William Cumpiano's 
String Instrument
Newsletter #20
















Cracks, mistakes and swivel vises...
© William R. Cumpiano 2001, All Rights Reserved

My just-finished guitar just…cracked!

 > I just finished my first guitar based on your book. I went to buff the finish and noticed a crack in the sound board. It runs from the bridge to the purfling at the bottom of the sound board. It's not a surface crack as it goes through the sound board and is about 1/32" wide. This just about broke my heart. The guitar is beautiful with a nice rich full tone. Anyway, can you recommend the best way to fix the crack short of replacing the soundboard? I'd appreciate any advice.

What part of the country are you in? Has the heat gone on in your workspace and you kept the guitar too close to it? What is the humidity in your workspace? Under 40%? Did you close the soundbox in a high humidity environment, and now are buffing the guitar out in a low humidity environment? That's how cracks occur--if not from hidden flaws in the wood

1/32" wide is a BIG crack. Is it really 1/32", or is it just a hairline that looks real big because its so worrisome? Can you see light from a small lightbulb placed inside the guitar, through the crack? When you press on the wood on the right of the crack, does the wood on the left side move too (i.e. is it indeed cracked through and through?)

Closed hairline: vigorously rub white glue (i.e., Elmer's) into the crack with a clean finger in small circular movements on the outside for a full two minutes, replenishing it from the bottle often, and wiping the excess off periodically with a damp paper towel-- and, if you can get your arm into the guitar and reach the crack with your finger, put some glue on your finger and feed glue into the crack from the inside also. Let dry overnight and then carefully wash the excess glue off the outside with a damp, not wet, paper towel.

Open crack (if indeed it is 1/32"): Get a large plastic bag that the guitar can fit in. Put the guitar in it, but before tying the opening up, take a water-filled pump bottle that delivers a mist spray, and thoroughly mist the inside of the guitar through the soundhole and mist the surface of the guitar on the outside. Now seal up the bag tightly and put it aside. Next day, open the bag and take the guitar out and examine the crack. It should have closed some or closed completely. If it isn't fully closed (a tight hairline, instead of an open crack), then repeat for one more day. Then remove the guitar and follow the instructions above for gluing a closed hairline crack. You can then scuff up the finish in the crack region and either respray the area, or neatly brush a line of fresh lacquer over the crack. You may have to repeat this a couple of times. Let the lacquer dry and shrink for several days before buffing out. If you brush it on and then buff it out soon after applying, it will shrink and leave a finished groove in the lacquered surface.

This is one reason why you should build the guitar within the shortest possible time frame. If you build over several seasons, all kinds of mayhem can occur. Live and learn.

Thanks for the advice. I started the guitar at the end of July in Rhode Island. I had to put it aside after I applied lacquer to the box when I had some problems with the neck. The heat did come on and the humidity dropped  from about 45% to 25-30%. That's probably what caused the crack.

The crack is 1/32 wide! I tried applying downward pressure on the soundboard and the crack closed some but not completely. When I first noticed it, I put a light in the soundbox under the crack. I could see the bulb.

I will try your suggestions. Although it's disappointing to have this happen to your first guitar, I look at it as a learning experience. If you’re going to make guitars, you probably should know how to repair them as well.

Chalk it up to the cost of an education!

Hello Bill. How's things? I have a query regarding the repair to the top of my second guitar made of cedar and mahogony. The friend I sold it to wanted a gloss finish after the fact. I said ok but I'd have to remove the bridge. I've only removed one bridge before on my first guitar and it came off quite easily. This guitar's bridge was glued on with titebond. I am aware of the higher heat needed to loosen the bridge and thought I had achieved this, however, the bridge came off but so did sizeable chunks of cedar including two centimeter square pieces infront of the bridge. I thought I had scribed sufficiently around the bridge. Be that as it may, chalk it up to experience. What I am curious about is whether, having glued cedar inserts under the bridge area and sanding down to below the outside chips, I should glue a bridge patch overlay to strengthen this area. The top is quite thin now, as you can imagine, in the bass area. Top and bridge plate combined equals approx. .200". Because it is cedar I made the braces slightly oversized and the top was over built to begin with. I'm not all that confident that the bridge area can take the stress because when I push down behind the bridge area I can see the top give a little. Anywho, I realize this is a long distance affair here but, given the materials, the thickness at the bridge, and of course my anxiety do you have any suggestions

Alas, Having access to a professional luthier for unlimited Q&As has driven more than a few beginning luthiers to a state of innocent hubris where they feel that they can try anything and then sell it to somebody, because they can always call the Cumpiano emergency squad when things go badly. I've had more than my share of "look what happened, uncle Bill -- NOW what do I do?" and sometimes I simply don't have the magic answer to all the possible ways that beginners can get themselves into trouble--sometimes big--trouble. This is one such case.

