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Thread: Hybrid X Lattice

  1. #1

    Default Hybrid X Lattice

    Hi all.
    I am in the early stages of designing a guitar bodied bouzouki and thinking about the bracing.
    Iím thinking of using an adaptation of the x-lattice in Graham McDonalds Bouzouki Book for the flat topped instrument.
    My question is regarding potentially half lapping the lattice below the X.
    In the book, he suggests cutting shorter braces to fill in the gaps between braces rather than half lapping all the lattice. Obviously Graham and many more people since have made fine instruments using this technique, and I wouldnít assume to question that for one moment.
    But I am wondering if anybody here goes to the trouble of lapping the lattice as well as the X brace or whether it really is unnecessary. Iím thinking of making the lattice off the guitar and sanding the required radius in a dish before gluing to the soundboard.
    Any thoughts or experiences greatly welcomed.
    Thanks
    Last edited by Orra; Sep-23-2022 at 3:58am. Reason: Spelling

  2. #2
    Registered User sunburst's Avatar
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    Default Re: Hybrid X Lattice

    I think the lack of responses may be that many, like me, don't understand the question.
    I don't have Graham's book, and when you say lattice I think of Smallman lattice.
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    I have no experience with lattice bracing and probably wouldn't have anything useful to contribute anyway, but some clarification of the question might help you get some info from someone.

  3. #3
    Fingertips of leather Bill McCall's Avatar
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    Default Re: Hybrid X Lattice

    I would think fitting and installing the lattice as one piece would be a much more difficult process than installing individual pieces. Of course you could install all of the pieces of one side and then let in all of the cross pieces, which I also think would be quite tedious. I donít know what the benefit of either method would be. If the goal is added to stiffness perhaps a slightly thicker top is an easier way to get there.

  4. #4
    Teacher, repair person
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    Default Re: Hybrid X Lattice

    I have no opinion on the lapping question.

    I do have an opinion on lattice braced steel string guitars, since I've had a couple go across my workbench.
    My experience has been that they are prone to developing problems, and are difficult to repair.

    If you decide to proceed, I recommend that you use a method that provides the most accurate fit, and strive for perfection in your glue joints. If something pops loose later, it won't be any fun trying to repair it through the soundhole.

  5. #5
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    Default Re: Hybrid X Lattice

    There are a few. physical considerations that might shed some light on this for the op. First, a thicker top plate will result in greater stiffness all right, but that stiffness will come at a cost of greater mass. And that mass is exactly what lattice bracing systems were original designed to avoid. Bracing in general increases stiffness while barely increasing mass. Second, wood is anisotropic (actually orthotropic), meaning that the stiffness is different in different directions. The cross-grain stiffness is much lower perpendicular to the grain than it is parallel to the grain lines, usually by a factor of anywhere from 7x to nearly 30x. Bracing generally has much less effect on the stiffness parallel to the grain than it does on the stiffness across the grain. Piano soundboards are similarly anisotropic, but the "ladder" bracing makes the soundboard just about isotropic overall (unless the soundboard is made of plywood, in which case it is closer to isotropic to begin with). In mandolin family instruments and arch top guitars, the "parallel" braces which are mostly oriented along the grain lines don't raise the frequencies of the lower plate modes much, if any. They do serve to distribute the the static down force from the strings over the bridge though. Otoh, ladder-type bracing, such as in Neapolitan mandolins and lutes, raises the overall flexural stiffness of the top plate a lot. The lowest plate mode in a Neapolitan (aka bowl back) mandolin occurs at 500 Hz or above, compared to around 250-300 Hz for a typical arch top ff-hole mandolin. So the orientation of the baking pattern matters a lot more than do specific details of brace placement and shaping. Lattice bracing patterns, like ladder-type bracing, have their greatest effect on the perpendicular stiffness of a plate, so they raise modal frequencies more, but at a cost of less mass overall.

    One thing you might want to know about your plate before you consider bracing patterns is what the parallel and perpendicular Youngs moduli (aka MOE) are. You can make approximate measurements of those moduli yourself. James Blylie had an article a few years back in American Lutherie on determining the parallel MOE in woods. You can modify his method just a little to measure the approximate perpendicular MOE as well. I can't find the reference at the moment, will have to look it up. But you can easily look it up on the GAL website (luth.org). Graham Caldersmith found in the mid-1970s that the overall flexural stiffness of a plate varies with density as the square root of the product of of the parallel and perpendicular moduli.

    After all that, I can finally address your question about box joints vs short pieces. I don't think it makes a huge difference, so I would advise doing it the way that works for you. The reason for that is that whether you butt short pieces of wood together or use box joints, the forces from the strings via the bridge just "see" an impedance based on how much brace wood is glued to the plate and what its orientation is with respect to the grain direction. Whether with box joints or with butt joints, the same overall bracing pattern will have pretty much the same effect of the overall stiffness of the plate. Tiny gaps or breaks do not have a hinging effect. Iow, more bracing means more stiffness, other things being equal. That's probably what lead Graham to do it the way he did.

