MY SOUNDBOARD LOOKS LIKE A POTATO CHIP!
SIDE BENDING TIPS AND OPTIONS
WHAT COLOR CHEESE IS THE MOON MADE OF?
WHY CAN'T AN ACOUSTIC BE MORE LIKE
IS IT "ALLOWABLE "TO RADIUS A
KEEPING THE HEADBLOCK ANGLE FIXED IS
SCALE LENGTH CONSIDERATIONS
LOWERING THE ACTION BY SHAVING THE BRIDGE
LACQUER FINISH DRIED SOFT!
WHY IS MY GUITAR DEAD IN PLACES?
CAN THIS YAMAHA BE SAVED?
WHAT DO I DO NOW, UNCLE BILL?
IS THERE AN EASIER WAY TO THIN THE
FRETBOARD SURFACE GEOMETRY: RUMINATIONS
THE BRIDGE PIN'S CONTRIBUTION TO ACOUSTIC
OAK FOR GUITARS?
LEAVE NO VAPOR BARRIER UNDER THE BRIDGE!
HOW WOULD IT SOUND IF I...?
|My soundboards looks like a potato chip...
© William R. Cumpiano 2003, All Rights Reserved
I have been building a guitar over
the past several months using your book as my guide. Everything seemed to be going very
well, but when i left the top plate sitting in my garage on my workbench for about a week
or so it warped. The top was completely finished with rosette and all bracing in place and
shaped. If I hold a straight edge across both the lower and upper bout i have a gap in the
center of about 3/16 inch. It seems as if the top plate has shrunk and force the bracing
to bow. Is there a way to fix this or do i need to start over and how do I avoid this in
Sorry you have a problem.
You must have skipped page 157, the discussion titled "humidity". The reason for
your current dilemma is stated plainly there.
Without a climate-controlled room (air conditioner, room humidifier, room dehumidifier,
all set to 70 degrees and 40-45% humidity all the time), you are at natures fickle
mercy. I'm afraid there is no way of undoing nature's work--other than:
1- Carefully chisel off all the major curved braces and upper transversal face graft.
2- Prepare your new top braces but don't glue them on. Proceed to side bending, and
fabricate and gather all the soundbox parts before actually assembling them together. You
can take your time making them in an uncontrolled humidity environment.
3- Reserve a long weekend, or a time that you can devote a full three or four days full
time to the guitar. Oh, and that 3-4 day period CAN'T fall on a rainy period or the
hottest time of the year, i.e., during any extreme weather period.
4- Assemble the entire soundbox according to instructions in the book over this collapsed
3-4 day time period. Once the soundbox is built, you shouldn't have to worry about
humidity any more.
That's how good guitars are built. I'm
sorry it's so much trouble...
tips and options
>Do you bend all your sides with a hot pipe? Woods such
as maple seem to be very difficult to bend without damaging the wood. What do you think
about the side bending machines such as the Fox side bending machine heated with light
bulbs? I have heard there is a small amount of spring back, I have never built a guitar
using a mold, do you think the spring back would be a problem using the free standing
method described in your book. I have been thinking about adding one of these machines to
my shop, and I would really appreciate any information you can send me. Thanks.
I have four or five side molds for the more common shapes that I build, and I use a
Luthier's Mercantile Side Bending heating blanket (with a rheostat) laid on top of them. I
clamp a shaped shoe down on the side slat at the waist and clamp the ends to the mold. It
works rather well. Ive seen others use the Fox light bulb bending machine to good
The trick is to let the sides "cook" for half a minute before shutting the heat
off, and then leaving them to cool and dry thoroughly for two to four hours, if not
overnight, before unclamping them--which reduces spring back in most woods (there is
virtually no springback if you let them sit clamped overnight to fully cool and dry). I
touch up the residual spring-back on the hot pipe just before assembling the sides to the
For the unusual, or one-of-a kind shapes, I use my bending iron. For this I avail myself
of my many years of experience to get them right with a minimum of damage or scorching. It
takes practice...what more can I say? You get a feel for when the wood is getting too hot,
or when it is about to break. Its easier to demonstrate than to describe. More like
But the mold and blanket, or light bulb system is pretty foolproof and an excellent option
to people who feel life is too short to learn hot pipe side bending... and willing to make
just two or three different size and shape guitars, only the shapes that you have a mold
Here's some useful tips:
* Bending at the right thickness is key here: the difference in bending ease between
.080" and 090" is vast.
* Your chances of success improve if you know what the temperature is, and can set it with
some accuracy. I have a digital thermometer (pyrometer) and don't start to bend below 250
degrees F. Above 300 degrees darkening begins and at about 325 to 350 scorching begins.
Clearly the wood can bear more heat moving over a hot pipe than sitting immobile over a
heating blanket. So contact time is a factor.
Maple stains easily on the hot pipe AND on the molds. The main thing here is to clean the
pipe of old dark resins from bending other woods and use strictly distilled water. The
minerals in tap water boil deep stains into the pale wood. But Maple, as all the temperate
climate hardwoods are especially easy to bend actually. It's the tropical hardwoods that
are difficult, especially mahogany (it tends to fold at tight bends instead of bend) and
some of the extremely dense rosewood hybrid species (which spring back in major ways and
you have to bend and rebend three or four times).
