I undertook build #001 in 1987 when I was finishing college. I'm hoping to not wait another 27 years before starting build #003. :-)
I'm following plans laid out by J. S. Bogdanovich in his instructional book. I'm tweaking a few details (the topic of the next post), and just getting started.
Build #002 - Spruce/Rosewood Classical
Re: Build #002 - Spruce/Rosewood Classical
(Caution: this turned into a long-winded think-out-loud essay on the finer points of guitar design. TLDR: Experts disagree on some key geometries; rather than blindly pick an expert to model, I need to bring my own – albeit amateur – woodworking experience to bear in the decision.)
I’ve been making myself slightly crazy by diving into texts and plans written by a variety of classical guitar builders. While the general parameters of a classical guitar are fairly settled (scale length, length and width of body), there are lots and lots of details with the potential to significantly affect the quality of the sound and playability.
I’m a science guy, and I like mathematical models. It turns out that a few hard core acoustic scientists have tried to model the parameters that affect the quality of a guitar’s sound, but most professional builders have concluded that their information does not provide great guidance. In order to assess the effect of, say, the bracing pattern under the top, all other parameters (shape, thickness, overall manifold topology) have to be held constant. But if you go and then alter one of those other crucial parameters, the information gleaned about bracing patterns goes out the window. There are too many parameters to model.
When I have a statistical model with lots of parameters, I use computer algorithms to “hill climb” to an optimal solution for my problem. There might be hundreds of parameters to tweak – all the computer needs to know is that tweaking one parameter in a particular direction results in a better or worse fit to my desired outcome. The computer algorithm tries to efficiently simultaneously adjust everything at once in order to arrive at an optimal solution.
There are at least two reasons that approach won’t work for a builder. First, the sense of an “optimal” sound and playability is not static; every player wants something a little different in terms of sound color and string action. Some professionals have a quiver of instruments, each selected for playing a particular genre of music. So optimizing design parameters is not a one-off challenge; one has to understand how all of those might change depending on how one wants to color the sound. And the “color” of sound is itself a complicated quality to describe – another multi-parameter space.
The second problem is that incremental iterations toward an ideal sound happen one instrument build at a time. Even professionals working full time can at best turn out one instrument a week, and that’s with many of the processes automated. It takes years of iteration to gain an intuition of how altering a particular parameter set influences the final product.
Of course, I want to hit as close to a target of “good sound” as I can for guitar #002. One approach is to stand on the shoulders of giants – to pick a set of plans that have been evolved by an expert builder over decades, and use that as a model. After all, the expert has already gone through dozens if not hundreds of tweaks to his/her design in order to arrive at a good baseline. This is what I set out to do, basing my guitar on a design by J. S. Bogdanovich and published in his classical guitar making book. To triangulate against his designs, I’ve also been scrutinizing the text by Cumpiano and Natelson, as well as revisiting the guide I used for guitar #001, the classic text by Irving Sloane.
I’ve got an overall outline and bracing pattern (straight out of Bogdanovich), and many of the other parameters (top thickness, etc) are given in his book and are in accordance with other sources. There is just one place where all three texts disagree – somewhat radically – and it has major implications for the build. This is the geometry (or is it topology?) of the top and its relation to the neck angle.
(Edit: This is wrong - Sloane radiuses a transverse brace in the middle of the top with a caul) The simplest approach is that of Sloane – the top face of the neck (before the fingerboard is glued on) should be completely coplanar with the entire top, which itself is a simple plane. Now, it’s known that once the guitar is finished and the strings are tuned up, the tension on the top face (transmitted through the bridge) can tend to distort the top over time, pulling it up (bulging) behind the bridge and depressing it slightly in front (under the strings). If this distortion is severe it can affect the playability of the instrument, and then some replaceable pieces (namely, the nut and saddle) may have to be re-shaped.
There is one camp of builders that pre-stress the top by pressing it into a gentle curve and holding that shape with curved internal braces. Both Bogdanovich and Cumpiano & Natelson use curved tops. But now that I thought I had my parameter explosion under control, again I see subtle distinctions. Bogdanovich both curves the top and tilts the lower bout (the fat part of the body) back at an angle; essentially this compensates for the increased height of the bridge produced by the curve. Push the top out, tip it back, and in theory the bridge ends up in the same spot it would have been in an unstring, planar guitar. Cumpiano & Natelson curve the top but don’t perform any sort of tilting compensation. Then, just to make it really interesting, I’ve come across builders who curve the top but tilt the upper (smaller) bout of the guitar back, to change the overall angle at which the string intersects the top. This is the so-called elevated fingerboard design (this page by Howard Klepper describes his particular approach).