 1- you don't sell your first, or your second, or your tenth guitar to anybody. That's because you still don't know how to fix them. You haven't mastered finishing and you're confident enough to do REfinishing on someone's property? That is another skill--let alone bridge removal--that you have to learn before you can even contemplate selling your work, because your customers will track you down, find you and nail you to the wall.

 2- you don't try to remove a glued bridge on a guitar if you don't KNOW how to remove a glued bridge on a guitar. Disaster is inevitable. ESPECIALLY on a butter-soft cedar top. You practice first on glued-up scrap, and NOT on a customer's guitar--yours or anybody else's!!

 Yes, sure go ahead, patch it up the best you can. Maybe the customer won't mind the scars. What else can you do other than replace the top?

 Oh. You don't know how to replace the top.

 I don't know what your career plans are regarding guitarmaking. I don't know if the guitar's owner is a forgiving friend or an angry stranger. My best advice is give the guy his money back and take the guitar back. And chalk it up to the cost of an education.


What about those wooden dishes for making tops and backs? …and swivel jaw vices?

 > my congratulations for being in the new book "Custom Guitars". I ordered it from StewMac and are looking forward to see it.  I would like to ask you two questions and hope that you can answer as soon as your time permits.

> 1) I always loved "your" guitar makers vise. The only source I know of is   Stewart Macdonald in the U.S. High Dollar, postage and customs fees make   ordering a luxus for us Europeans. Do you know the manufacturer? Is it   perhaps made in Germany?

The guitar making vise sold by Stewart Macdonald is an Asian copy of an identical vise of far greater quality that sold for less (fifteen or so years ago), made in Germany by Ulmia. The Ulmia Universal vice now costs about $600. So be glad Stew Mac is selling a copy for only a couple of hundred dollars. So it isn’t as nicely finished, and wobbles when you turn the screw. So what? It tightens and doesn’t mar the lacquer if you line the jaws with thick sole leather. Lately the jaws have been coming through (inexplicably) oval shaped. Useless. I replace them with square hardwood jaws with rounded corners.

> 2) What do you think about those concave wooden dishes used by so many for making tops and backs? In my humble opinion I don't think that a guitar made with geometrically exact semi-spherical top or back will be better. At least I hope so, because you don't care about that in your book. "Your" back is cylindrically shaped and the top curvature is "just domed" (fitting for instance the X-braces to a concave form requires to plane or sand the underside of the braces in two axes).

>Using and making huge dishes is an effort I want to avoid if possible though
I also like the idea of having everything well defined. Or do you use dishes for building your guitars now?

> Thank you for your time
> Best regards
> Martin Koch
> www.BuildYourGuitar.com
Those concave dishes can be easily (and expensively) purchased from supply houses, but if you think that simply pressing a rosewood plate into a dish will somehow cause it to retain a hemispherical shape, you will surely be disappointed. The moment you release it from the dish it will only retain the shape given it by the braces. So glue the braces using the back slats I recommend and save yourself the trouble and $$. Besides, your braces’ gluing surfaces would have to be shaped to match the hemispherical surface to make accurate contact, would they not? So something is going to get distorted somewhere, it would seem.

The back is curved slightly to stiffen it, and tipped forward to de-symmetricalize the soundbox to avoid standing waves. A measure of longitudinal arch is applied to its edges by shaping the rim of the sides. That's all I need to know. The stuff about it being a curved reflector of sound is also a lot of hooey (American slang for bull @#$&). Acoustic waves spread in all directions from the source, and penetrate the back. You can hear the guitar's sound by listening from the back, can't you? Would you be able to if the back reflected the sound forward?

Headstock angle query…

> I am building my first classical guitar and am using your text as a  reference. I am also using plans that I purchased from the Guild of American Luthiers. The guitar I am building is based on Julian Bream's '73 Romanillos design as drawn and measured by Kevin Aram. I believe this guitar was originally based on a Hauser design.