Yes, its a challenge. If it were easy, you'd probably not want to do it, right?
>When I use my bending iron to bend the tight radius in the middle of each side I
get a somewhat splitting almost like a pulling or cracking just about in the middle of the
bend. What am I doing wrong? Is the iron to hot or is the wood (mahogany) not thin enough
(.008-.009). I am using a pipe that is approx. the same radius.
"Somewhat splitting, almost like a pulling or cracking"... ah, yes, mahogany...
If it's creating what looks like a wandering cross-grain split, right at the stress point,
it's the tissue collapsing. For any side material to bend, one face has to stretch and the
other has to compress. Mahogany can stretch far more than it can compress. In this way,
mahogany is in the bad to bend category as are most tropical hardwoods
(Northern hardwoods, like beech or birch or maple are in the good to bend
category). The tissue is folding into itself right at the spot where its being
forced to compress. If you're lucky, the lines can be scraped away if they're not too
deep. Otherwise...you'll have to throw it away and start again. Next time change your
technique by one or more of the following:
* Change the waist template contour to a less radical bend. Big help. Why do you think
Martin loved Dreadnaughts so much?
* Don't soak so long; or don't soak at all and just spritz it generously as you're
bending. Overwetted mahogany collapses easier.
* Thin the blank further just in region of the bend. There's a world of difference between
.080 and .090. Tight waisted bends are very difficult at .090, far easier at .080. If
its a deep body guitar, don't go much under .085, or your sides will end up looking
like wavy gravy. If you don't have the capacity to gauge the wood that closely,
well...develop it or live with the results.
color cheese is the moon made of?
>Which bridge pad material allows for a brighter tone [on a steel string
guitar]? I was doing a web search in the hopes of finding out what different guitar
builders and repairmen's opinions were on what wood allows for a brighter sound in a
spruce top dreadnought guitar for use in the bridge pad; rosewood or maple.
Your query is phrased not as a question but as an assertion. It asserts that the bridge
pad specie determines the brightness or darkness of the tone. So now, which species makes
the guitar brighter?
Your question is not exceptional. I get these all the time. They ask me to clarify some
detail or other of an assumed, shaky premise. What color cheese, exactly, is the moon made
Forgive me: I'm not trying to be a wise-ass. Youre just asking the wrong guy. You
should really ask the guy who convinced you that the bridge pad affects the guitars
brightness. No doubt hell lead you even further astray.
As for me, its a moot point. Im content to choose species hard enough to keep
the ball ends of the strings from driving their way through the soundboard. As for its
effect on the tone, I can only comment that there is just no way to ascertain
how changing any single element on a guitar is going to change its sound, when a
guitar is composed of hundreds of interacting and interconnected elementssome of
which you can consciously make decisions about, and others that you cant. This
particular builder can't tell you--or if he could, can't describe to you--the effect on
the whole of changing just one of those decisions.
The sound of a guitar is the sum total of hundreds of decisions that the builder has
madeand a series of givens the builder must simply deal with and accept. Some of
these givens are the traditional form of the guitar. The bridge patch is
there, traditionally, not to change the tone, but for more practical reasons. Attributing
an after-the-fact precise and predictable tonal function to it is one of those shaky
The other problem is in describing sound with words: I really can't tell what sound you're
hearing in your head when you ask me about a "brighter" sound; or a
"warmer" sound. Or a darker sound. Or a "clearer" sound.
Yes, my answer is unsatisfying. I could just tell you that rosewood bridge patches
allow for a brighter sound. That answer would be more
satisfactory, no doubt. But then you would be getting your information from a faker or a
cant an acoustic guitar be more like an electric?
>It seems to me that electric guitars have much lower action AND less string
tension than acoustic steel string guitars. Is this just my imagination or is it just due
to the fact that I have never played an expensive or custom acoustic guitar that achieves
low action without fret buzz?
At a given pitch a thicker gauge string produces more acoustic output when plucked than a
thinner gauge string. It also feels stiffer because a thicker string is less elastic than
a thinner string. Thinner gauge strings are usually put on electrics because you don't
need the acoustic output. You just turn up the amp if you want more volume. So electrics
feel softer to play. And when you play an acoustic, you have to pluck harder because you
want to hear it. On an electric, you don't pluck as hard because you can hear it by just
turning up the amp. If a player (acoustic or electric) usually plucks softly, the action
can be set lower. If his technique is to play harder, you have to raise the action, or
hell complain about buzzing. If an electric player plucked his strings as hard as an
acoustic player has to, and his action is set very low, it would buzz. You can't expect to
set the action super low and then pluck hard on it, and not get any buzzing.
Lower action with less buzzing can be achieved on both electrics and acoustics if the
fretwork set-up is expertly done. Again, in either case, you can force a buzz by playing
hard enough to drive the string to hit the fret. An expert player can play more vigorously
with low action because he/she knows how to strike the string in a way that buzzing is
reduced. So technique is a big factor here also. Indeed there are many other factors, such
as the effect of the scale length and the resonances in individual guitars that can make a
string's vibration increase (the string sets the guitar in motion. But remember: the
guitar is the platform for the strings. So it feeds energy back to the string. Acoustic
guitars are made to be as compliant to vibration as possible, electric guitars are not. So
the feedback effect is exacerbated on acousticsgenerally requiring higher action
than on electrics). You have to look at the individual case.
