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Thread: Bracing for flat top mandolins

  1. #1

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    hello.

    i would be grateful for some information and advice.

    i have built a couple of kit instruments and now want to build a mandolin from scratch. i play mostly irish music, and want to build a flat top instrument.

    please can someone suggest/explain some bracing types for flattish topped instruments with slight induced arch.

    also, what kind of wood is generally used in bracing struts/bars?

    thank you very much.

    FT

  2. #2
    Registered User Bill Snyder's Avatar
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    Get the Troughton book Mandolin-Manual-Craft-Science-Mandola. It should give you the information you need and it has plans.
    Bill Snyder

  3. #3

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    thank you, Bill. that looks really good. i'll very likely order one come payday.

    until i get myself sorted with proper reference material, has anyone any more input?

    i appreciate the help.

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    There's also "The Bouzouki Book" by Graham McDonald. Although it's primarily concerned with bouzoukis (obviously), it's all relevant to mandolins too. It also comes with plans that could be altered to fit a mandolin body/neck size.

    IIRC, Troughton uses lateral braces with a floating bridge, but McDonald uses a lattice based on a X-brace, and recommends a fixed, guitar-style bridge.

    Patrick

  5. #5

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    I like Graham McDonald's bouzouki book over Troughton's book. I think it is written more for the layperson. Also, Don Kawalek offers plans and instructions on building a flattop.

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  7. #6
    Registered User otterly2k's Avatar
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    FYI, Don's kits do have a slight induced arch for structural strength.
    Karen Escovitz
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    Spruce or cedar for the X-brace.

    Cross between the soundhole & the bridge with the feet of the bridge sitting on the braces at they open towards the body of the mando

    this is a guitar shaped one but it'll give you the idea.......
    Quote Originally Posted by stout1
    Now, thanks to Martin and his guitar shaped mandola, I have been stricken with GBMAS, guitar body mandola acqusition syndrome
    hey!! I got my own Syndrome!!!!

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    FYI... The Troughton book uses the spanish construction method where the sides are attached in slots to the neck/neck block.

  10. #9
    Mandolin tragic Graham McDonald's Avatar
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    Thank you for the kind words about The Bouzouki Book 8-)

    I have never tried a pin bridge on a mandolin. I know Ovation make them, but they look funny.

    I think the main problem with flat top mandolins is the tendency for the soundboards to buckle around the soundhole, mainly from lengthways compression. I have been fooling around with this kind of H bracing using a 15' radius arch. The soundboard has a dome shape, and the lengthways curve sets the neck back at about the right angle for a 10-12mm (3/8-1/2") bridge. I suspect the long arms of the H can be made quite light as it is a lot of lengthways compressional force on them, but I don't know how light yet. The ones in the pic are around 3/16" wide x 1/2" high. Feel free to play around with the idea.

    cheers



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  11. #10

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    thanks for the recommendations for further research material, guys. special thanks to Martin and Graham for posting those pics.

    this is all very helpful stuff and i'm grateful for your time and patience.

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    Quote Originally Posted by
    the main problem with flat top mandolins is the tendency for the soundboards to buckle around the soundhole, mainly from lengthways compression
    Graham - Wouldn't an X-brace configuration also serve to take up some of the longitudinal strain?

  13. #12
    Mandolin tragic Graham McDonald's Avatar
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    The tension on a flat-top floating bridge instrument is coming from the tailpiece and the neck wanting to rotate, with the strings essentially trying to push the bridge down. I don't think an X brace is doing much to offset that compression at the tail block and to stop the neck block wanting to rotate while It will certainly be doing a reasonable job holding up the middle of the soundboard under the bridge. At the very least any flat-top instrument needs support from the neck block down around the soundhole which is the weakest part of the structure.

    Basicly I think a flattop/floating bridge instrument is the least structuraly sound way you can build a mandolin. There has to be compromises between structural strength and a freedom for the soundboard to vibrate. At the same time building an instrument like this is a good simple introduction to the art and as long as you can build in that equilibrium of strength/resonance, you can have a enjoyable and playable instrument. The H brace idea is one approach to this.

    cheers

    graham

  14. #13

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    Graham, in your image above of the 'H' type bracing, how does one deal with the points where the struts cross each other? this is something i've never had a close look at. the instruments i built either had tone bars that didn't make contact, or bracing patterns that didn't involve the struts crossing over. i'd be very grateful for a bit of info' on that.

    also, it looks like you have kind of wooden "feet" on the end of your braces. is that right or an illusion?

    thanks very much.

  15. #14
    Mandolin tragic Graham McDonald's Avatar
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    The braces are just notched in the same way you would notch an X brace - halfway though both. I think I notched the 'up' side of the transverse brace and fitted the two lontitudinal braces over that. The little feet are to tie the braces into the sides more effectively. Old style classical guitar builders often do this with the main transverse braces on the soundboard.

    There is another thread on bridge and brace positions which has an interesting diagram of a Selmer guitar with two closely spaced transverse, braces above and below the bridge. That could be another approach worth looking at, though it might be overkill on a body this small. In any case unless the mandolin is totally overbraced, they are going to work. This kind of mandolin will never sound like an F5, but you can put one together in a couple of weekends and have fun playing it.

    cheers

    graham

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  17. #15

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    Here's a new solution I've been working on. This one'll be getting strings in a week, so we'll see........ I resolved the tight spot where the braces meet by progressively carving them into quasi-I-beams near the juncture.
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  19. #16

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    wow. that looks interesting. how does that asymetry work?

  20. #17

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    Taking from where I learned the idea from, the f-hole world, I like to brace in such a way that the bass side of the top taps a lower tone than the treble side. The treble side is therefore given tighter, more concentrated bracing (ping); the bass, looser, and more "spread", (pong). The bridge sits directly over the crux of this arrangement, braces under each foot.

  21. #18

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    That bracing design is too cool! I'm not onboard with tops reacting the way that design is oriented, but if they do, that design should nail it. Great work!

  22. #19
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    I have seen a photo of a flat top for a bouzouki (possibly a Foley?) with a X-brace. Although the arms of the X were of equal lengths, the braces on the bass side were considerably lighter than on the treble side. I think the reasoning behind it was allow the bass side of the top to vibrate more freely, to produce a more even volume across the strings.

    I wonder if the asymmetrical X-brace above is doing a similar thing, but in a slightly different way...

    Patrick

  23. #20

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    I'd refer you to other examples of historical assymetry. The curved bass bar of a lute is placed as such, and tuned in a particular way, to curb the response of the bass, while the trebles "inject"/connect directly to the body, to increase their response.


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    Quote Originally Posted by
    I don't think an X brace is doing much to offset that compression at the tail block and to stop the neck block wanting to rotate
    Graham - I see what you mean. I built my first mandolin (a flat top) with an X, and it sounds great, if I say so myself. On subsequent ones, I've used ladder-type bracing, and none of them has yet compared for tone with the first. I realise that this may well be due to many other factors besides the bracing pattern (I have made every instrument so far to a completely different design), but I would like to go back to the design of my first and try and improve on that (not least, in terms of set-up and playability - which, of course, will be easier, the more stable the body is).

    A question to both Graham and OldTymer: Where does the bridge sit in relation to the braces?

  25. #22

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    I won't comment on the standard x-bracing, but I place the treble foot over the crux of the x, the bass over the smaller spanning brace.

  26. #23

    Default Re: Bracing for flat top mandolins

    Reviving this old thread…is there a particular sound quality or volume benefit from placing a lateral brace directly under the bridge, as opposed to placing braces above, below, or fanned perpendicular to the bridge? Thanks. Dave

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