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William Cumpiano's 
String Instrument
Newsletter #17

CLASSIC BRACING 2000

BOOK AND WEBSITE INFO MISMATCH

CLASSICAL NECK ANGLE CONFUSION

HOW ABOUT FOUR PIECE BACKS?

IS THE NEW NECK BOLT SYSTEM PUT TOGETHER DRY?

DO YOU RECOMMEND USING THE NEW SYSTEM ON CLASSICAL GUITARS AS WELL?

12-STRING STRUCTURE DESIGN UPGRADE

TIE BLOCK BRIDGES ON STEEL STRING GUITARS

PROS AND CONS: HEADBLOCK VEE JOINT

CORAL NUTS AND SADDLES?

AVAILABILITY OF CARBON FIBER TOPS

SETTING THE NECK ANGLE ON THE WORKBOARD

"...THEN I HEARD A CRACKING SOUND!"

GUITAR KIT BOO BOO

WHY TAPE UP THE DOUBLE ROD?

NECK SCULPTING

COPYING A GUITAR

No time to write new stuff...too many letters to answer!
William R. Cumpiano 2000, All Rights Reserved


CLASSIC BRACING 2000
About a year ago I had brief correspondence with you concerning lattice bracing for classical guitars. At that time you said you were checking into it with a luthier friend of yours. I have since seen mention of it on your web site. Do you have any diagrams/details/dimensions available, or know of any web sites with info as I have never really seen what it looks like, I have just read that it is a viable option to traditional fan bracing. I also noticed that Martin uses it on some their classicals. Thanks for any insights you may offer.

No, I'm afraid I don't have what you ask. But I'm even more convinced than ever that this scheme amounts to Classic Bracing 2000. There are dozens of approaches: Alan Chapman uses an exceedingly fine soundboard with a very fine grid of criss-crossing braces (with thin strips of graphite glued to their tops) that travel all the way to the sides and up to the upper transversal (he dispenses with the soundhole in the usual location, and places two smaller "ports" above the upper transversal. Tom Bazzolo places a three-finger tic-tac-toe just under the bridge. Both get truly outstanding results. All thin the lattice array as they approach the sides. You'll have to go it on your own!

BOOK AND WEBSITE INFO MISMATCH
Bill, Correct me if I am wrong, but if I use your hardware neck joint as described on your web page, the rod notch in the headblock should not be 7/8" deep as it is in your book. If it is, there is not enough room to drill the upper bolt hole in the mortise. At least the way I did it there isn't. (Of course I am pretty good at goofs). I am going to have to glue a small block of wood to take up the slack in my rod notch and hope it will be strong enough to hold. P.S. Even with the problems I've had building this thing, I still love doing it and think your book is great.

You're so right. The book was written in 1985, before the hardware joint was even a gleam in my eye. Some extrapolation is necesary. I'm working on a new set of headblock and joint three-view diagrams which I will upload to my webpage soon. But your solution should hold. The top bolt is just for alignment, since the neck is actually pushing INTO the headblock up there. The top bolt just has to be a little snug. The bottom bolt is carrying the load because the tip of the heel is pulling AWAY from the body. You shouldn't have a problem.



CLASSICAL NECK ANGLE CONFUSION
I'm just about to glue the back on the classical guitar I'm building and I'm a little confused about what the neck angle should be and how it's determined. I've looked in your book and instructions are given regarding a steel string, but it appears that a classical angle just is whatever it is. There is still room for adjustment depending on how thick a shim I put under the neck when it's on the workboard, but I can see that even this would change once the back is wrapped and the shim supporting the sound board is compressed. Once the back is glued, there doesn't seem to be anyway to adjust this, except maybe by tapering the fingerboard, which I've already done. Am I missing something in your book, or is this something I don't need to be concerned with?

The precise slope of the top of the fingerboard, relative to the bridge, is one of the most crucial factors in the quality of the guitar.