  6. The following members say thank you to Dave Cohen for this post:


  7. #6
    Mandolin tragic Graham McDonald's Avatar
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    Default Re: Hybrid X Lattice

    There are. couple of different ways you can approach this. My suggested brace size is 3 x 6mm (1/8" x 1/4") spruce. You can make a fully lap joint lattice beforehand, but they are quite flexible and fragile. If you want to sand a arch into the lattice, you will really need to make up a form of 3mm slots to make up the lattice so you can hold it firmly for the shaping. At the same time it is not really necessary. If the main X braces put in the slight doming you want for the soundboard and you are using a dished board to glue the braces a go-bar deck and some flat cauls which spread over a couple of strips at a time will happily force the lattice into the slight done. The edges can then be tapered down once glued.

    An alternative to the fully lapped lattice is to use 3x3mm strips in one direction, so slots have to only be cut in half the strips. What I have been doing for a while (not that I make many bouzoukis these days) is to glue in the full length strips in one direction and cut short lengths to fit between the long strips. It doesn't take too much time to cut the little strips and fit them. If Dave C says it won't make much difference from a physics point of view, believe him!

    One thing to remember, this was a bracing pattern developed for fixed, pin bridges, not floating bridges with a tailpiece. It is not going to work for resisting the downwards pressure from the bridge and compressional forces from the tailpiece. I know there are those who claim that fixed bridge bouzoukis/OMs just sound like 2/3 of a 12 string guitar, but there is something about the quick attack and separation of the notes which the lattice brings (I think) to the sound which distinguishes this style of bracing.

    Cheers

  8. #7

    Default Re: Hybrid X Lattice

    Hi and thanks to all.
    I wrote a long reply addressing each of you, but slowly over the course of a day as Iím a single parent of a 2 and 4 year old, both currently ill.
    By the time I clicked to post it I had been logged out and the back button took me to an empty message box!🤬
    It was all a great help, I got the answers I had hoped for and more.
    I will hopefully rewrite soon, havenít managed to find the time so felt I needed just to write a short thanks so as not to come across ungrateful

  9. #8
    Mandolin tragic Graham McDonald's Avatar
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    Default Re: Hybrid X Lattice

    I am always happy to answer questions directly. Just drop me an email.

    Good luck and I look forward to seeing some pics of the finished instrument.

    Hope the children get better soon.

    Cheers

  10. #9

    Default Re: Hybrid X Lattice

    Thanks Graham.
    They got better by passing it onto me instead!
    Pretty standard.
    Might be a while for that particular instrument, have at least 3 in line before that one.
    Hereís a few shots of what Iím currently working on. Itís the prototype for my first commission, a tenor guitar going to Finland. (If I can work out how to post photos?)ÖÖ..

  11. #10

    Default Re: Hybrid X Lattice

    Not a mando family admittedly, but possibly of interest as next up in my bench is an all walnut octave mandolin based on the same guitar body shape.
    Canít work out how to post pics though unfortunately

  12. #11
    Mandolin tragic Graham McDonald's Avatar
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    Default Re: Hybrid X Lattice

    Posting pics is a bit clunky but it does work once you get the hang of it. There is probably some step by step instructions somewhere on the forum, but the simple version is to click on the little icon in the menu bar above where you type your reply that looks like a square frame. That will open a little pop up window where you can go to the folder where you have the photo you want to upload and click on that. The name of your file appears next to the "select file" button and underneath that are clickable words "upload file" and then some html code appears wherever you left the cursor on the message window. A thumbnail appears when you post the reply.

  13. #12

    Default Re: Hybrid X Lattice

    Hmm
    I donít seem to have the square window?
    Iíll do some more looking. All I could find was some apparently outdated info regarding clicking in a paper clip icon
    Not sure if itís because Iím on a phone instead of a computer? Sometimes mobile sites are slightly different

    Old dogs and new tricks

  14. #13
    Mandolin tragic Graham McDonald's Avatar
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    Default Re: Hybrid X Lattice

    A screen shot of the reply screen, with the necessary icon circled 8-) Mind you, I do this on a desktop Mac and have no idea how it might look or work on a phone.

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  15. #14

    Default Re: Hybrid X Lattice

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  16. #15

    Default Re: Hybrid X Lattice

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  17. #16

    Default Re: Hybrid X Lattice

    So, on a mobile if you scroll all he way down to the bottom of the chat there is a link for ‘full site’
    If you click on that it brings up all the icons in your screenshot. I had a feeling that the mobile phone would have something to do with it.
    Not sure why the photos are rotated 90 degrees though. I think I’ll live with that for the time being.
    I haven’t gone to town on rosette/purfling etc as jut a prototype that I’ll be keeping for my own use, although I’m increasingly of the less is more attitude to decoration

  18. #17

    Default Re: Hybrid X Lattice

    In fact Graham, out of interest, it is through this commission that I finally bought your book after having it in my sights for some time. I had bought a set of bog oak a while back for this shape that I was going to use, only to find out the ribs were much shorter than ordered and not long enough. So that set has now been designated for a flat back bouzouki, again for myself. Can’t say I’m complaining.

  19. #18

    Default Re: Hybrid X Lattice

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