Here’s the last issue – some of these top geometries are much hard to execute than others for an amateur builder. Obviously, the flat plane is easiest. Next easiest would be the overall dome of Cumpiano & Natelson – the standard solution is to create a dished out work board that the top is pressed into when braces are glued on the underside. I’ve already taken the plunge and ordered two pre-made work boards with different degrees of curvature. My big problem is Bogdanovich’s approach – the combination of a curve and a tilt means that one has to (pretty laboriously) hand-shape some of the work board, and there’s an aspect of his neck angle that still doesn’t make 100% sense to me.
And that’s the final rub, my lightbulb moment – whatever I choose for a plan going forward, it has to make sense to me as a builder. I clearly don’t have all the answers, but I’m not a completely blank slate, either. To my eye, there are just too many tweaks that Bogdanovich has to make to his components (shaving a bit under the fingerboard, etc.). So I’m inclined to either go with the general curve of Cumpiano & Natelson (not compounded with a tilt), or punt entirely and use a purely planar design. Maybe someday I’ll come to understand the advantages of Bogdanovich’s lower bout tilt (which is exactly the opposite of the elevated fingerboard approach used by Klepper and others).
At this point I’ve reduced my parameter space to a single binary choice – planar or generally curved. I think I can live with that and move forward, holding the other parameters constant.
I’ve been making myself slightly crazy by diving into texts and plans written by a variety of classical guitar builders. While the general parameters of a classical guitar are fairly settled (scale length, length and width of body), there are lots and lots of details with the potential to significantly affect the quality of the sound and playability.
I’m a science guy, and I like mathematical models. It turns out that a few hard core acoustic scientists have tried to model the parameters that affect the quality of a guitar’s sound, but most professional builders have concluded that their information does not provide great guidance. In order to assess the effect of, say, the bracing pattern under the top, all other parameters (shape, thickness, overall manifold topology) have to be held constant. But if you go and then alter one of those other crucial parameters, the information gleaned about bracing patterns goes out the window. There are too many parameters to model.
When I have a statistical model with lots of parameters, I use computer algorithms to “hill climb” to an optimal solution for my problem. There might be hundreds of parameters to tweak – all the computer needs to know is that tweaking one parameter in a particular direction results in a better or worse fit to my desired outcome. The computer algorithm tries to efficiently simultaneously adjust everything at once in order to arrive at an optimal solution.
There are at least two reasons that approach won’t work for a builder. First, the sense of an “optimal” sound and playability is not static; every player wants something a little different in terms of sound color and string action. Some professionals have a quiver of instruments, each selected for playing a particular genre of music. So optimizing design parameters is not a one-off challenge; one has to understand how all of those might change depending on how one wants to color the sound. And the “color” of sound is itself a complicated quality to describe – another multi-parameter space.
The second problem is that incremental iterations toward an ideal sound happen one instrument build at a time. Even professionals working full time can at best turn out one instrument a week, and that’s with many of the processes automated. It takes years of iteration to gain an intuition of how altering a particular parameter set influences the final product.
Of course, I want to hit as close to a target of “good sound” as I can for guitar #002. One approach is to stand on the shoulders of giants – to pick a set of plans that have been evolved by an expert builder over decades, and use that as a model. After all, the expert has already gone through dozens if not hundreds of tweaks to his/her design in order to arrive at a good baseline. This is what I set out to do, basing my guitar on a design by J. S. Bogdanovich and published in his classical guitar making book. To triangulate against his designs, I’ve also been scrutinizing the text by Cumpiano and Natelson, as well as revisiting the guide I used for guitar #001, the classic text by Irving Sloane.
I’ve got an overall outline and bracing pattern (straight out of Bogdanovich), and many of the other parameters (top thickness, etc) are given in his book and are in accordance with other sources. There is just one place where all three texts disagree – somewhat radically – and it has major implications for the build. This is the geometry (or is it topology?) of the top and its relation to the neck angle.