You're all right if the neck shaft and the rim of the soundboard exist on the same level plane. The center of the soundboard in the region of the lower transversal face brace is obviously going to swell a bit because of the arch in the brace. But what the method calls for is that the neck and the rim be flat. Some provision, however, is going to have to be made on the workboard to account for the swelling of the center of the soundboard--you might break something when you squeeze everything down to the workboard, i.e. when you rope on the back or clamp the sides down.

Now in practical terms you can either raise the neck and soundboard rim from the workboard with a cork/paper shim (like the book shows), allowing the center of the soundboard to clear or "float" above the workboard--or you can dispense with the shim altogether by actually hollowing out the workboard in the swelling region only, allowing the neck shaft and rim to lay flat directly against the workboard.

I chose the shim method for the beginner because it's easier to use a razor and a scissor to make a cork/paper shim than to laboriously and appropriately hollow out the workboard (I use a router and a scraper blade). In the end, however, the hollowed out workboard is superior, but only if you're going to make not just one more guitar, but several.

Given all of this, as much as you try to insure that the neck shaft and the rim of the guitar end up on the same plane after the back is glued on--things happen: the workboard flexes when you rope the back on, things shift minutely. Some builders I know use aluminum workboards or bolt their workboards on top of a massive center beam to avoid any sagging whatsoever. It works for them. The simplest solution for beginners, I believe is to
follow the book's instructions and do the best you can to keep everything on the level during roping, and then after gluing the fingerboard verify that a straightedge down the center of the fingerboard clear the soundboard at the bridge by 3/16" to 1/4" at the saddle location as it says in Procedure /Fretting:/ Step one-Classical Only: Truing the surface/ on page 282. Often just a little bit of extra planing with a sharp plane will correct the
fingerboard slope towards the ideal.

HOW ABOUT FOUR PIECE BACKS?
I bought your book a few years ago, and it was the only book that really helped me build guitars. I am now in the process of making several guitars. I was wondering if you could help me with this one question. I am making a guitar out of cherry wood, I can only find quarter saw wood, and 4" wide. If i glue 4 boards together for the back, would there be any structural weaknesses?

No problem. Some of the greatest guitars ever made, were made with 4+ piece backs. The great Antonio Torres in the last century resawed narrow old Brazilian rosewood table legs for some of his guitars. Just put a small back graft across each seam, along its full length.

 

IS THE NEW NECK BOLT SYSTEM PUT TOGETHER DRY?
On your new bolt in neck system, do you still glue the fingerboard down, or is the entire system put together "dry"?

My new bolt system can hold the neck on entirely without glue, which I have done to string up the unfinished guitar to make tonal adjustments and final evaluation before finishing. But I glue down the fingrboard end at the very end of the process, after the finish is applied and polished, just to insure against any possibility of future rattles.

DO YOU RECOMMEND USING THE NEW SYSTEM ON CLASSICAL GUITARS AS WELL?

The smaller soundhole could make access to the bolts more of a problem, but there is no good reason not to. But there is no reason to, either: the low tension and unlikelihood of the need for a future neck reset makes it unnecessary to change the far simpler, traditional one-piece system. Think of it: the traditional joint consists of two slots. Period. Okay, polishing the finish in the heel-body crevices are a chore. So take your pick.

12-STRING STRUCTURE DESIGN UPGRADE
Although your book has several pictures of 12 string guitars, it never mentions anything extra that may be needed. I tend to play my 12 string more than the 6, so I have an interest in building those. Are there any additional bracing requirements needed on the soundboard for a 12 string guitar?

Just a bridge patch that is about 15% thicker and about a 1/4" wider below the bridge and a top that is about 15% thicker. Everything else the same, except for the dimensional fingerboard and bridge requirements for the additional strings. The traditional problem with 12 strings is that people go nuts beefing up the structure all over the guitar. Most 12 string sets are not twice the tension of 6-string sets, because they usually consists of considerably lighter gauge components, and most people drop the tuning by half a step. Yes, there is always a chance that someone will put on heavy strings and play it up to pitch. They could also drop it on a concrete sidewalk. You could respond to those fears by beefing up the entire structure for no flex whatsoever, but there is a price to pay in the instrument's freedom of response.

