end, as you can see in this photograph of the drawer of the table at which I’m sitting as I write this post.

There’s no practical advantage either in strength or speed of production in cutting dovetails like this. Indeed, the reverse must be true. But they do provide an understated way by which makers can demonstrate that they care about seldom seen details and show off their skill.

I’ve found myself using a V joint for both these reasons. Here’s a copy of a 19th century guitar that I’ve mentioned in previous posts. The V joint in this instrument was present in the original and it seemed right to keep it.

On the other hand, the V joint in the guitar below could perfectly well have been a scarf joint. The guitarist for whom I made the instrument didn’t notice it until I drew it to her attention. Still, I enjoyed making it and, for reasons that I can’t properly explain, felt that it was worth the extra time and trouble.

I’ve just cut a couple more V joints for guitars that I’ve got planned for 2012 and, although instructions for making this joint already exist (see here, for example), I thought it might be useful if I kept a camera handy to document the process. In the next post, I’ll explain how I mark out the joint.

In his book Violin Restoration (ISBN 0-9621861-0-4), Hans Weisshaar has a photograph of a self-adjusting jig that will hold violin bridges while they’re being planed. I was rather taken by the simplicity and ingenuity of the idea and I thought that I’d make one to see if it worked any better than the very basic holder, shown below, that I use at the moment.

The clever part about Weisshaar’s jig is that one side is free to rotate which means that it can adjust itself to fit bridges of different geometry, holding them all equally tightly. It’s easier to show how it works with a few photographs than it is to describe it.

Extra holes allow the swivelling side to be mounted closer to the fixed side to accommodate three-quarter and half size bridges.

A small block glued to the bottom helps to hold the jig against the edge of the bench or in a vice.

Although the device works well, it’s probably not going to be much use anyone except a violin maker. Still, I thought that the idea of using a freely moving arm or jaw to grasp pieces of wood when the sides aren’t parallel had wider applicability. You might be able to use a scaled up version for planing tapers on table legs, for example. And the accessory jaw for holding tapered shapes in a vice that’s shown on the Tools and Jigs page of this site (scroll down to the second item) draws on the same principle.

 
 
 

Larger versions of these photographs are available by clicking on the thumbnails below.

Violins are difficult to photograph but, thanks to Michael Darnton’s book on violin making, I’ve recently got better at it. As far as I know, the book isn’t published (or even finished) yet, but some chapters are available on-line. There’s one on violin photography which, amongst other good advice, mentions the ingenious technique of using a glass jar or tumbler to stand the instrument on while it’s being photographed. This is less precarious than it seems and has the great advantage of holding the violin vertically upright in a way that’s nearly invisible.

 

 

Previously, I’d used this stand, which is fine for displaying instruments but much less good than the glass method when it comes to photographing them.

 

 

Here are a couple of shots of a recent violin. They’re still not very good – the lighting is uneven, shadows are visible on the backdrop and the camera is positioned a little too high – but they’re a substantial improvement on anything I managed before.

 

 

The violin is based on an instrument made by Carlo Bergonzi in 1736 but I’ve made it three-quarter size for a violinist who, following an injury to her shoulder, can no longer play a full size fiddle comfortably.

 

Although I was sure that I’d read somewhere that there was a way of using a mirror to help judge when a drill bit was truly vertically, I struggled to find an account of how it was actually done. Eventually, after a lot of googling, I came across this letter and illustration published in Popular Mechanics nearly 80 years ago.

To find out if it worked, I bought a cheap handbag mirror.

First I cut off the hinge and trimmed back the plastic mount along one edge.

Placed next to the drill bit, the mirror showed when the drill was vertical…

… and when it wasn’t.

It’s a simple idea but I was impressed by how well it worked. A problem though, is that the mirror only tells you whether the drill is vertical in one axis. You have to move the mirror around the drill to check whether it’s vertical in the other axis and while you’re doing this, it’s easy to lose the vertical on the first axis.

One solution might be to have an L-shaped mirror or, perhaps better still, a mirror with a hole in its centre. Then, all you’d have to do to check that the drill was truly vertical in both axes would be to move your head.

So I ground a small hole in the centre of the other mirror and tried it out.

This is the view when the drill is vertical.

And when it’s miles off.

Of course, you don’t need a mirror to see when the drill is as far out as that. The benefit is that it makes it easy to spot small deviations from vertical.

Does it work in practice? As a test, I drilled ten 2mm diameter holes at 10mm intervals along a line in a piece of MDF and stuck cocktail sticks into them.

