Mahogany 00 acoustic guitar

Discussion in 'Tele Home Depot' started by Freeman Keller, Aug 7, 2019.

  1. Freeman Keller

    Freeman Keller Tele-Afflicted

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    Ripped some spruce into 5/16 stock for braces. Sanded the 15 foot radius into four of them to be back braces

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    Notched he center reinforcement and glued a couple of braces in place

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  2. otterhound

    otterhound Poster Extraordinaire

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    Since there are those here that do not know , please describe the grain orientation in the neck and tail blocks .
     
  3. Freeman Keller

    Freeman Keller Tele-Afflicted

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    Most builders orient the grain in the same direction as the side grain is running. The argument that I heard is that you want the expansion coefficients to be the same as the sides and the neck.

    IMG_0950.JPG
     
    Last edited: Aug 11, 2019
  4. Freeman Keller

    Freeman Keller Tele-Afflicted

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    Speaking of the neck, time for a little carving. I use sort of a simple facet approach but I'm not anal about it - I don't measure or anything like that. I just start shaving some angles off the neck stick until it looks about right, then shift and take some more off. At the same time I'm working on the shape of the heel and the head transition and that little dart thing

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    At some point in the process I start using some little templates taken from a neck I know I like.

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    My basic philosophy for carving a neck is to take a hunk of mahogany and remove every thing that doesn't feel like a neck.
     
  5. David Barnett

    David Barnett Doctor of Teleocity

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    What's under the cover? Looks kinda like a big Healey?
     
  6. Freeman Keller

    Freeman Keller Tele-Afflicted

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    I wish. Its just a '63 Morgan Plus 4. Don't look behind the curtain, Dorthy.
     
  7. otterhound

    otterhound Poster Extraordinaire

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    The little dart thing is called a volute . It is a holdover from the days when necks were made from 2 pieces . At least , that is in reference to CF Martin . It's purpose was/is strength at a weakest point .
     
  8. Freeman Keller

    Freeman Keller Tele-Afflicted

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    Thank you. I believe I mentioned that in post #16
     
  9. Freeman Keller

    Freeman Keller Tele-Afflicted

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    Its the next day. I glued two more braces on to the back and some little sticks on the sides to try to prevent the dreaded key crack.

    IMG_0982.JPG
     
  10. Freeman Keller

    Freeman Keller Tele-Afflicted

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    While glue is drying again I'm going to take one panel and just talk a little bit about acoustic guitars and how they are made and maybe how they are different from telecasters.

    All guitars make sound by moving air molecules that impinge on the listeners ears. Telecasters do it (mostly) by the ferrous strings moving thru a magnetic field generating an electrical current that eventually moves a loud speaker cone. Acoustic guitars do it by moving the top (mostly) which moves air - some of it off the surface of the top but most pumped in and out of the sound hole. The top of an acoustic guitar moves in very complex ways - an incredible amount of research and study has attempted to understand it. Its important to consider that the top doesn't just move up and down but some parts might be going up while others down, sometimes it seems to be rocking.

    We can divide the way the strings pass over the bridge and are anchored into two different designs - they respond differently to vibration and the top moves differently. The first is what is sometimes called a "floating bridge" - used on bowed instruments (violins), archtop guitars, resonators, gypsy jazz guitars (SelMacs), mandolins - almost any instrument with a tail piece. On these instruments the string tension is anchored at the tail piece, there is a strong vertical component of tension directly into the top (that is what holds the bridge on and keeps if from tilting forward or backward). Its pretty easy to calculate the downward component if you know the break over angle and the string tension. Here is a pretty typical acoustic archtop guitar. With a normal set of light gauge strings there is about 65 pounds of down force pushing the bridge into the top.

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    When the strings on this kind of guitar are plucked most of the energy is a vertical component moving the top up and down.