And yes, a more skilled makers/technicians can optimize action by bring their experience
to bear. They can indeed, lower the threshold at which a string starts buzz at lower
action settings on any given guitar by improving the guitars fretwork and set
up...and instructing the players how their technique can result in cleaner playing.
allowable to radius a classic fingerboard?
Thanks for writing your book and providing the informative website. I am a new
builder. Classical fingerboards are typically flat (as I have found in my research to
date). Is it blasphemous to put a radius on a classical fingerboard? Are professional
builders selling classical guitars to students/guitarists with radiused fingerboards?
Is this too great a break from tradition?
Not too great. Classical making has become far less hide-bound than it used to be, and if
a slight radius provides greater comfort for the less expert musician, go for it. We
actually radiused a boardto a dramatic degreeon a classical belonging to a
recitalist that had developed a condition in his barring finger that prevented him from
straightening it (trigger finger its called). We actually curved the
board to precisely match the contour of his locked barring finger.
He's back in business, and by the way, it turns out to be fabulously comfortable for
non-ailing guitarists who don't practice a lot (like me), although the required arch on
the saddle and the resulting curve of the string array takes some getting used to for the
headblock angle fixed is crucial!
I'm a custom furniture maker trying my first guitar and I have question, if you have
time to reply. I understand that the curved upper face brace should impart enough dome to
the soundboard so the end of the fingerboard will sit correctly when the neck is backset.
But what about the headblock? If it's top is flat, then the first two inches of the top
will be flat. Should the front of the headblock (and the front of the upper bout) be
shaved down slightly? I don't know if affects anything, but I'm building in an outside
mold rather than on a workboard.
PS: your book is dangerous. I'm having a hard time working on the paying jobs in my shop
since I got it.
Congratulations--you're the first beginner that has successfully visualized that esoteric
spatial relationship. It has been missed by something like a thousand inquirers since the
book was published in 1985.
Well, what actually happens is that the rise in the top (towards the soundhole) causes the
headblock (and attached sides) to rotate minutely. This can happen because there's a bit
of flex in the system. And that's okay. The result is that the outer face of the headblock
will not end up strictly perpendicular to the workboard, but tipped back by a degree or
so. It's okay because the neck itself has to be tipped back by a degree or so, and that
should preserve the perpendicularity that is required in the region of headblock, which
should approximately match the perpendicularity that exists between the heel bearing
surface and the fingerboard tongue.
But problems can occur if you inadvertently increase the headblock angle during the
assembly process. That small angle offset should remain after the back is glued on,
because its the event which locks the headblock's orientation in place forever. Clearly,
if the headblock has been forced back too far, it will force a slight hump in the top
where the fingerboard will be glued. If the headblock ends up perpendicular or worse,
tipped FORWARD, you will end up with a hollow in the area above the soundhole.
In what ways, then can the headblock be forced to end up in an improper angle? If you are
using the workboard shim, you have to be careful when you add the additional shims under
the upper transversal face brace that, when you clamp the guitar down with the workboard
shoe by tightening down the wingnut (that is drilled through the soundhole), that you do
not rack the headblock back. I just start with an oversized shim and sand it thinner
progressively until I can snug the wing nut down without watching it pull back on the
Since I announced in my website that I was recommending a barrel bolt neck attachment
system over the pinned mortise and tenon system (were you aware of that? Details are on my
website.) I can now take advantage of the large bolt holes that now appear on the back
wall of the headblock. They allows the headblock to be screwed and thus fixed securely to
a vertical extension to the workboard shoe. through the assembly process. The trick is to
trim the shoe extension to the same angle as the headblock tip-back. A little trial and
error will get it right. After the back is glued on on, remove the screw that tightens the
headblock to the shoe, and after unscrewing the shoe from the workboard, the shoe can be
worked out through the soundhole.
>Can you tell me where I can get some information on short scale (630 to 640mm)
classical guitar construction? I would like to have one built but would like to learn
first what should be considered in terms of body size, bridge placement, neck size, string
distance etc in order to get an instrument with good tone and volume. I have small hands
and would like a guitar that is easier to play but still sounds good.
The information you seek is rather specialized, I doubt that there is much published on
specifically short scale guitars. But I can venture the following comments: Shorter scales
certainly facilitate long reaches, as would fingerboards that are less wide and necks that
are less thick. The last two have little effect on the guitar's performance (much more on
the guitarists) but there are serious consequences to shortening or lengthening the
scale on a guitar; some would say dramatic. Some of the consequences can be mitigated, or
balanced by changes in the soundbox design, but not all.
A change in string tension is the greatest overarching consequence. You have to wind a
longer string tighter than a shorter string to have them both reach the same pitch. Thus,
a shorter scale guitar has its strings somewhat looser than a longer (even when both are
tuned to the same open-string notes). The amount of energy the strings are applying to the
soundboard is thus less, and not just that: the rise and fall of the plucked note's sound
is rounder (as contrasting to the "snap" of a long scale string); and the
harmonic content of the shorter string's signal is proportionately richer in higher
frequency components--and viceversa. So we may say that long scale guitars have a more
"baritone" quality and short scale guitars have a more "tenor" quality
to them. So there is variation in the sound character--proportionately--among shorter and
longer scale guitars.
