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Thread: top deflection

  1. #1
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    Default top deflection

    Hi everyone, I now have my 2 first mandolin builds constructed in the white. One is an F5 with an Engleman top and the other an A5 with a European spruce top.
    I don't want to get too much into the technicalities of tuning the plates or top deflection, but after checking the tops on these builds by hand pressure, I can detect the deflection on the F5(engleman), but the A5 seems very stiff and barely moves.
    I carved them pretty much the same in terms of target graduations etc, so the general thicknesses will be very similar.
    How much deflection should I notice by hand, if any at all? How will this affect the instruments?
    Do I accept that the stiffer top will just sound different and maybe brighter, or maybe take down the recurve a bit more until I can feel more movement?
    These are my first builds so I'm not trying to make them sound like Loars or anything else, but at the end of the day they sound like a mandolin, then I'll be happy.
    Thanks Mike.

  2. #2
    Registered User fscotte's Avatar
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    Default Re: top deflection

    I think some builders squeeze the plates but I'm not sure they do that to measure any amount of deflection.

    For consistent builds you'll need to build a deflection jig. After several builds you will start to zero in on what deflection numbers are good for you.

    F'instance, I make my tops around .022 average. That's a very tiny amount of movement, and the tonal difference can change rapidly as you move from that target.

    So, build a device, then find yourself a real fine sounding mando, measure it's deflection, and you can use those numbers as a reference.

  3. #3
    Registered User keme's Avatar
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    Default Re: top deflection

    Just a side note:
    I recall reading in the Frets magazine (somewhere, sometime in another century) an article by a luthier who quoted one of his masters' criticism of his work, to the effect that "you don't clamp the top to the brace, you clamp the brace to the top." In other words: when glueing there should be no flex (tension) in the top, only in the brace.

    I am pretty sure that said article was about mandolin construction.

    Just something I had forgotten, which sprang to mind when I read this discussion on the subject of flex. This may be obvious to everyone, or it may be just stupid and old school. I don't know. Surely, most of you will know more about this than I do, but sometimes it makes sense to state the obvious and only a fool would dare it.

  4. #4
    Registered User sunburst's Avatar
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    Default Re: top deflection

    When you finish these two, see if they sound different and if they do, and one sounds better to you than the other, that might mean that you want to continue with similar deflection in your tops. Someone else might prefer the sound of the other one though...
    Also, it depends on the density and total mass of the tops, and it depends on the stiffness and density of the backs that they are paired with.

    In short, you are at the beginning of a journey that involves building mandolins and keeping good notes whether mental of physical. We learn from what we do that seems to work and from what we do that doesn't seem to work. Fortunately, we have plenty of info to be able to build successful mandolins, so following a proven model; "doing what everyone else does"; is the starting point.

    You can build a deflection jig if you'd like, it can help with consistency later, but for now it will only help with you accumulation of knowledge of what works by helping you keep more accurate records. In other words, you have no target deflection yet for top and back plates, so you don't know what to shoot for. That will come later.

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  6. #5
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    Default Re: top deflection

    Thanks for the replies. Like I said, I don't want to get into deflection jigs and technicalities, at the moment. I guess what I'm asking is whether it is possible to have no discernible deflection when applying had pressure to the top of a boxed up mandolin, and yet it could still sound ok when finished. I'm not trying to measure deflection, but to determine whether it needs to be visible when pressed by hand.
    thanks again, Mike.

  7. #6
    Registered User sunburst's Avatar
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    Default Re: top deflection

    Quote Originally Posted by mikeyb2 View Post
    ...I guess what I'm asking is whether it is possible to have no discernible deflection when applying had pressure to the top of a boxed up mandolin, and yet it could still sound ok when finished...
    I'd say yes it is absolutely possible.
    If you follow a proven model, and your work is all done at least OK so that the structure and geometry are acceptable, you will end up with something that I can guarantee will sound just like a mandolin.
    If you do everything to a high degree of excellence, it will sound just like a mandolin.
    No other guarantees until you have more experience to draw upon.

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  9. #7
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    Default Re: top deflection

    Quote Originally Posted by sunburst View Post
    I'd say yes it is absolutely possible.
    If you follow a proven model, and your work is all done at least OK so that the structure and geometry are acceptable, you will end up with something that I can guarantee will sound just like a mandolin.
    If you do everything to a high degree of excellence, it will sound just like a mandolin.
    No other guarantees until you have more experience to draw upon.
    Thanks John, that's encouraging. I'll continue and keep my fingers crossed. I like to think I've done a reasonable job so far and dimensioned the plates close to the figures advised by you and others on my earlier posts. Like you mentioned earlier, it's a learning curve but I am taking it all in as I go along( well as much as my old grey matter will allow!)
    cheers Mike.

  10. #8
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    Default Re: top deflection

    The fact you have two mandolins that are different is a great opportunity to learn something that might be very useful for future builds. If they were exactly the same, you would learn nothing, so it is good they are different. And, the stiffer top won't necessarily sound brighter. You will only find out if it does when the strings are on.
    Peter Coombe - mandolins, mandolas and guitars
    http://www.petercoombe.com

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