Not perfect – but not bad either. Certainly better than I was able to do in a repeat of the experiment when I used a small try square instead of the mirror as a guide, as you can see below.

Obviously, the best way to drill a truly vertical hole is to use a drill press. But there are occasions when this is impossible because the work piece is too large or too awkwardly shaped. It’s then that this trick with mirrors might come in handy.

A trip this summer took me to Stein am Rhein in northern Switzerland, where I visited the museum of the abbey of St Georgen – a place both fascinating and frustrating. Fascinating because of the interest of the buildings and their contents. Frustrating because there was so little explanation: no convincing narrative about how or why the place, which ceased to be a religious foundation 500 years ago, still exists.

Even so, it contained several things to interest woodworkers. Here are three: the first was this enormous wine press which, if the carving on the main beam is to be believed, was built in 1711. Maybe it’s an attraction of opposites but, as an instrument maker who has to fuss about tenths of a millimetre, I couldn’t help thinking what fun it would be to chop out mortices and tenons on this sort of scale.

The second was this fine chest decorated with paint and chip carving. It too, had a date carved in it – 1697, just visible bottom right – which seems plausible enough. But what on earth was it doing in an abbey that had stopped functioning as an institution during the reformation in the early 1500s?

The last was this remarkable repair to the bottom of a pine cupboard. Rot and wood worm must have got into it, but someone thought that that it was worth saving and, perhaps inspired by the Alps which aren’t too far away, scarfed in a new footing. I’d never seen anything like it. Please write if you know of other examples or can explain more about the technique.

This splendid photograph was taken by John Runk¹ in Stillwater, Minnesota on an 8 x 10 plate camera in 1912. I came across it in a book, The Photographer’s Eye written by John Szarkowski. Unless the chap in the hat is unusually short, these pine boards must be around 3 feet wide and 15 – 18 feet long. The saw marks run straight across the boards which made me wonder how they had been cut – not with a circular saw obviously. Were large bandsaws in operation at the beginning of the 20th century?

Buying wood a few months ago, I realised that I didn’t know much about modern methods of conversion of timber either. Here are a couple of photographs taken in Andy Fellows’ wood store in Gosport, Hants². He has supplied me with quite a lot of the wood that I’ve used in recent guitars including the Madagascan rosewood for this nylon string guitar and the beautiful walnut for this copy of a 19th century guitar by Panormo. These boards aren’t quite as large as those in Runk’s photograph but they’re still pretty big and I’ve only the vaguest idea of how he goes about transforming them into the book matched guitar sets from which he lets me pick and choose. Next time I visit, I shall try to find out a bit more.

Sometimes, when handing over an completed instrument to its new owner, I catch myself wondering whether they have any idea of the time and trouble that has gone into making it. (Of course, it’s enjoyable time and trouble so I’m not complaining. Even so … ) But I suspect that instrument makers and woodworkers aren’t any better. When we buy wood we’re more likely to whinge about the price than to acknowledge the efforts and skills of the people who selected the log and converted it into sets of conveniently workable dimensions like those below.

1. There’s a brief biography of John Runk here.

2. Andy Fellows also sells wood at his on-line shop, Prime Timbers.

Having established, to my own satisfaction at least, that it would be asking for trouble to make a steel string guitar without a truss rod, the next question was which type to use and whether to arrange to get access to it at the top of the neck or the heel.

My friend Peter Barton, who makes beautiful steel string guitars in Yorkshire, recommended the Hotrod, which is a 2 way adjustable truss rod available from Stewart-MacDonald and looks like this.

But there were a couple of reasons why I had misgivings about this device. One was that it weighs over 100g and I thought it might make a small or medium sized instrument too heavy in the neck. The other was that it’s 11 mm deep and, although it would be easy to rout a deep enough slot to accommodate it, there wouldn’t be room to glue a fillet over it. The top of the slot would have to be covered by the bottom of the fingerboard and I worried that, when the rod was tightened up it might split the fingerboard or cause a bump.

To check, I made a model guitar neck out of a scrap of softwood, routed out a slot, installed the hotrod, glued on a pine ‘fingerboard’ and tightened up the trussrod as hard as I could.

It worked fine. My anxieties were unfounded: no splits or bulges in the fingerboard, even though it was made of nothing more substantial than cheap pine, and I could put a curve in the neck in either direction.

Still, there’s no getting away from that fact that it’s heavy.