There is some difference in opinion about loudness and projection difference. Where one
would expect that the greater power inherent in greater tension would yield a larger tone
with more projection, in fact a shorter scale guitar typically produces its power in the
higher frequencies, in the ranges where the human ear is more sensitive, so many small
guitars seem disproportionately loud for their size and their voice seems more penetrating
or "piercing" than a deeper-voiced instrument.
The "quality" of the sound (rather than its character or relative loudness), I
feel safe in declaring, has little to do with the scale length or neck contour, but more
to do with the quality of materials and appropriate design and execution of the soundbox.
That of course, depends on the skill and experience of the luthier, who should be able to
make a beautiful sounding instrument, from a 12" scale guitarrillo to a 30"
scale guitarron, and all shades in between.
action by shaving the bridge
>Could you please comment on this alternative method to an acoustic guitar neck
reset? I hear quite a few repairmen talk about thinning and recountouring the bridge and
ramping the string holes so that the saddle can be lowered even more and proper string
angles retained. I think that, while this repair may solve the problem temporarily, a neck
reset will be required anyway in a few years time, and then the bridge will have to be
replaced, too. Maybe this technique will give some life to cheaper instruments
(considering the high cost of a neck reset). What do you think?
There is no doubt that some repairs are appropriate for expensive and valuable instruments
that aren't appropriate for less expensive instruments, and vice-versa. But since there
are so many factors involved, sometimes there is a difference of opinion about which
repairs are appropriate in each specific case. So it is difficult to assert a rule that
covers every possible case.
Thinning and re-contouring the bridge is appropriate for inexpensive instruments if it
will return it to easy action at a low cost. But even if the instrument is expensive,
thinning and re-contouring the bridge may be also appropriate, but only if, in the
judgment of an expert luthier, it is excessively massive to start with, and if the process
may actually improve the instrument's acoustic response. Thinning and re-contouring is
never appropriate for a vintage or historic instrument.
Neck resetting may be economically AND physically impossible on inexpensive instruments.
There are even some experts who maintain that neck resets are bad even for good
instruments because of the potential stress and risks involved. They maintain that bridge
thinning and re-contouring is the least stressful solution, thus the most responsible on a
valuable guitar in every case (Are you out there, Matty?). But this opinion is rare,
although there can conceivably be certain specific instances where they are indeed
The problem ultimately with thinning and re-contouring is that if the instrument is built
in such a way that it's distortion is progressive (which is the case with many, but not
all, steel-string instruments) there will inevitably come a time when the bridge cannot be
further thinned. A neck reset is then the only solution, in which case, yes, the bridge
should be replaced also. On an inexpensive instrument, the most economical solution may be
to "put it out to pasture."
>I have finally after a few delays finished my guitar with lacquer as suggested in
your book. Two coats sprayed on, wait 24 hours, wet sand, two more coats, wait 48 hours
(actually more) then wet sand. The final wet sand was with 600 and then 1200 grit wet
paper.After sanding I buffed the surface with an automotive compound designed for lacquer.
The finish buffed out beautifully! However, here is my problem. When I lay the guitar down
on a surface, such as a cloth, towel, etc (never a hard surface) the cloth will leave
light impressions in the finish after a couple of hours or so. The finish feels solid so I
am sure it is dry. I did notice that his did not occur after sanding and prior to buffing.
Do you have any advice on this? I am at a loss. At this point my only solution is to try
to buff out the light impressions, which does not really work well. It is necessary to
re-sand the surface with the 1200 grit paper to totally remove the impressions. These
impressions are light (just visible, and barely felt) but they obviously mar the finish. I
appreciate any advice you can offer. I used a furniture grade lacquer purchased at a
specialty paint store. I did not thin the product. I sprayed it on with an automotive type
You never said how long after applying the last coat did you wait before rubbing it out.
Or how long it has been since you rubbed it out. Or the brand of the finish.
I waited about 72 hours after the last coat. It is manufactured by a company here in
Fort Worth, Texas called Trinity Coatings. It is a professional lacquer. I also failed to
mention that I applied grain filler and sanding sealer before applying the finish coats.
Also, I rubbed it out by hand.
I would first wait another week or two and do the cloth test again, and if you still get
an imprint, you should call the techie at the the company and ask what you did wrong or
what the problem with the finish itself was.
My guess is (a) you didn't stir the stuff in the can sufficiently b) the batch of stuff in
the can was improperly formulated (too much plasticizer, or too much slow-drying solvent)
or c) the stuff was improperly stored in the warehouse.
My experience with this problem is that the finish eventually hardens, even though it may
take months. By the way, it is always best in every case to let the instrument sit for one
to two weeks (better still, three or four) after finishing and before polishing.
Why is my guitar
dead in places?
>I have just completed making an acoustic steel string guitar and a classical
guitar using your book GUITARMAKING, TRADITION AND TECHNOLOGY and I have a problem I need
advice on. On both guitars, on the first (E) and second (B) strings, the sustain and
overtones begin to drop off from approximately the 8-10th fret up. By the time you get to
the 14th/15th frets, these strings are very dead. Can you tell me what the problem is - -
can I correct it on these two guitars and can I do something to avoid it happening on the
Your question is pretty impossible to answer as asked: the guitar is way too complicated
for me to be able to diagnose a problem by email with the description "the overtones
drop off" or the "strings are very dead." Having said that, I will venture
that your frets or fingerboard may not be securely seated in that area.