>Your text refers to a headstock angle of 15 degrees. The Romanillos has an angle of 7 degrees. If I choose to make the headstock at an angle of 7 degrees what are the repercussions? The instructor that I'm working with says the shallow angle will impact the action by making the strings more susceptible to buzzing. Do you think it will do anything else.

Since it is my first guitar I am planning to use the numbers as mentioned in your text with the exception of the soundboard (I actually haven't read that far ahead yet). But your input is much appreciated.

I don't know which is angle is "better." But here are my thoughts:

I'm aware that Hauser used a 7 degree headstock tilt. I would agree with your instructor that it would make the strings more susceptible to buzzing (a very perceptive observation, I might add) since the "back angle" of the string is reputed to affect the snap back of the string when its plucked. The steepness of the back angle, or the angle that leads up to the nut or saddle, affects the downward vector of the tension forces (the string pushes harder, as it were, on the nut or saddle, as the back angle is steepened). It also affects the amount of torque dumped onto the headstock itself. That describes the effect on the static forces acting on the neck, but it's anybody's guess as to what the precise acoustic effects are. One can surmise, based on the noticeable loss in power and punch of a string as the saddle is cut down, an action which flattens the back angle.

I'm sure Hauser also used a 15 degree tilt on other guitars he made, because he was a renown adherent of Torres' design philosophy, and that's the angle on many Torreses. My feeling on the matter is that the headstock tilt affects the "feel" of the strings more dramatically than it does the sound, but that it certainly must affect the sound "envelope," in some way--that is the length of the ASDR (attack, sustain, delay and release) of the note, since this is affected by the tautness of the strings. . I would personally shy away from flattening the headstock angle because I would be concerned about the attendant losses, but who is to argue against what the great Master did

Another effect of a flatter headstock angle is an attendant increase in the gluing area of the headstock scarf joint--which is good. That perhaps may have been the priority for Hauser during the period he was doing this. More gluing area means more strength. May Hauser was having problems keeping his headstock joints together.

Change in truss rod cap recommendation

> Help,
> Please confirm the measurements of the bearing cap shown as an update. Your more massive cap seems to have shrunk some in height and width and  gotten thicker only. The old way you drilled through the 1/2" side with 3/16 & 13/64 and now its through the 1/4 " side leaving very thin sides is this correct or am I missing something? the old cap was 1/2 x 3/4 x 3/16 and the new is 1/4 x 1/2 x 5/8 (.625)
Yes this is a better design, although it requires a bit more precise drilling. However the earlier (vertical) cap tended to rotate under tension and sometimes jam. The longer, lower (horizontal) model holds on to more of the rod's length and stands up to more tension with less distortion of the rod.
Cutaway tips and plans

> First let me say that your book has been a valuable resource in my shop. I
couldn't have made my first guitar without it. I am planning to build a cutaway steel string for my next guitar and was wondering if you had a set of plans you would be willing to sell me. I have a set for a dreadnaught but I'm not sure how to adapt it to compensate for the cutaway (especially when it comes to bracing and increased depth). If you don't have a set of plans, do you know where I can get one or, can you help me with the compensation problem? Any advise or direction would be greatly appreciated.

Thanks for your message. I'm afraid I don't know of anything published on the matter, but I hope to publish a series of plans in the future. The only thing I can note about cutaway design is that:
· The upper transversal should remain full length, and not be interrupted by
the cutaway.

· The cutaway steals soundbox volume from the guitar, so a jumbo with a cutaway is a not so jumbo guitar anymore, and a small guitar with a cutaway is a large ukulele. You can account for the loss of volume and attendant bass response by lightening up on the braces, widening the lower bout, and/or deepening the body.

· Don't use the pinning system described in the book, but instead use the barrel bolt system described on my webpage. You'll love it

Japanese chisels?

 I'm building my first guitar, but have experience working with wood. I'm now considering buying some new quality tools for this endeavor, but would value your opinion first. Simple question. Are Japanese (hollowed back) paring chisels and bench chisels appropriate or does their hollow back pose a problem as opposed to Western style( Marples,Sorby ) chisels? By the way, your book has been a huge inspiration, thank you.
Japanese chisels are fine, but you may not like how they handle carving the concave curves at the heel. The extra long blades of the paring chisels make brace carving go somewhat easier. I would suggest the longest-bladed chisels you can get for that purpose. But I wouldn't mind owning a set of japanese chisels myself, actually.