An alternative, which is less than half the weight of a hotrod, is a simple tension rod. This what’s recommended by Jonathan Kinkead in his book Build your own Acoustic Guitar (ISBN 0-634-05463-5), where he gives instructions how to make and install it. I liked this idea because of its simplicity and light weight, and because it’s easy to arrange to adjust it through the soundhole, which means that there’s no need to excavate the headstock to provide access to the nut.

If you go for this solution, you have to find a way to anchor the rod at the top of the neck. Kinkead recommends a metal dowel tapped to receive the threaded end of the rod. I made one out of silver steel and repeated the earlier experiment.

It’s easy to install, although it’s important to judge the depth of the hole for the dowel accurately to avoid drilling right through the neck.

And it seemed to work OK too, although obviously it’s only able to bend the neck in one direction. However, when I took the fingerboard off, this is what I saw.

The fixing at the top end of the neck had been pulled out of its cavity and had begun to travel down the neck. Of course, this experimental neck is made of softwood and the problem might be less severe in a real mahogany neck. Even so, I thought there had to be a better solution.

It was the shape that was wrong. The cylindrical nut had acted a bit like a wedge. When I made a rectangular shaped nut out of mild steel, it stayed put.

As you can see, the first nut was unnecessarily wide. A narrower version worked just as well.

That’s what I decided to use in this guitar: a tension rod made of 5mm studding, anchored at the top of the neck with a square nut and adjusted through the soundhole. The nut at the top of the neck was silver soldered to the studding to prevent it moving during any adjustments at the lower end. Tension in the rod is controlled by turning a 5mm column hex nut bearing on a substantial washer at its lower end.

This arrangement worked well in the finished instrument and was more than powerful enough to keep the neck straight against the pull of the strings. Next time I make a steel string guitar, I shall be tempted to use 4mm studding instead of 5mm, which would mean even less weight in the neck.

Here are a few photographs of a recently completed steel string guitar. It’s based on a Martin ‘OO’ model but I’ve added, although that’s surely the wrong word, a venetian cutaway. The soundboard is Sitka spruce and the back and ribs are English walnut. I used holly for the bindings and tail stripe, and Rio rosewood for the bridge.





My friend, Dave Crispin, came to the workshop to try it out a few days ago and while he was playing I captured a few moments on an Edirol recorder.



This tool, designed and made by Brian Hart, is a purfling marker. As violin makers will know, when moved around the edge of a violin plate, it marks closely spaced parallel lines a few millimetres inside the perimeter to guide the subsequent cutting and chiselling-out of the narrow channel into which the purfling is laid.

If necessary, the distance between the lines can be altered by placing shims between the marking blades and there’s a screw mechanism to change the offset of the blades and allow precise adjustment of the distance of the purfling channel from the edge of the plate. A feature of the design is that the handle and centre of gravity are below the marking blades. I find that this makes it easier to use than the usual design of purfling marker, which has the handle on top.

Here’s the corner of a cello where the purfling was marked out using this tool.

But of course it only works where there’s an edge. It’s no use if you want to imitate the Brescian makers and create an elaborate pattern of the sort seen on the violin below.

(I’m grateful to Andrew Sutherland, a violin maker and restorer in Lincoln, for providing this photograph and information about the violin. It was made in Dresden, Germany around 1870. Andrew reckons that the ornamentation was done by a purfling specialist in the workshop where the instrument was made after it had been completed and varnished. There are more photographs here.)

 
 
 

A possible solution occurred to me when I read Jeff Peachey’s description of how he sharpened the tips of a pair of jeweller’s forceps to make a tool to cut thin strips of tissue for book restoration. I wondered if the same idea could be adapted to make a freehand purfling marker.

Here I’ve re-shaped the tips of a pair of stainless steel forceps using a slip stone to create bevels on the inner faces, and drilled and tapped a hole for a small machine screw.

With the addition of a fold of brass shim stock between the blades, the width of the gap between the tips of the forceps can be adjusted precisely.

It works fairly well and can be used either freehand or to scribe around a template. I found it best to make one pass with the marker and then use a knife to deepen the cuts rather than trying to use the forceps to cut deeply. Here are some first experiments.

A little decoration goes a long way and not everyone believes that violins are improved by a double line of purfling and stylised floral motifs. On the whole, I think this ornamentation works better on cellos and viols than it does on smaller instruments. Still, there are times when a flourish is desirable – the fingerboards and tail pieces of baroque violins, for example – so my new purfling marker will probably be used occasionally.

A comment on the previous post asked about setting the honing angle.