Can this Yamaha
>I don't know how you feel about older Yamaha guitars, but my father has an FG-512
12-string, and 6years ago(the last time I played it), it sounded great and played well.
Fast forward 6 years, and it has incredibly high action, and a low bridge height. I
adjusted the truss rod as much as I dare, but it only helped slightly. I suppose the neck
angle has changed. This guitar has been sitting in a mini storage locker for about 2 years
residing in a chipboard case, and is about 20 years old. My question is this: What can I
do to try and rectify the problem on my own, do I need professional help ,and is there
hope for this guitar? It has a really nice sound and is a nice looking instrument, so I
hate to get rid of it. I think it uses a plastic glue or resin glue, so it is not easy to
do work on.
I'm an old hand with those particular guitars. It's what they all do. I'm afraid you have
to have fairly advanced technical skills to pull off a neck reset, which involves
loosening the plastic binding-- without breaking it-- from the seam near the heel, in
order to reveal the back seam around the entire front of the soundbox; then sawing through
the back seam [as well as the back/headblock seam] in that area with a razor saw. This
frees the neck, allowing you to pull it back in the direction opposite to what the string
tension pulled it to, and then glue the seam shut while the new (and appropriate) angle is
accurately held in place.
The exposed edge of the back plate will
now project about 1/16" into what was the binding slot. It then has to be trimmed
away so the binding can sit back into place. The binding is glued back and the chipped
finish touched up. The instrument emerges as good or better than new, with only slight
evidence of the surgery. The technique is called "shortening the back" because
you've now youve actually shortened the back while tucking the neck, neckblock and
sides into the soundbox.
We haven't done one of those for a dozen years, they just don't seem to show up any more.
But that's what's involved. We could offer to do it for you, but it's likely to cost about
what the guitar is actually worth or somewhat more. Even before shipping and handling
What do I do
now, Uncle Bill??
>I made a stupid mistake last night gluing up a back on a classical. I put too much
pressure with a clamp on one side- I used the clamp to augment the bands I was using-
never again. Anyway the pressure popped the center back brace loose just at the point
where I arched it. The rest of the brace is intact and it did not affect the arch.
However, the brace is slightly raised at that point near the side. It did not damage the
kerfing as the brace just touched the kerfing and was not under it. So- my question is,
should I try to reglue the brace through the soundhole by using a jig to force it down to
the back or could I just fill under the brace with a small wedge and glue to make sure I
don't end up with a rattle. Or- the least desirable option, should I take the back off,
fix the brace and reglue. This luthier art is a constant learning experience. I spent
hours getting the back
ready, re-reading the chapter in your book. And then the failed back brace.
That's a tough one. You shouldn't have to go through the hell of removing the back, not
that it wouldn't be good practice if you were ever going to become a repairman some day.
Are you? Well, with that out of the way, let's see how I can guide you, sight
unseen, by email.
The middle brace, huh? you can probably see the problem right through the soundhole.
That's why you've offered to put a wedge under the brace, because it right there in plain
No, you don't want to but a wedge between the brace and the back. You want to put a chip
at the end of the brace so that it's locked in , like the ends of the other braces. So how
1- You want to create a "jack" which is a stick that spans the space between the
top of the tip of the brace and the soundboard. Then you want to wedge it between the
brace and the soundboard so that it presses the open seam shut (when there's fresh glue in
the seam). Make the stick pretty thick, about 3/8" square (to spread the pressure)
and round the soundboard end slightly so that it lifts into place without snagging on a
sharp corner. You make a brace that is a bit too short, and then keep adding strips of
masking tape to its end until it is long enuf to press into place. It should be just long
enough to flex the popped tip down against the back.
2- Do a few practice runs until you can educate your hands to slide it in through the
sound hole and prop it in place smoothly and securely (you don't want to drop it into the
guitar and search for it while the glue is setting up).Now remove the jack.
3- There are several ways I can think of to get glue under the brace. I'm presuming you
can see it through the soundhole, and that it is actually pretty close to it. One way is
with a thin artists spatula or palette knife, the type with the offset handle, not the
straight handle. Or a bent, thin feeler guage, which is what my partner Harry uses. He
glops glue on the up-surface only and slides it in there under the brace. A couple of
applications should do it.
4- Apply the jack and let dry. You can place a slat directly over the brace, across the
top, clamping across the top and back with a padded cam clamp, snugging the back down
gently over the prop and glued brace until the glue sets.
5- Try to carve the kerfing chip above it off, and make another chip that it bigger so it
spans the distance to the brace end. Glue it in place with white glue holding it firmly
against the side and against the brace end with your fingers while counting slowly to
sixty (better ninety). That should do it.
an easier way to thin the plates?
