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Thread: Top wood for bowl backs - source

  1. #26

    Default Re: Top wood for bowl backs - source

    Although Helmholtz and Lord Rayleigh had laid down the most of the relevant acoustic physics before my mandolin was made, there remains quite a bit of the non-intuitive going on, so I wouldn’t think my guesses about how the thing radiates would be more than simplifications.
    So, in addition to the structure in question, there are also side ports and sometimes twin tiny top ports of unknown purpose. I suppose one could put the stems of fresh flowers into these apertures, or assume they are brilliant anticipations of electronic aids of the future.
    If we wanted to second-guess some of these things, we might also take a look at the now definitive, but originally weird layout of Gibson’s F, and imagine that something other than decoration was the motivation. We could also find something better to do..

  2. #27
    Full Grown and Cussin' brunello97's Avatar
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    Default Re: Top wood for bowl backs - source

    Richard

    Okay.....sorry for the long delay, but I've finally turned up the supplier for bowlback tops / tonewoods that I spoke about in an earlier message.

    By coincidence, after searching through email archives, I found his business card in a jar I keep old picks, etc.

    Here goes:

    Simeon Chambers "Englemann Spruce Specialist"
    Rocky Mountain Tonewood
    303-507 5225
    chamberssim@qwest.net

    53 Sylvestor Place
    Highlands Ranch, CO 80129

    This contact info is more than a few years old now, so no guarantees....

    The wood I got from him...and I still have some left...was very good.

    Hopefully you can make contact.

    Mick
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  3. #28

    Default Re: Top wood for bowl backs - source

    Just for reference, I bought some spruce intended for concert or tenor ukulele that is approximately a usable thickness for a bowl back and long enough. Not expensive.
    Coming in this week (US). A sharp, linear heat bend is needed for the usual cant, so I think that’s either one of my strip heaters clamped to a straightedge, or same clamped to a clothes iron. Shouldn’t be difficult. Will report back if anything unusual gets involved in this rescue as I do it. Because of the original massive pick guard/soundhole surround, I doubt that fine-tuning the top thickness is relevant.
    Also sketched out what I think is a bowl clamping setup as the neck block is separated. Could be messy.

  4. #29
    Registered User j. condino's Avatar
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    Default Re: Top wood for bowl backs - source

    Quote Originally Posted by Richard500 View Post
    "........... I doubt that fine-tuning the top thickness is relevant..........."


    Said no one ever in the history of making musical instruments that knew what they were doing or cared about the end results!!!!!!!!!!!

    Do you have a copy of Alfred Woll's book on making bowlback mandolins? I highly recommend it for this project.
    www.condino.com

    Crafted by hand in a workshop powered by the sun.

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  6. #30
    Registered User sebastiaan56's Avatar
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    Default Re: Top wood for bowl backs - source

    Quote Originally Posted by Richard500 View Post
    Just for reference, I bought some spruce intended for concert or tenor ukulele that is approximately a usable thickness for a bowl back and long enough. Not expensive.
    Coming in this week (US). A sharp, linear heat bend is needed for the usual cant, so I think that’s either one of my strip heaters clamped to a straightedge, or same clamped to a clothes iron. Shouldn’t be difficult. Will report back if anything unusual gets involved in this rescue as I do it. Because of the original massive pick guard/soundhole surround, I doubt that fine-tuning the top thickness is relevant.
    Also sketched out what I think is a bowl clamping setup as the neck block is separated. Could be messy.
    Graham MacDonald describes the process of creating a cant in his Mandolin Project book. Score and clean out the back, profile with a file before bending. You will also need to take into account the curvature of the soundboard. I have seen some very high curves.

    2.5-3mm is the standard soundboard thickness range at the moment. The bracing is very important for the integrity of canted boards. The inlays on the soundboard dont directly affect the sound. It’s the area below the cant that does the bulk of the sound production. Cant angle and curvature should be big areas of interest for you.

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  8. #31

    Default Re: Top wood for bowl backs - source

    Got the top off. Speculation that it wasn’t original seems accurate as the bracing is unlike that of a close year model, and is crude. Since two likely original spruce bits remain flanking and under the fretboard end, at least the thickness there can be measured. Photos of others indicate the top lateral curvature, and the cant has to fit the bowl. Just for curiosity, I think a magnetic thickness gauge is in order to see if any of the Italian ones I have are uniform or have gradation. Another gizmo to make.
    I’ve read the discussion here about how to make the center seam join on a curved and canted top, which involves some geometry, and currently guess that a template or a sacrificial top is the easiest way to do it.
    Sebastiaan56 is correct in that the area aft of the bridge is accepted as the most compliant and therefore important membrane, and also the least supported. Since the string hold-down in that area influences the stiffness, it’s not just an insignificant piece and should be located close to the original position. Something else to think about.
    And the ‘tulip’ binding/edging brings up the question of what wood this is. Not what it’s called in the US. Looks more like a very fine grained fruitwood.
    Meanwhile, a Portuguese guitarra rescue is back together, Preston tuner parts made, and strung up as a mandola. Nice sound, but the C isn’t pleasant at the usual gauge, so may get changed. May also sport some nylons for a test. The temporary bridge for fitting is in ipe, which was handy and dense, and may continue. Original may have been all bone or bone saddle. Guitarras are radiused so the bridge should follow - maybe.

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  10. #32
    Registered User Tavy's Avatar
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    Default Re: Top wood for bowl backs - source

    Re binding google "brazillian tulipwood": it's a true rosewood, but grows as a bush not a tree so is only available in small pieces, and since it's a shrub rather than a tree it's not endangered either so far as I know. Most supplies are of blanks for pen turners and such like, they key is to cut it in the right direction to get the pattern to show. Other than that, it's an exact match for DeMeglio binding once finished with shellac.

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  12. #33
    Likes quaint instruments poul hansen's Avatar
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    Default Re: Top wood for bowl backs - source

    Quote Originally Posted by Jim Garber View Post
    Would you really need to use steam to de-warp the top and close up cracks? I have had some of my luthiers just use cool humdification by putting the instrument in a plastic bag with some water for a week or two.
    You are probably right. I guess I was a bit impatient.

    On the other hand: When I first tried to close gaps I put a guitar in a plasticbag with the opening over a humifier and kept it manually at 80% but it had no regulation so the day I forgot it it went to 100% and top, bottom and sides just opened at the bottom, where some condensation had gathered, so now I only humify while watching.
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  13. #34
    Full Grown and Cussin' brunello97's Avatar
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    Default Re: Top wood for bowl backs - source

    Quote Originally Posted by sebastiaan56 View Post
    You will also need to take into account the curvature of the soundboard. I have seen some very high curves.
    That's what I know.

    I had an old "Lanfranco e Figli" MOR bowl that had a cross top curvature that would make an F-5 proud.

    It was a bit shocking, really. The bridge had the profile of a potato chip.

    Un bol ordinaire for sure, but it was unique in that respect.

    Mick
    Ever tried, ever failed? No matter. Try again, fail again. Fail better.--Samuel Beckett
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