Here’s one way of doing it. Set a sliding bevel to the angle you’re after. (I chose 30°.) Then, after fitting the chisel into the mould, adjust the position of the mould in the honing jig, by eye, so that the longitudinal axis of the chisel runs parallel with the blade of the sliding bevel.

 

 

I glued a strip of wood across the underside of the mould so that it can be located in the honing jig at the same angle every time. And that’s it.

 

 

Eventually, I suppose, repeated honing will shorten the chisel and increase the angle of the secondary bevel. That will mean that it’s time to regrind the primary bevel and repeat this process to restore the angle of the secondary bevel.

A point I forgot to mention in the earlier post is that it’s worth creating a stop in the moulding at its upper end to prevent any tendency for the chisel to slide up while it’s being honed. Here you can see a stop formed by the lip that mirrors the indentation between the socket and the handle of the chisel.

 

A pair of chisels reground with left and right skewed edges is almost essential for cleaning out the sockets of lap dovetails. These chisels are useful for other tasks as well – tidying up the inside of the pegbox of a violin or cello, for example. I’ve got several pairs in different sizes and, although I don’t use them everyday, there are jobs where no other tool will do.

Actually, that isn’t quite true. A fishtail chisel makes a good substitute and, because it can work into both left and right pointing corners, you only need one tool rather than a pair. Last Summer, visiting Mark Bennett in his workshop in Yorkshire (see below) I saw him using one made by Lie-Nielsen. It was such an attractive looking tool that, even though I didn’t really need it, I couldn’t resist buying one to try.

After it arrived, I honed it, maintaining the 25° angle of the original grind. Perhaps it was my lack of skill – keeping such a small bevel flat on the stone wasn’t easy – but I never managed to get it properly sharp. What’s more, the edge that I did achieve didn’t stand up to use on hardwoods.

Of course, there’s an obvious solution to both these problems: create a secondary bevel at a slightly steeper angle. Indeed, Lie-Nielsen recommend exactly that in the leaflet that comes with the chisel.

However, I was reluctant to do this freehand because, although I was sure that it would work well enough the first few times, I knew that in the long run I’d be unable to maintain the same angle. This would mean that I’d end up with a rounded secondary bevel that would require more and more honing with each sharpening to get a decent edge. And, quite apart from the extra time this would take, it’s a bad idea to hone or grind a fishtail more than absolutely necessary. There isn’t much metal there in the first place and with each grinding the cutting edge gets progressive narrower. 

A honing jig would have solved the problem, except for the fact that I couldn’t make  the conical shape of the shaft of the tool  fit securely into any of the jigs in my workshop.

In the end, I got around this difficulty by casting a mould out of the sort of two-part wood filler that sets hard in about 30 minutes. I’ve written about this technique for holding awkwardly shaped object before (scroll down in the Tools and Jigs section of the website) so I won’t go into it in detail here. But briefly, you mix a generous quantity of the filler, spread it on a board (in this case a thin piece of wood of a size that would fit into an Eclipse honing jig), cover with a layer of cling film, and press the object you want to mould into it, holding it place with a weight or a clamp until the filler sets. Then, of course, you can take it out and get rid of the cling film.

I’m hoping that the photographs below will the idea clear:

And it worked – at least for one of the objectives. The edge on the chisel was keen enough to slice soft paper towel and to pare endgrain.

Whether it will achieve the second objective of minimising attrition of the blade with repeated sharpenings is another matter. Time will tell.

James Gordon, an engineer, materials scientist and naval architect, wrote two books that I highly recommend. I was about to write …to woodworkers but, actually, I highly recommend them to anyone who has the slightest interest in buildings, ships, aeroplanes or other artefacts of the ancient and modern world. My copies have been read and consulted so often that they’re falling apart. They are The New Science of Strong Materials or Why you don’t fall through the floor (first published in 1968, but still in print: ISBN-13: 978-0140135978) and Structures or Why things don’t fall down (first published in 1978 and also still in print: ISBN-13: 978-0140136289). Both are written for a non-expert readership and there’s very little algebra or mathematics. They’re fun too: Gordon writes clearly, wears his learning lightly and the text is spiced by his whimsical sense of humour.

The New Science of Strong Materials has many interesting things to say about the properties of wood and why it’s such a wonderful and versatile material. There’s stuff about how wood is able to cope with stress concentrations and limit crack propagation, about how glues work, the distribution of stress in a glued joint, and many other things of deep background interest, if not of immediate practical significance, to people who use timber.