(Edit: This is wrong - Sloane radiuses a transverse brace in the middle of the top with a caul) The simplest approach is that of Sloane – the top face of the neck (before the fingerboard is glued on) should be completely coplanar with the entire top, which itself is a simple plane. Now, it’s known that once the guitar is finished and the strings are tuned up, the tension on the top face (transmitted through the bridge) can tend to distort the top over time, pulling it up (bulging) behind the bridge and depressing it slightly in front (under the strings). If this distortion is severe it can affect the playability of the instrument, and then some replaceable pieces (namely, the nut and saddle) may have to be re-shaped.
There is one camp of builders that pre-stress the top by pressing it into a gentle curve and holding that shape with curved internal braces. Both Bogdanovich and Cumpiano & Natelson use curved tops. But now that I thought I had my parameter explosion under control, again I see subtle distinctions. Bogdanovich both curves the top and tilts the lower bout (the fat part of the body) back at an angle; essentially this compensates for the increased height of the bridge produced by the curve. Push the top out, tip it back, and in theory the bridge ends up in the same spot it would have been in an unstring, planar guitar. Cumpiano & Natelson curve the top but don’t perform any sort of tilting compensation. Then, just to make it really interesting, I’ve come across builders who curve the top but tilt the upper (smaller) bout of the guitar back, to change the overall angle at which the string intersects the top. This is the so-called elevated fingerboard design (this page by Howard Klepper describes his particular approach).
Here’s the last issue – some of these top geometries are much hard to execute than others for an amateur builder. Obviously, the flat plane is easiest. Next easiest would be the overall dome of Cumpiano & Natelson – the standard solution is to create a dished out work board that the top is pressed into when braces are glued on the underside. I’ve already taken the plunge and ordered two pre-made work boards with different degrees of curvature. My big problem is Bogdanovich’s approach – the combination of a curve and a tilt means that one has to (pretty laboriously) hand-shape some of the work board, and there’s an aspect of his neck angle that still doesn’t make 100% sense to me.
And that’s the final rub, my lightbulb moment – whatever I choose for a plan going forward, it has to make sense to me as a builder. I clearly don’t have all the answers, but I’m not a completely blank slate, either. To my eye, there are just too many tweaks that Bogdanovich has to make to his components (shaving a bit under the fingerboard, etc.). So I’m inclined to either go with the general curve of Cumpiano & Natelson (not compounded with a tilt), or punt entirely and use a purely planar design. Maybe someday I’ll come to understand the advantages of Bogdanovich’s lower bout tilt (which is exactly the opposite of the elevated fingerboard approach used by Klepper and others).
At this point I’ve reduced my parameter space to a single binary choice – planar or generally curved. I think I can live with that and move forward, holding the other parameters constant.
Last edited by Larry G on Sat Apr 05, 2014 11:36 pm, edited 1 time in total.
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John Parchem
- Posts: 2749
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Re: Build #002 - Spruce/Rosewood Classical
I also have read all of the books you have and went through many of the same thoughts. My goal on my 1st through my current guitar has been to improve my craft and produce good guitars. I have no real idea even what I would want as an optimal sound.
To your thoughts on geometry, my final goal for a classical guitar is to have the bass strings 11 mm off the sound board with the action set to 3 mm at the 12th fret. I do not believe any of the methods you listed to set the geometry will be a big factor in the sound of the instrument. I have tried two methods to achieve this set up: 1) Flat neck angle with a tapered fret board built on flat solera with a dished out lower bout. 2) I used that same solera and planed down the neck portion of the solera at an angle such the nut will be 2 mm higher than the plane of the top.
Both of these methods are about the same amount of work to achieve the same geometry. The first method required me to plane a new plane into the bottom of a slotted fret board. The angle of the plane was from the treble side nut to the bottom of the fret board on the base side. What I wanted to achieve was setting the overall fret board angle nut to saddle and also thinning the bass side a bit more to give and extra mm or so of action on the base side. Sounds more complicated than it is.
The second method gave me the neck angle nut to saddle. I would still thin the bass side of the fret board a mm for increased action on the bass side. Given that I have a neck angle and as I build my top on a solera I need to sand a bottom of the fret board from the 12th fret on to so that the fret board fits the top.
Once the fret board was glued on I would check the geometry using a straight edge and use a flat bar sanding block to fine tune it.
Both of these methods worked out fine. As you noted there are other ways to achieve the same geometry.
If you are working from plans for any of the good reference classical guitars I think that the acoustic quality of the top, the thicknessing of the top based on its characteristics and the optimization of the braces including height of the braces in that order are where to focus to achieve a good sound.