Truss rod adjustment during construction

> In your book, you mention that after gluing the dimentioned Steel-String
finger board to the neck, and checking for flatness, that the tension rod neck needed to be tightened until a deflection of 1/32 to 1/64 was obtained.
Is much force required here?
> Couldn't find any prior mentioning of further reducing the width of the neck. Wouldn't this help in achieving the initial deflection?
No, the truss rod is strong enough to deflect the uncarved neck shaft and fingerboard by the amount required, without forcing it. Once the fingerboard i planed flat again, the truss rod will be pre-loaded, which will allow it t flex the neck in either direction after the neck is carved and the fngerboard is fretted. (Indeed, the neck is often deflected back by a tiny amount as a result of the wedging action of the frets. If the rod has been preloaded, it can be released and the neck brought back up to true this way.) 

Bending herringbone purfling

> I've purchased a few strips of herringbone purfling and am concerned on the best method of bending around the waist area of the guitar. Then bending will be against the longer width of the cross section. Hot-bending perhaps? thanks.

Did you think it would be easy to bend a rectangular strip made up of a million tiny pieces...the wrong way?

Clearly, you have the wrong cross section for an easy job. The thin flat herringbone is best for straight line inlay work (like decorating the back seam), not for curving along the perimeter. The stuff indicated for what you want to do has more of a square cross section. Those you can tape together and bend along with the binding strips quite easily.

But that's not your problem. You want to do it the hard way. So expect a high possibility of failure. Maybe the following tips will help.

Place the strip in scalding water for a minute just before gluing it in, towel the excess water off and apply the strip with white glue along with the binding strip while its still wet and warm. It will either conform with no problems (assuming you don't have some crazy bend) or it will delaminate. Sorry--but I told you may have problems. It depends on whether they used hide glue to make the herringbone or some random heat/moisture resistant glue. You'll just have to keep your wits and keep applying the delaminating pieces until you gone past the danger zone. It usually works out all right.

If you brook no failure and are absolutely terrified of it, you'll have to go to the trouble of routing a slot into a scrap piece cut to the same outline of the guitar, similar to the slot on the actual guitar, soak the piece like above, and tape it gingerly into the curved test slot. When it cools and dries it will retain the curved shape ready for applying to the actual guitar. If it breaks, you can save the curved fragments and inlay them in sections on the guitar.


Neck bolt fastening method inquiry

> Hello William, I believe that I'd written you before. The purpose of my correspondence today is about a article of yours that I'd read at the MIMF. You say that you're now attaching the neck to body joint with these KD fasteners. If I use that method, would anything have to be done differently up to that point than what's written in your book? I'm in the process right now of building my first guitar & last night I'd taken all of the clamps off
of the laminated heel that I'd created, cleaned the area up & then marked my centerline down the shaft of the neck. So you can see that it's soon going to be time for me to start thinking hard about how to go about the joining method. I hope that everything is to be done exactly as in the book up until one comes to the pins in the neck/body joint. I'm hoping that the KD
fasteners will be the only difference. Please respond!

The pinning method in the book can be easily upgraded to a barrel bolt method. First, read the corresponding page in my website.

Its the same headblock and neck tenon design as in the book, except that you have to forget about the pins but drill the headblock for the barrel bolts. The page shows how to drill the neckblank from scratch (far easier BEFORE
the tenon has been cut and the heel shaped) but you can still drill the tenon nice and square for the barrels AFTER the tenon has been sawn and the heel shaped by fashioning a small homemade drilling jig that fits over the tenon which guides the drill perpendicular to the tenon. The bolt holes in the headblock and the tenon are drilled oversize to accomodate the tiny neck
angles and misalignments, but the transversal hole for the barrel has to be very snug. Most barrel bolts are made in Europe so they are millimeter sizes. You must obtain the precise mm drill so the barrel press-fits into its hole in the tenon.


Sanding boards…
> Can you please tell me the how thick of a board you use for your sanding boards (large & small)?

The last sanding board I obtained from a kitchen counter place that had stacked away several sink hole cutouts which were perfect. They were flat, about 3/4" high-grade plywood, lined with laminate on both faces. I use used wide-sander belts, 80-grit, placed side by side and adhered, not with contact cement, but with high-tack spray adhesive, so they can be removed and replaced. You can just as easily use regular sandpaper sheets side by side, except that you will need more of them.

As far as small sanding boards, they span the gamut from postage-stamp size to headstock size to fingerboard size, on literally anything that will keep them flat and fits in the hand. 


Try this!