The second book, Structures, is equally gripping. It explains how medieval masons got gothic cathedrals to stay standing, why blackbirds find it as much of a struggle to pull short worms out of a lawn as long ones, and the reason that eggs are easier to break from the inside than the outside. Of more direct relevance to woodworkers is its straightforward account of how beams work – which means that, if you’re thinking of making something like a bed or a bookcase, you can calculate whether the dimensions of the boards that you’re planning to use are up to the load they will have to bear, which is obviously useful in making sure that your structure is strong and stiff enough.

Slightly less obviously, it’s also helpful in giving you the confidence to pare down the amount of material that you might otherwise have used. A common fault of amateur woodworkers, it seems to me, is that when designing and making something small, they tend to use wood that is far thicker than it needs to be, which means that the finished object looks heavy and clumsy. Conversely, when making something large, they tend to use wood that is less thick than it should be, and the structure often ends up rickety and unstable.

Knowing a bit about beams might also be advantageous for guitar and violin makers. Here’s an example: take a strut or harmonic bar, rectangular in section, that you’re intending to glue onto the soundboard of a guitar. How is its stiffness related to its shape and its dimensions? What’s the best way to maximise stiffness while minimising weight?

Elementary beam theory tells us that, for a given length, stiffness is proportional to the width of the beam and to the cube of its depth. So if you double the width, the stiffness also doubles. On the other hand, doubling the depth, increases stiffness 8 times. If stiffness is what you’re after, it’s a lot more efficient to make the bar deeper than it is to make it wider.

This cubic relation between depth and stiffness could be something worth keeping in mind when planing down soundboard braces after they’ve been glued. If a brace is, say, 6 mm high to start with, planing it down by 1.5 mm to a height of 4.5mm will reduce its stiffness to less than a half of what it was originally. And shaping the braces to make them triangular or arched in cross section also reduces their stiffness considerably.

Mind you, like so many attempts to understand guitars from a scientific point of view, things rapidly get complicated. A structural engineer with whom I discussed the matter agreed with what I’ve just said about the depth of the beam being a powerful determinant of its stiffness. But he pointed out that where a beam is an integral part of a structure, the stiffening effect is much greater than you would guess from calculations that assume the beam is simply supported at its ends. This is certainly the case of guitars, where the braces are glued to the soundboard along their entire length and clearly count as an integral part of the soundboard structure. In such circumstances, he explained, the overall stiffening effect provided by multiple braces will be large and might well overwhelm the influence of the stiffness of any individual brace.

I thought that this was a very interesting idea and that it might begin to explain why so many different bracing systems work remarkably well. In Roy Courtnall’s book, Making Master Guitars, he give plans of soundboard strutting taken from guitars by a number of famous makers. Superficially they’re fairly similar, all being based on a fan-like pattern of 5, 7 or 9 struts. There are minor variations, of course. Some are slightly asymmetrical, some have bridge plates and closing bars and so on. But the  biggest differences lie in the dimensions of the braces. Courtnall shows a soundboard by Ignacio Fleta that has 9 fan struts and 2 closing bars which are 6mm in depth and an upper diagonal bar 15mm depth. By contrast, a soundboard of similar size by Santos Hernández has only 7 fan struts 3.5mm in depth and triangular in section. Applying simple beam theory would lead one to guess that Fleta’s bracing would add more than 10 times the stiffness that Hernández’s does. But perhaps that’s a misleading way to look at it. If one were able to measure or calculate the stiffness of the whole structure, by which I mean the soundboard with its bracing when attached to the ribs, the difference in stiffness between them might turn out to be much less.

It’s a question that might be tackled by finite element analysis and I’d be glad to hear from anyone who has tried. Some work along these lines has been done on modelling a steel string guitar, which at least shows that the approach is feasible.

In the meantime, without a proper theory, we’re stuck with the primitive method of trial and error. Below are some of the bracing patterns that I’ve experimented with. All produced decent sounding instruments but I’d be at a loss if I were asked which particular tonal characteristics were produced by each of the different patterns. It may be that William Cumpiano was right when he wrote (in his book, Guitarmaking, Tradition and Technology):

Specific elements of brace design, in and of themselves, are not all that important. One has only to look at the myriad designs employed on great guitars to recognise that there is no design secret that will unlock the door to world-class consistency.

All this means that I’ve been arguing in a circle. Perhaps the conclusion is that beam theory isn’t very useful to guitar makers after all. Still, if you take up the recommendation to get hold of Gordon’s books, the time you’ve spent reading this post won’t have been entirely wasted.

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