TIE BLOCK BRIDGES ON STEEL STRING GUITARS
I've seen some bridges (I think from Takamine) that have no bridge pins. I believe that the strings are threaded through a slot at the back of the bridge. I find this more visually appealing that one with pins in it. However, I couldn't help wondering if this setup would create greater rotational stresses on the bridge? Would the bridge tend to pull more than on one in which the strings go through the soundboard? Would you recommend using that type of bridge at all?

The rotational stresses on the bridge are actually primarily determined by the neck angle (and the consequential saddle height), and not as much on the bridge design. There are no unusual tonal or structural problems with a tieblock bridge to be expected on a steel-string guitar. For my money, the main problem with a tie-block bridge is that it makes setting up and replacing steel strings a bloody nuisance.

 

PROS AND CONS: HEADBLOCK VEE JOINT
You kind of allude to this in the book, but is the V joint still a better (ie stronger) joint than the scarf joint for joining the shaft to the head piece? My woodworking experience tells me it should be. You'd have side grain in the glue joint, as opposed to the scarf joint which is mostly and end-grain to side grain joint. If I made it, I'd be tempted to pin it near the base as well for added mechanical strength. It seems like you only discard it for common use because of the complexity of making it. Is that true?

Due to the strength of modern glues, a well- executed scarf joint is perfectly adequate for the stresses imposed across the steel-string headstock. From a cabinetmaking point of view, a v-joint was technically superior, particularly in the olden days when the glues were less reliable. If you use a v-joint people will shower you with praises for your skill and those in the know will guess that you don't have to make a living at making guitars.

I have a Delta unisaw with the Incra fence system, so I have 1/1000 inch adjustability, and joints like that are pretty routine for me.

Terrific. Then the v-joint is appropriate for your situation.

 

CORAL NUTS AND SADDLES?
While in Grand Cayman, we stopped at "Richards", a jeweler who is world renowned for his work with black coral. I got it in my mind that if you wanted to get fancy on a custom guitar, you could make the nut and saddle out of black coral. I spoke with them about it, and they seemed to think it would work from a manufacturing standpoint. They'd have to do it themselvles of course (it's illegal to export raw black coral) and the cost would be about $150 for the nut alone. This would have to be a very special guitar! What is your opinion on this? The material seems to be at least as hard as bone.

Its remarkable how often I get asked to predict the tonal result of using whatever unusual nut material the questioner can come up with. Folks accord to me powers of prediction beyond that of ordinary mortals. I should be grateful for that consideration, I guess. Well, to tell you the truth, I've never held a piece of black coral in my hand (or even heard of it before) and would only comment that generally, the nut (and saddle) can act as a high-pass filter in very subtle ways, according to their density. Softer materials such as wood will attenuate some of the high frequencies, and harder materials will not, according to a range of densities. Harder materials like brass attenuate few high frequencies, giving a steel-string guitar (what to my taste is) an annoying tonal shine. Where black coral lies on the continuum has to be left for a wealthy experimenter to find out...and then tell me about it.

 

AVAILABILITY OF CARBON FIBER TOPS
Do you have any plans to make your carbon fiber tops available as a product to builders?

Me and my partner in that endeavor, graphite tech Rich Janes, have often talked about it, but just obtaining a sufficient number of tops for my production alone is such a chore that we've put off the plan for the time being. They have to be laid up by hand in the Orient, you know. The answer is yes, we plan to make them available, but when and for how much...you'll just have to stayed tuned.