    Classical guitars and steel string guitar with pinned bridges are called "fixed bridge" guitars - the bridges are glued onto the top and the strings terminate somehow at the bridge - either tied around the back part or stuck thru holes in the top and held in place by pins. Here is a classical tie block

    IMG_4778.JPG

    Here is a typical pinned bridge on a steel string guitar - the ball ends of the strings are pulled up against the underside of the top and held in place by slots in either the pins or bridge - a slight wedging action holds the pins in place.

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    The important thing is that with fixed bridges the string forces at the bridge are resolved into different components that the floating bridge. There is a downward component at the saddle, an upward component at the balls, a rotational component around the front of the bridge and a shear component along the glue line. The net result is that the top is pulled up behind the bridge and pushed down in front of it. When the string is plucked the top both moves up and down but also rocks around that axis of the front of the bridge.

    The builder of an acoustic guitar has a fine balancing act - she needs to make the structure of the guitar light enough to easily move at all of the frequencies it will be asked to generate, yet it must be strong enough to not explode under the string tension which is resolved into all those different components. A classical guitar might have 100 pounds of tension (about the same as a tele with 10's), a steel string guitar might be 170 or so pounds, and a 12 string might be 230. Think about that for a second - those are the weights of a skinny person or an average person or a pretty heavy person, all hanging from that little 1 by 5 inch piece of wood called a bridge.

    There are lots of variations on these two bridge configurations but most acoustic guitars will fall into one or the other. There have been many scholarly studies made of the forces on bridge and their actions when excited by moving strings - it is highly complex and the math can be somewhat overwhelming. I would point the reader to Mark French's books Engineering the Guitar and Technology of the Guitar.

    If all you have is the vertical component of a floating bridge (remember the actual tension is anchored to the end block thru the tailpiece) then a variety of bracing will do. A simple X brace like many archtops, a couple of tone bars like a mandolin or a violin, or a few cross braces forming a ladder will support that force nicely. Many of the best old guitars were ladder braced with tail pieces. Here is my version of an old ladder braced twelve string - the braces are pretty thick to support the down force

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    (by the way, almost all acoustics have ladder braced backs altho a few modern builders are doing some wacky things with back bracing in the theory that it will improve the backs contribution to the sound)

    When we use a fixed bridge we now have to contend with that rotational force. If the tension isn't too high a lightweight configuration of small braces works very well. The traditional fan brace and all of its variations have worked for classical guitar for hundreds of years. Here is a Torres style 7 fan from the classical 1937 Hauser that everyone builds as their first nylon string guitar

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    Lots of things going on here - we could spend pages discussing them. I just wanted to show the configuration.

    Last, but far from least, is the bracing design that CF Martin came up with way back in the 1800's. In my opinion it is pure genius. Martin put two main braces in an X configuration with the crossing point between the bridge and the sound hole

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    That is the weakest part of the top and is under the greatest force from the rotation of the bridge, so thats where the strongest part of the brace is located. The braces are at their maximum height in that spot and the crossing makes it even stronger. The X fans out across the lower bout with the wings of the bridge sitting right over the top of the legs. That means the bridge is driving energy into the X and thus into the top. The maple bridge plate is both a brace but also a hard surface for the balls to be anchored against. The two angled braces below the bridge plate provide cross grain reinforcement for the spruce top but also by their shape and size help to shape the bass and treble tones.

    By removing wood from selected areas of the braces they can be made weaker and thus more flexible. Like everything else, there are lots of ways to do this but Mr Martin's time honored way is pretty hard to beat.

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    You will find that everyone who builds acoustic guitars has their own take on what kind of bracing to use, how strong or weak it needs to be, how to walk that line between strength and movement. There are many many new bracing schemes coming out every day - I'm not smart enough to understand many of them so I stick to the time honored and proven X bracing shown above.

    You'll get a lot more chance to see this come into being but I wanted to provide a bit of back ground.
     