>I'm embarking on my first classical guitar and thus far I am enjoying the
experience. I find your book to be of tremendous value to my education. Now that I've
buttered you up ,I am struggling a bit with thinning the back and sides. In your book your
mention that if you are getting chip outs and such that you should take whatever time is
required and sharpen and adjust the plane. I've made several attempts at sharpening and
even purchased a book specifically on sharpening, I believe I've made progress on
sharpening, specifically with the scraper, but I continue to get chip outs and gouges. For
the back I resorted to sanding the back with a long block sander and alternatively
scraping with a scrapper until all of the gouges have been taken away. This was a long and
labor intensive exercise. I'm just now starting the sides and have experienced the same
problem with gouges and chip outs. I'm more concern about the sides since I eventually
have to bend them. Do you have any words of wisdom that can help me? I don't want to get
Thats a fundamental guitarmaking problem that all aspiring luthiers must resolve
before going on to the next step in their evolution. Your own personal evolution from a
beginner into a fine instrument craftsman that can shave thin slats of hardwood
successfully is analogous to the larger process of how instrumentmaking evolved from a
rustic folk craft that dug out a solid block of wood to make a soundboxinto a
refined craft-guild profession that learned how to razor-sharpen hand planes to easily
shave thin slats of hard, figured wood that could then be heat-bent into elegantly curved
soundbox plates. Ontogeny recapitulates philogeny (look it up).
You didn't say how thick your blanks were to start with, but there really is no other hand
technique other than planing or scraping. Donald Brosnac actually placed a hand-held belt
sander on his plates, and had no compunction to teach others to do the samebut that
seems like a recipe for disaster. Clearly scraping is safer than planing with a poorly
sharpened and set-up hand plane. Indeed, there is a tool called a scraper plane that
allows you to hog greater amounts of material, but that also requires some set up and
The problems you are having are shared by most luthiers and is why most of them (the ones
who are too lazy or busy to develop their plane techniques) eventually obtain some sort of
abrasive planer, either home-made or store bought. The Guild of American Luthiers offers
information about shop-made devices that different luthiers have devised. These devices
are generically called "filletiers", from the French. The other alternative is
to check around in cabinet shops in your area and ask whether any one has an abrasive
planer (or a wide-belt sander) can reduce your plates accurately for a fee.
surface geometry: ruminations
>I have a question for you concerning the fretboard surface geometry. In my day job
I program and run CNC milling machines. It is relatively easy for me to develop surface
geometry with compound curvature on computer, and to generate toolpath to cut the material
on the CNC.
I have read somewhere about curving the fretboard from end to end to account for the
waveform of the vibrating strings, and to vary the cross-sectional curvature for a more
comfortable feel when fretting the string.
I am generally assuming the curvature could be derived from understanding the waveforms of
strings 6 and 1, then allowing the software to interpolate the transitions thru the other
strings. I don't know, however, about factors like neck deflection due to string tension,
how to measure the string waveform, how much to curve the cross-section if at all, etc.
I am contemplating generating toolpath to apply this curvature to the fretboard and to cut
each fret slot. The slots would also conform to the curvature accurately. The mill has
very good precision (x.xxxx").To this end, can you recommend any good method of
determining the correct curvatures?
Luthiers, at least myself and all the ones I know, approach fretboard geometry from a far
simpler vantage point. We let string tension curve the fingerboard to create
"relief" (clearance, which will occur naturally as a result of six strings
pulling up and slightly curving a slender neck). The curvature is then controlled back
with an adjustable truss rod towards a contour that is more appropriate to the player's
attack. Heavier attack, more curvature; lighter attack, less curvature. The adjustable rod
is necessary because the precise response of a neck, of precise stiffness, to the precise
tension, of the precise set of strings, of a precise string length--is pretty inscrutable
to old-world woodworkers like us. Thus the great utility of an adjustable truss rod.
For almost a century, The Martin Company postured that their necks responded so
consistently and predictably that an adjustable rod was unnecessary. During the nineties
they finally gave up that fiction, after for decades dealing with expensive neck warranty
repairs that could have otherwise been simple adjustments if they had deigned to use
adjustable truss rods (they instructed their warranty repair shops to adjust the neck
curvature by refretting part of the neck with frets with larger tangs!!!) Well the new
generation has gotten rid of all the old problem stuff that the old would never change
because the older was so hidebound. But I digress
The common visualization of the longitudinal curvature of the fingerboard is that the
string generates an "envelope" when it's plucked which looks something like an
elongated leaf shape, and the neck's curvature should "mimic" the strings
curvature. This allaws the string array to be adjusted closer to the fingerboard without
buzzing. If the neck remains perfectly straight after the guitar is tuned up to tension,
the action will have to be set very high to avoid buzzing on the lower-pitched notes when
plucked energetically. The harder the string is plucked, the wider the leaf shape. As I
understand it, the lower the pitch of the string, also, the wider the swing of the string.
So the rod is adjusted to accommodate the worse possible scenario: it must give the low e
sufficient "room" to vibrate when its plucked unfretted. As you fret it closer
to the body, the fingerboard surface will tend to go toward straight, which is all right
because at a higher pitch, the vibrating string doesn't require as much relief. So the
idea is to tighten the rod (straighten the neck) until the player, playing energetically
(each player has a different idea of what "energetic" is) starts to hear a
rattle, then backing off a bit. That is what is meant by 'the fretboard should follow the
shape of the vibrating string'. But the shape is not cut into the wood. It's generated by
the string tension and then controlled by the adjustable rod.