> I am building a classical guitar using your book. I misinterpreted your statement about reducing the headblock height for the soundboard. I reduced the height, but not by enough. The soundboard is about 1/32" too high. I was planning to scrape the soundboard flush as you stated, but I am afraid this might be too high for this procedure. Unfortunately, I didn't think this was too high until I began to fit the fingerboard. Since I am following your book, this is after the binding has been glued in and scraped flush. Inexperience and not thinking all the way through the construction of my guitar strikes.

> The only options I can come up with are reducing the thickness of the soundboard until the fingerboard fits, or routing the bottom of the fingerboard to allow it to fit over the soundboard. The soundboard is cedar with a thickness of ~.115".

How about laying a 1/32" mahogany veneer on top of the neck shaft?

A questioner from Italy asks about the high action on his classical
> I own a 20 years old classic guitar. It is a good guitar finely builded with > selected spruce top and rosewood sides.  It is in good condition but have high action. I have lowered the saddle about 3/64" (now the exposed saddle is 4/32" at the treble and 5/32" at the bass), but the action is still high; 5/32" at the treble and 6/32" at the bass (12th fret). My prefered action is 4/32" at the treble and 5/32" at the bass. How can I lower the action?

> Do you think that these high action is caused from my strings? (I have always used "Daddario pro artè j46 hard tension" or "Savarez yellow label" for 20 years). Can using lower string tension prevent this problem? ("Daddario pro artè j43 light tension" have a tension of 78,2 lbs and "j46 high tension" 86,9 lbs. Not too much difference...)

This unfortunately occurs with classicals, even good ones. The cause for your high action may be none, or one or more of the following:

· The original selection of one or more pieces of wood on the instrument which may not have been seasoned adequately. They may have shrunk over the years and distorted the instrument.

· Not keeping the guitar in a case, and leaving it out in strong sunlight.

· The swelling or shrinking of woods in an environment which swings from wet to dry extremes. (Are the ends of the frets sticking out from the edge of the fingerboard? That is a sign of a harsh environment)

· Excessive string tension possibly but not very likely, unless you can see a distortion of the surface of the soundboard also. The strings on a classic exert less than a hundred pounds (45 kilograms) which is not very much when you consider that steel strings exert 90 kilograms.
You can reduce your saddle height removing material until what remains is 2/32 treble and 3/32 bass and achieve your desired action, but unfortunately the lowering of the saddle to an extreme may reduce the sound volume of your instrument. I would try to do so, and see if it really does reduce it to a undesired degree, if so, you'll have to repair the instrument to lower the action without lowering the saddle.

The work required to do so may be expensive and will require a skilled luthier to perform. Depending on the circumstances the indicated repair may be to remove the frets and plane the fingerboard to a different slope and then refret, or replace the fingerboard if that is not sufficient (i.e. if the fingerboard is too thin to start with). There is no easy way that I know
to move the neck back on a classic guitar (which is what your guitar needs), although what works sometimes is to remove the fingerboard and heat the neck and press it back while it cools, and then reattach the fingerboard (if it is not damaged beyond repair when it is removed) after it cools, if the neck has taken the desired set back.

But that is complicated and may conceivably scar the instrument. It depends on the care and skill of the repairman and more than a bit of good luck.

arrivederci e buona fortuna

Cocobolo: any good?
I want to use Cocobolo for the backs and sides of the next classical that I build and I am being warned that it is a terrible wood to use. However I also read how many call it the next Brazilian.

Cocobolo is a magnificent guitar tonewood, as beautiful as any--extinct or plentiful--available today, and as technically sound and acoustically lively. It glues well (Titebond) and finishes well (use a shellac or vinyl sealer undercoat under the lacquer).
Over the years I've purchased several large planks of it and have sawn it up and used it with terrific results. I personally have never experienced any of the handling effects that have been attached to it: rashes, asthmatic attacks, hyper sensitivity--and I have been literally covered in the dust. But that is not to say that someone else may not react allergically to it. Some people react violently to ANY wood dust, some to certain specific varieties. I've been blessed with no reactivity to wood or finishes or glue, save for the usual minor physical side affects of getting congested if I don't use a dust mask, or occasional and transitory itching in some rare cases. Oh, and I've lost my sense of smell, which returns periodically. But that's because I've been working around wood dust for thirty years, and my doctor says that some resins imperceptibly irritate the olfactory receptors in my nose and they shut off. I’ve been using a nasal steroid spray for that.
If you have it and don't react to it, use it and enjoy it!