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  11. Freeman Keller

    Freeman Keller Tele-Afflicted

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    While I was talking about different bracing designs I thought I would show a couple of pictures of the three traditional neck attachments. First is the so called "Spanish heel" used in classical guitars. Nylon strings exert about 100 pounds of tension, most classicals don't need truss rods (altho a few have them). The neck block is part of the heel and slots are cut into it to receive the sides

    08.jpg

    Spanish heels are strong, the geometry is built into the guitar and can't be easily changed. That is normally not a problem - classical guitars rarely need to have their necks reset.

    The time honored neck joint for steel string guitars is the dovetail. It is an elegant wood working joint where as the tenon is seated into the neck block it pulls the cheeks against the body and tightens itself. Properly done it doesn't even need glue to hold itself together.

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    Dovetails have a big advantage over Spanish heels in that they can be taken apart if the correct glues are used. The geometry of most acoustic guitars will change over the years and it is frequently necessary to "reset" the necks - that can be accomplished with dovetail joints.

    However dovetails are just plain a pain. I did dovetails on my first few guitars to try to learn how - it was frustrating as hell. I still do them on guitars like the one posted where I can't get inside the box to access hardware, but most of the time now I use something else.

    That something is the bolted M&T joint - a simple straight tenon sticking into the neck block with a couple of machine bolts holding it in place.

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    You'll see more of this as the 00 goes on.
     
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  12. Freeman Keller

    Freeman Keller Tele-Afflicted

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    I'm going to do one more little lecture in the Acoustic Guitar 101 Theory class. I'm sorry if its boring - we'll get to the exciting subject of brace shaving in a minute.

    However, did you know that flat top guitars don't have flat tops? Or backs? We've already encountered that with the back, but its really important for the top. Guitars are built with a very small but still significant dome to the tops and backs. Think about a sphere 50 feet in diameter - that is the amount the top is domed. For the back think about a dome 30 feet in diameter - that is pretty common.

    There are two reasons for the dome - first, a dome is a very strong structure, much more than just a flat sheet of spruce or mahogany. Brick arches support themselves without any mortar - it wants to resist downward forces trying to flatten it out. But the second reason is even more important - doming the top and back gives it the ability to resist changes in humidity.

    Wood for guitars is dried, either in a kiln or in air or both, then often left to stabilize with respect to its surroundings. My wood stash is in a corner of my wine cellar which stays 45% RH and 45 degrees F year around. I keep my shop between 35 and 50%, if the RH drops below that I put the wood away and don't build. I also try to keep my house at 40 or 45% RH, my music room has a little humidifier and all my guitars are stored in their cases with a humidifier unless I'm playing one.

    40 or 45% is comfortable for me and for my guitars. Much above that is unpleasant, but probably not too harmful (living on a boat in the Bahamas might be a different story, but alas, I don't have to worry about that). However when the RH drops below 35% my skin gets flaky and itchy, and the wood on my guitars shrinks.

    One of the first indications of a dry guitar is that the fretboard shrinks and the frets don't, so they stick out of the ends of their slots. Not much but enough that you can feel the sharp ends. Most people will just dress them back and go on playing. But with a acoustic several other things happen. The finish gets all wonky looking with little ridges running the direction of the grain, and worst thing, the top shrinks.

    If the top were flat and attached to the rim at its edges, the shrinkage would simply mean that something will give - it cracks, usually along the center seam since that is such a small glue area but it could be anywhere it the wood itself. I can't tell you how many cracked guitars I see each winter - when the heat is on in our houses we are drying the air and the RH is frequently 15 or 20 percent and guitars crack. I once actually HEARD a guitar top cracking. It was a painful lesson.

    If the top is made with a dome in it the first thing that happens as the wood gets dry is the dome drops - sooner or later the guitar will become flat. Left to continue to dry out it will eventually crack, but the dome buys you some time. You'll notice the action going down, the guitar might get buzzy, some people will want a new saddle and setup. When I see this I hydrate the hell out of it.

    OK, so a little dome is good, almost all acoustic guitars have it (or should), we will build ours with a 25 foot radius in the top and 15 in the back - these are more or less Martins standards.
     