By the way, there is another intractable variable that many builders account for: the neck
and fingerboard more or less consistently being bent BACK by the wedging action of the
frets. Some luthiers account for this by gluing a longitudinally straight and already
transversally arched (and slotted) fingerboard to the neck; then tightening the rod to
induce a BACK bend into the neck; then hand planing the hump off along the run of the
strings until the fingerboard is straight (but still arched) again. This "loads"
the neck and gives the adjustable rod action in both directions. Unfortunately, this is
not something that can be CNC'd very easily.
So in the end, I shape the fingerboard straight along it's full length, along the run of
the strings. String tension and the truss rod will take care of each other.
But thats easier said than done, no? Along the run of the strings means
you have to consider the rate of convergence of the string array towards nut in order to
accurately shape the fingerboards so that it will be straight along the run of the
strings. But most factories and luthiers dont do that. They operate on the
assumption, the fretboard is a tapered surface section of a cylinder rather than a tapered
surface section of a cone. The latter though is the true case, not the former.
Factories subscribing to the former, arch their fingerboards blanks on a shaper using a
cutter with a semi-circular cutting edge. This imparts a uniform cross-sectional curve
along the entire length of the blank (making the fretboard surface a section of a
cylinder). However, after the fingerboard is tapered and the strings are placed so that
they converge towards the nut, the result is that these same strings will see a slight
hump in the board. This effect becomes also apparent after luthiers sand
the arch into the fingerboard using a curved sanding block stroked longitudinally up and
down the length of the fingerboard blank. The result is a puzzling hump, or
backbend in the fingerboard which inevitably appears after the fingerboard is
glued to the flat neck-shaft. In many cases the string tension will iron out the problem,
but if the neck is too stiff, the hump will persist and dog the luthierand the
eventual owner of the guitar.
Those who ascribe to the latter visualization (a surface section of a cone)--which to my
mind IS the proper configuration--cannot simply rely on shaping or sanding the board along
its length, since the transversal radius should be constantly changing by a minute
amount as the fingerboard widens. For us, the only recourse is to follow the preliminary
machine shaping or block-sanding techniques above, then recontouring it by hand: hand
planing it using a straightedge as a guide along the run of the strings. The
beginner will realize that this requires some advanced hand-tool skills. The recommended
fingerboard hand-planing sequence is detailed in my book.
Shaping the blanks on a CNC machine should, indeed be able to create a complex curved
surface with a constantly- growing transversal radius. As for me, sadly, I have no CNC
machine, so Im doomed to rely on my hand planing skills. So if you want to CNC your
fingerboard, determine the splay of your string array (the spread at the nut vs. the
spread at the saddle). This determines the inboard limits of the fingerboard width and
taper (i.e., its outline). Then determine the minimum arch. This can vary. It usually
matches the natural curve your barring finger traces when its extended. Interestingly,
strong players prefer it to be slight, weaker players like it more prominent.
The bridge pins
contribution to acoustic coupling (cont. endlessly)
>I built my first guitar this past summer and am interested in some of the articles
on your website because I want to improve the quality of the next one. One question has to
do with the pegholes in the bridge for attaching the strings. I have your book and have
read everything I can but have never seen this addressed. The ball ends fit thru the holes
to under the soundboard. Some authorities suggest slotting the holes on the soundhole side
of the pegholes for string clearance. I built a little saw from a narrow jigsaw blade with
no set to do this. After doing it, it became apparent that I could saw all the way so that
the string lays in the sawcut instead of the peghole, thus causing the ball ends to pull
up on the soundboard. I am confused, though, because all available pegs are grooved for
the string. It seems to me that pulling the strings into the sawcut so that the ball is
tight against the inside of the soundboard would most efficiently transfer string
vibrations. Am I missing anything?
You can purchase bridge pins with or without grooves. This is for folks with different
perceptions of what's going on there. My favorite bridge pin source is www.fossilivory.com where a lot of bridge pin
questions are answered.
My view is that the string's vibrations
are directly and adequately transferred to the soundboard regardless of how, precisely,
the strings are attached to the bridge. Where else could the vibrations go? My perception
is that the acoustical signal is coupled regardless of how much of the string is in actual
contact with the bridge. I view it something like soldering a braided pickup wire. The
signal gets through whether there is one, two or three strands touching the lead. So, from
my vantage point, the only conceivable way you could have some "loss" of
vibration (i.e. damping) is to encase the end of the string in a rubber plug and insert
the rubber plug in the bridge. Even doing that, the effect on the tone would be slight:
remember that the strings tension, and the portion of it that makes up the signal,
is mainly coupled to the soundboard through it's pressure the saddle. Now if the saddle
fits poorly, that's another issue we can argue.
My perception is that concern about the shaping of the bridge pin hole and the clearance
notch amounts to purely a usage issue: If carelessly done, the pins jam so you have to
forcefully pry them out to remove them, or they fall out on their own, or they are ejected
across the room when you tighten the strings. To avoid this problem, the string and pin
can't compete for space in the hole. But the pin has to tighten into the hole.
Oh, and the ball end doesn't come to rest on the sound- board. It comes to rest on the
Oak for guitars?