My most recent prototype yielded magnificent results: a thinline acoustic with a 1/32"-thick graphite top with NO BRACES. The top was so compliant that it yielded some very rich lows, the kind you wouldn't expect from a guitar with 1 1/2"   sides. And startlingly loud and with great sustain. It's been a month and so far, the top has settled into a faint swelling behind the bridge, but nothing to worry about. Yet. I'll keep watching it and let you know.


SETTING THE NECK ANGLE ON THE WORKBOARD
I've glued the back, and somehow the neck and the top are absolutely flat. At least the top on the nut side of the sound hole. On the other side, bridge side, of course the top is about a 1/16th higher because the brace at that general location is arched. I haven't thought about it enough to know if that's a problem or not. I guess I felt unsure of what the of outcome this step would be, primarily because of the shim that was necessary on The workboard in order to accommodate the arched top. I used cardboard, cut from a box, and suspected that it would compress once I wrapped the back. So instead of trying to shim the neck to be at the same level, I let it float above the workboard and trusted that clamping the back at the headblock securely before wrapping would set the proper angle. More than likely I just got lucky. But for future instruments I would like to have a more predictable procedure. I can't lay the sound board on the workboard without the shim because I would risk breaking something, and anyway, the soundboard is no longer flat so it wouldn't do a whole lot of good. I guess the large solid area of the shim provided a level enough surface and enough support for the top, neck and back to be joined at the headblock. If the top and bottom surfaces of the headblock are correct, then I guess the neck angle will be too. Maybe after a couple more guitars I'll begin to understand. Thanks for your help.

You're all right if the neck shaft and the rim of the soundboard exist on a level plane. The center of the soundboard in the region of the lower transversal face brace is obviously going to swell a bit because of the arch in the brace. But what the method calls for is that the neck and the rim be flat. You're also correct in assuming that some provision is going to have to be made on the work board to account for the swelling of the center of the soundboard--you might break something when you squeeze everything down to the workboard, i.e. when you rope on the back or clamp the sides down.

Now in practical terms you can either raise the neck and soundboard rim from the workboard with a cork/paper shim (like the book shows), allowing the center of the soundboard to clear or "float" above the workboard--or you can dispense with the shim altogether by actually hollowing out the workboard in the swelling region only, allowing the neck shaft and rim to lay flat directly against the workboard.

I chose the shim method for the beginner because it's easier to use a razor and a scissor to make a cork/paper shim than to laboriously and appropriately hollow out the workboard (I use a router and a scraper blade). In the end, however, the hollowed out workboard is superior, but only if you're going to make not just one more guitar, but several.


"...THEN I HEARD A CRACKING SOUND!"
Bill, I am building a steel string guitar from your book. I am very slow, what with building jigs and collecting tools, but I am enjoying very much, until now. I was in the process of bracing the top and had the upper transversal graft and finger braces glued on, when I noticed the top was taking on a reverse bow, especially near the area of between the sound hole and the headblock area. I thought I would clamp it down to my workboard to see if it would straighten out easily and when I clamped it, I heard a cracking sound. There is now a split in the soundboard, starting at the headblock end and continuing about 2 1/2 inched toward the soundhole. It didn't split in the glue joint, it split about 1/8 inch to one side of it down a grain line. Of course I am sick, but after getting hold of my self, I have started trying to figure out what to do. Should I try and repair the crack or since I am not so far along with the guitar, Should I just buy new sound board material and start over ? I have tried to glue the crack with the thick super glue, but I'm not sure how well it will hold, since I can't get the glue in the crack very well. Also, I'm afraid the crack will want to travel all the way to the sound hold. Any help or advice you could give me would be appreciated.

P.S. Glad email doesn't show tear stains .

Tut, tut, tut! You failed to heed Uncle Bill's and Uncle Jon's warnings--at your peril! Did you skip TECHNICAL NOTES ON BRACING THE SOUNDBOARD on page 156 to 159? It warns of precisely what happened to you. We toooldd youu soooo!!