I would chose a design\build style the you feel the most comfortable implementing.
To your thoughts on geometry, my final goal for a classical guitar is to have the bass strings 11 mm off the sound board with the action set to 3 mm at the 12th fret. I do not believe any of the methods you listed to set the geometry will be a big factor in the sound of the instrument. I have tried two methods to achieve this set up: 1) Flat neck angle with a tapered fret board built on flat solera with a dished out lower bout. 2) I used that same solera and planed down the neck portion of the solera at an angle such the nut will be 2 mm higher than the plane of the top.
Both of these methods are about the same amount of work to achieve the same geometry. The first method required me to plane a new plane into the bottom of a slotted fret board. The angle of the plane was from the treble side nut to the bottom of the fret board on the base side. What I wanted to achieve was setting the overall fret board angle nut to saddle and also thinning the bass side a bit more to give and extra mm or so of action on the base side. Sounds more complicated than it is.
The second method gave me the neck angle nut to saddle. I would still thin the bass side of the fret board a mm for increased action on the bass side. Given that I have a neck angle and as I build my top on a solera I need to sand a bottom of the fret board from the 12th fret on to so that the fret board fits the top.
Once the fret board was glued on I would check the geometry using a straight edge and use a flat bar sanding block to fine tune it.
Both of these methods worked out fine. As you noted there are other ways to achieve the same geometry.
If you are working from plans for any of the good reference classical guitars I think that the acoustic quality of the top, the thicknessing of the top based on its characteristics and the optimization of the braces including height of the braces in that order are where to focus to achieve a good sound.
I would chose a design\build style the you feel the most comfortable implementing.
Re: Build #002 - Spruce/Rosewood Classical
I'm starting to keep a running photo log (with minimal commentary) on Imgur (
Yesterday I had my first setback in neck construction. I'd pretty much finished the headstock, except when I first drilled the tuner holes I used a general purpose centering doweling jig with guides for standard sizes like 1/4, 5/16, etc. 3/8" was the largest bore, so use used that, thinking I'd enlarge it to 13/32" later. So I trilled the holes for the tuning machines, then routed out the slots, and everything was looking pretty good. Then, after acquiring a 13/32" drill and building myself a proper jig to drill 13/32" holes at the correct spacing, I used that to enlarge the holes.
I forgot a cardinal rule of wood boring - make sure you've got the back side of your workpiece supported or you'll get tear-out. Even shaving off an additional 1/32" of wood was enough to chip out the mahogany on the inside of the tuning slots. :-(
Then, I also mis-calculated a band saw angle setup as I was rough cutting the geometry for the foot (the part inside the body). Nobody will ever see the asymmetry that resulted (I caught it in time and was able to fix the mistake, but there's still a small chunk taken out of one side of the foot under the top), but still, I should have caught that earlier.
So now I'm thinking this will become my "practice" neck, and I'll be building a second one (correctly) right behind it. I'm about to approach carving the heel, and I'm sure there are place where I'll screw up or need to at least risk screwing up before getting it right. I want to be fresh off a practice piece before doing it for real. Mahogany is relatively cheap, so I don't begrudge sacrificing this wood.
I'll post photos of the goofs soon...
Yesterday I had my first setback in neck construction. I'd pretty much finished the headstock, except when I first drilled the tuner holes I used a general purpose centering doweling jig with guides for standard sizes like 1/4, 5/16, etc. 3/8" was the largest bore, so use used that, thinking I'd enlarge it to 13/32" later. So I trilled the holes for the tuning machines, then routed out the slots, and everything was looking pretty good. Then, after acquiring a 13/32" drill and building myself a proper jig to drill 13/32" holes at the correct spacing, I used that to enlarge the holes.
I forgot a cardinal rule of wood boring - make sure you've got the back side of your workpiece supported or you'll get tear-out. Even shaving off an additional 1/32" of wood was enough to chip out the mahogany on the inside of the tuning slots. :-(
Then, I also mis-calculated a band saw angle setup as I was rough cutting the geometry for the foot (the part inside the body). Nobody will ever see the asymmetry that resulted (I caught it in time and was able to fix the mistake, but there's still a small chunk taken out of one side of the foot under the top), but still, I should have caught that earlier.