>In the section on side bending, you suggest that Oak is a Really good material for
side bending & with this in mind I have found a beautiful piece of Quartersawn Clean
English Oak, with no grain run out. This is what I intend to use for the back and the
sides of the guitar. There is also enough oak left for the guitar neck and headstock, but
I am not sure if Oak is a suitable material for the neck and cannot find any mention of it
in your book? My main concern is that although the piece left is perfectly quartersawn, I
worry that steel strings will put too muck stress on the neck. Is it a hard enough timber?
Can you please advise? A friend of mine has a really nice, All Oak, hand built classical
guitar that is quite old and has always played well, but obviously there is less stress on
the neck, as the strings are Nylon. If you consider Oak not to be suitable for a steel
strung neck, can please advise of a suitable material that would complement the oak body?
Oak, as long as it is unquestionably well-seasoned, straight grained and quarter sawn is a
suitable "hardwood of opportunity" for guitarmaking. It is sufficiently strong
by far for steel-string guitars. Its drawbacks? Huge pores which present finishing
challenges. Glass-hard end-grain and a tendency to splinter which presents carving
challenges. If your tools are razor sharp and you have the proper finishing resources,
these challenges can certainly be overcome. Finally oak is reactive to humidity changes,
so unlike Honduras mahogany, it is chancy to use, particularly for necks. If you must,
choose the straightest, most uniform-texture, most vertical-grain sample you can. Good
Leave no vapor
barriers under the bridge!!
>William, I'm building my first classical guitar and am ready to glue the bridge to
the soundboard. You indicate that I should seal and fill the bridge prior to gluing as I
will finish the guitar after the bridge is glued. Is there a problem with the gluing
surface of the bridge if I have sealed and filled with shellac/pumice/oil? I plan to
French polish the guitar. I will use Titebond as the adhesive. By the way, great book! I'm
having a lot of fun building the guitar.
Yes, there certainly will be. The glue won't wet the sealed wood, and the glue will
certainly fail. I 'm sorry if the book was unclear on this point: you're supposed to fill
and seal only the surfaces of the bridge that will get finished, and leave bare the
surface that will be glued. I thought it would be self-evident. I would think that
thorough sanding of the bottom of the bridge, and perhaps some wiping down with the
solvent you used for the filler--and then re-sanding when dry would suffice to allow the
moisture in the glue to penetrate it.
How would it
sound if I...
One of my tutorial students writes: >I am building two Gibson jumbo guitars, with
plans supposedly "smuggled" out of the Gibson factory (the X-bracing is very
similar to a Martin). One with Wenge back and sides and the other Indian RW. Both will
have Red Spruce tops and bracing (a former Gibson employee told me to go thick on the
tops: between 0.130" - 0.140") . I am somewhat unfamiliar with the bracing, and
I was thinking about experimenting a bit with one of the guitars bracing a bit, to wit: I
am curious if you have ever butt-joined any of the finger or lower tone braces against the
X-braces (similarly the soundhole braces against the Upper Face Brace and X-bracing)
rather than than taper them ? How did/would this affect the sound - in your opinion ?
Would this prevent the top from vibrating in its mutlitude of directions ? How would I
need to adjust the cross-section of the bracing to accomodate this "tightening"
of the bracing?
[More novel bracing proposals follow in the query]
Let me know if any of this makes sense. I know that a lot of the tinkering with
bracing that people do (e.g., scalloping) does some, but relatively little to alter the
sound. I am curious if, for example, combining tightening up the bracing while reducing
the mass of the bracing wood might change the sound (hopefully in a good way). I would
likely just run the experiment and find out for myself, but I thought that I would ask you
first, if there is a liklihood that my ideas are really counter-productive; why waste
quality wood, eh ?
Your email asks questions that simply, I can't answer. It is difficult to gauge the effect
of one change on a guitar, let alone multiple changes. You can't expect to dream up a
bracing scheme and then ask someone how it's going to "sound." I wish I could do
that! I'd be writing you now from the French Riviera. Or, I could come back with some
expert-sounding gobbledygook about "loosening up the vibrations" but I don't
want to waste your time or mine.
Regarding soundboard design, all I can give you is what I've already given you: the
outcome of my personal process of soundboard design refinement--The details of which are
in my book, and in the soundboard instructions that you followed while taking my tutorial.
If you have the desire to do something different, you've undertaken your own journey. I
can't tell you where it will lead you. What would happen if you tied the minor face braces
into the kerfing? Damned if I know. I don't do it. Do it and find out what the effect is.
The only thing I can respond to the plethora of questions you have, is that they all seem
to add up to stiffening up the top, and limiting it's range of response. I don't know what
you or your Gibson advisor expect to gain by adding more mass or buttressing the top even
more massively than the "norm". I'd advise against everything you've proposed,
but would be unable to explain why in specific terms, except that it is pretty much
diametrically opposed to my entire approach: which is to create an optimally minimum
[i.e., optimally efficient] structure in the soundboard. I'm always asking, how can I
brace this more efficiently? Not, what would happen if I beefed this up? Or increased the
top thickness by 30%?
I'd also be extremely skeptical of any Gibson insider counseling massively thick
soundboards. These may be the same voices that nearly drove Gibson to ruin after they
choked the market (mainly by selling them on Gibson's past laurels) during the seventies
with hundreds of thousands of awful, terrible acoustic guitars that, while massive and
crude in construction, nonetheless collapsed in all kinds of unrepairable ways.