  13. Freeman Keller

    Freeman Keller Tele-Afflicted

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    We've already sanded the back braces at the 15 foot radius and glue them in using a radius dish, I don't have the correct dish for the top so I just made some 25 foot clamping cauls/sanding blocks.

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    Once the braces are shaped on the glue surface I just glue them in using the 25 foot radius as a caul

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    The sound hole makes it convenient to get clamps in place - I just do one brace at a time with the caul. BTW, the big brace above the sound hole, called the Upper Transverse Brace (UTB) is also sanded to the 25 foot radius - the top is domed from side to side and front to back).

    I'll put this away until tomorrow.
     
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  14. Freeman Keller

    Freeman Keller Tele-Afflicted

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    Glue has dried on one side of the X, notched the other and fit it in place

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    The angle is a bit wider than 90 degrees so the notch need to be carefully fit. As before its clamped against the 15 foot caul - if I had a radius dish I could do all the braces at once in the go-bar deck. (There is a trick I could use without the dish but this is just as easy)

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    The top brace across the upper bout is the infamous "popsicle brace". Prewar Martings didn't have it, post war ones do, so of course that is one of the things people talk about when they try to recreate the vintage sound. There are even a few folks who remove them from post war guitars. The purpose, along with the UTB is to keep the fretboard extension from diving thru the upper bout as string tension pulls the neck back. I put them in because I think the theory is valid - I also don't believe the upper bout is all that active in sound creation.
     
  15. teletimetx

    teletimetx Doctor of Teleocity

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    thanks for all the photos and the explanations. It's much appreciated.
     
  16. E-miel

    E-miel TDPRI Member

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    Great thread mister Keller. Always thought building an acoustic wasn't going to happen for me, reading this lets me think one day I might be able to pull it off. You're a great inspiration and it is very kind of you to share your knowledge on this forum.
     
  17. Freeman Keller

    Freeman Keller Tele-Afflicted

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    My goal here is to inspire my young friend and give him a general idea of what he is getting into. The other thing to remember is that there are lots of ways to get around the really tricky parts - for many people including my first a kit makes all kinds of sense. Many kit suppliers (LMII, Blues Creek) will customize what you get for your needs - don't want to bend the sides, they'll do it for you. The other possibility is to find someone like me who will help you thru the tricky parts - I told my friend that I will NOT build the guitar for him and he is NOT free to just come over and use my shop but that I would help him with those operations that may be troubling - like bending sides.

    There are also some great lutherie schools where you can build one or more guitars under the guidance of an experienced builder - expensive, yes, but the results will be good. You have some resources in the EU that we don't have here, particularly if you want to build a classical style guitar. Some American luthiers come to Europe to train under a Master builder - very much a tradition in guitar building.
     
    Last edited: Aug 13, 2019
  18. Freeman Keller

    Freeman Keller Tele-Afflicted

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    E-miel, I know that many of the products and sources that I use won't be available to you, but there must be others. I'll refer to the ones I know (LMII for example) but I also know they can't ship to Europe. Heck, we have that problem right here in North America - its difficult for someone living in Canada to get the same woods and materials as I can get. I believe in CITES but it certainly creates some problems.
     
  19. Mr_Q

    Mr_Q Tele-Meister

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    Can you summarize how you made the 25' radius cauls? I'm envisioning 25' of string and a pencil...
     
  20. Freeman Keller

    Freeman Keller Tele-Afflicted

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    I cheated. In my previous life I was an engineer at a fab shop. We had a lot of really cool computer controlled machines - mills, turning centers (cnc lathes) and a big old metal cutting laser. I had access to these tools on my lunch hour and while I never did use them to make any guitar parts (well, a few for a resonator) I made all kinds of jigs and fixtures. For the radius caul I simply drew it full scale in 2D CAD and sent it out to the laser.

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    (there is no pun intended with the brand of the laser)

    Once the metal template was cut out I traced it onto wood and made my cauls

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    The 25 foot of string and pencil would have been my second choice.
     
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