So now I'm thinking this will become my "practice" neck, and I'll be building a second one (correctly) right behind it. I'm about to approach carving the heel, and I'm sure there are place where I'll screw up or need to at least risk screwing up before getting it right. I want to be fresh off a practice piece before doing it for real. Mahogany is relatively cheap, so I don't begrudge sacrificing this wood.
I'll post photos of the goofs soon...
Re: Build #002 - Spruce/Rosewood Classical
After deciding I couldn't live with the chip-out on the first neck, I started a second one. I still made a few small mistakes in carving the headstock, but I'm pretty confident that with some careful chisel and file work I can make the headstock look pretty.
At first I'd decided to follow Bogdanovich's text pretty closely, but I'm really having second thoughts about a couple of design elements. The first is using a Spanish heel for the neck to body joint. The majority opinion from experienced luthiers is that bolt-on is the way to go. What's swinging me in that direction in particular is that I don't yet have an intuition for how neck set is going to affect action and tone. Bogdanovich tips the neck forward slightly (so that the plane of the fingerboard dives into the top), and then tapers under the fingerboard to lie flush with the upper bout. Others keep the neck coplanar with the upper bout. Some steel string builders even build a bit of back-set in, if I understand correctly, to compensate for the string tension. With a bolt-on I have at least an option of adjusting neck set before committing. With a Spanish heel I have to just hope everything works out the way his plans say they will.
I've also decided to hand-bend solid sides on a bending pipe rather than use a mold and laminated sides. This is purely for the experience of hand-bending. After practicing on some scraps of rosewood I've had laying around, I finally bent the sides today, and they came out fairly decently, generally no more than 1/16" off the template outline. I still have a little touch-up to do before final assembly, and in particular I want to make sure all curves are fair (no "lumpiness" of a sharp bend followed by a flat spot). Depending on how everything turns out I may continue with hand bending in the future or switch to laminations and molds (I like the idea of lamination for its stiffness and ease of bending without a bending machine).
So I've set the aside while I ponder the wisdom of trying a bolt-on. The sides will need a little touch up, but they're set aside too. I just joined and glued the top plates tonight, and will start on thicknessing and inlaying the (pre-bought) rosette.
At first I'd decided to follow Bogdanovich's text pretty closely, but I'm really having second thoughts about a couple of design elements. The first is using a Spanish heel for the neck to body joint. The majority opinion from experienced luthiers is that bolt-on is the way to go. What's swinging me in that direction in particular is that I don't yet have an intuition for how neck set is going to affect action and tone. Bogdanovich tips the neck forward slightly (so that the plane of the fingerboard dives into the top), and then tapers under the fingerboard to lie flush with the upper bout. Others keep the neck coplanar with the upper bout. Some steel string builders even build a bit of back-set in, if I understand correctly, to compensate for the string tension. With a bolt-on I have at least an option of adjusting neck set before committing. With a Spanish heel I have to just hope everything works out the way his plans say they will.
I've also decided to hand-bend solid sides on a bending pipe rather than use a mold and laminated sides. This is purely for the experience of hand-bending. After practicing on some scraps of rosewood I've had laying around, I finally bent the sides today, and they came out fairly decently, generally no more than 1/16" off the template outline. I still have a little touch-up to do before final assembly, and in particular I want to make sure all curves are fair (no "lumpiness" of a sharp bend followed by a flat spot). Depending on how everything turns out I may continue with hand bending in the future or switch to laminations and molds (I like the idea of lamination for its stiffness and ease of bending without a bending machine).
So I've set the aside while I ponder the wisdom of trying a bolt-on. The sides will need a little touch up, but they're set aside too. I just joined and glued the top plates tonight, and will start on thicknessing and inlaying the (pre-bought) rosette.
Re: Build #002 - Spruce/Rosewood Classical
All but one of the classicals I have made have bolt on necks -- practicality, preference versus tradition nothing more. Also, put a truss rod in it too -- you will not regret that either.
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John Parchem
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Re: Build #002 - Spruce/Rosewood Classical
Lot of classical builders use a bolt on neck, not a bad way to go. I would consider a neck block that looks more like a classical with the longer slipper in the back as the classical bracing does not really have any structural longitudinal bracing. I think the easiest option is to build the neck flat and put a slight longitudinal taper in the bottom of the fret board. The difference in angle from a steel string is to adjust for a higher action (about 1 mm higher at the 12th fret) and a lower height over the top at the saddle for the classical sound (11 mm vs around 14mm for a SS). None of my classical necks really move much under tension. Truss rod is a good idea as well.