I would have said, carve off the upper transversal and that would have freed up the cracked upper portion of the top enough to moisten the wood slightly to have the crack swell and close, so you could reglue it. But you went and gummed it up with superglue (that doesn't work on spruce anyway). So forget that idea.

If the crack will eventually lie under the fingerboard (you said it was in the portion between the headblock and the soundhole), you can hide the repaired top under it. Carve off the upper transversal, scrape off the old glue, rout or saw a straight slot right into the crack, and insert a little strip of matching wood with glue. Then scrape all flush.

But before proceeding to glue the rest of your guitar together, you've GOT to assemble everything in the shortest possible time. Get all the brace blanks prepared, all the blocks, the sides bent and trimmed, the kerfing, the back joined, the back braces prepared and don't do ANY glueing until you have all the parts at hand. Then reserve a long weekend and do the whole glueing/ assembly procedure without having to stop and make the parts or go out and buy stuff.

Time--as you learned--is the enemy here.

 

GUITAR KIT BOO BOO
I found a little boo-boo on my Guitar kit - it appears that Martin didn't give me enough material for the soundhole braces (and I'm like halfway through now so I'm got quite peeved!). I just cannot get spruce where I am now so I bought some balsa wood and shaved it down to thickness. Before I paste it down can I get an opinion from you? And since I'm at this, I found that after cutting the back of the guitar to shape I have enough material to cut out a bridge patch. The kit came with a maple bridge patch, so my question is, is a Rosewood bridge patch better or should I not bother.

Forget about balsa. You might as well use styrofoam. Try any available hardwood you can get into strips.

The difference between rosewood and maple bridge patches are slight. You get a slightly glassier edge with rosewood, a little smoother sound with maple. But the effect/difference is quite marginal.

 

WHY TAPE UP THE DOUBLE ROD?
In your book you write that the truss-rod should be wrapped with metal tape, but here in Holland nobody seems to know it even exists. What they do have is aluminum tape but i am wondering if its strong enough for the job.

The tape is for holding the two rods firmly together so they won't rattle against each other. Any tape will do, except that paper or masking tape tends to dry up and shrink up over time, and the metallic tape won't. So you can use any type of metallic tape. The tape I use here is sold in hardware stores, has a metal foil surface on one side and a paper surface on the other which peels off and reveals the stickum.


NECK SCULPTING
In your narrative on neck sculpting you say that the your neck design is an apex with a peak that is slightly of center. Could you elaborate on this? In particular is the center moved to the treble or bass side of the neck. I am guessing you would want to move it to the treble side a bit, but don't have clue why.

If you look at your hand you'll notice that the unsymmetrical pocket where you cradle your neck, between your thumb and index finger is something like the shape the neck should be. This is really only for players who cradle the neck in their palm, rather than play classical style with the thumb tip on the centerline of the shaft. In that case, a flatter shaft centerline is more comfortable. Hope that helps.

 

COPYING A GUITAR
I have a desire to build a guitar similar to a Martin 000-28S. Because I will be constructing this from a kit I will have to opt for the only kit design largest enough: D-28. I realize that there will be many modifications in building the 000-28S from a different kit. Therefore, I have a few questions:

1. Where I can obtain a blue-print for a 000-28S ?

You got me there. I know of none. I'm thinking of preparing a series of blueprints of all those guitars (I use to be a draftsman thirty years ago), but I've got to many projects open as is. But it'll happen before long.

Find one and measure it. You can get the brace pattern by "candling" the top: putting the guitar into a darkened room with a light bulb on a wire inside the soundhole. All the braces will shine through the top as if  the top was transparent.

2. Will the materials provided in the D-28 be adequate (ie., large enough) and just require modification to the 000-28S ?

The D28 is much larger than the 00028 so you'll have stuff to spare.

3. Do you know of any literature out there for constructing a 000-28S, or similar size, guitar ?

You can borrow my book from the library which essentially describes the making of a larger Martin M guitar. It tells you how to extrapolate all the dimensions for a smaller guitar during the design and layout phase.

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