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Thread: Top and back graduations

  1. #26
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    Default Re: Top and back graduations

    I am using the Griffith Loar plans. I have shifted the height of contour on the top to under the bridge. Tone bars are smaller than what is on the plans and are checked by my mentor, James, before going on. He has been a saint helping me with trying to voice them all. #5 is in the white. I will measure it and sent come pics of the graduations. I use a Magic Probe to measure after closing up. I have discovered that it is dead on in the convex areas but .003-.005 of in the concave areas. I believe that the diameter of the tip is large enough to effect the accuracy of the concave areas. Adrian, I got you to send me a link to your voicing post. Great stuff. Do you have drawings for the Griffith Loar?
    Thanks guys, Graham

  2. #27

    Default Re: Top and back graduations

    Is it possible your spruce is exceptionally stiff and you still have too much wood?
    Has your mentor had your plates in hand to feel, scratch and flex before you glued them up?
    Is it possible you have not played them in, as they say about red spruce?

  3. #28
    Adrian Minarovic
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    Default Re: Top and back graduations

    Quote Originally Posted by graham darden View Post
    I am using the Griffith Loar plans. I have shifted the height of contour on the top to under the bridge. Tone bars are smaller than what is on the plans and are checked by my mentor, James, before going on. He has been a saint helping me with trying to voice them all. #5 is in the white. I will measure it and sent come pics of the graduations. I use a Magic Probe to measure after closing up. I have discovered that it is dead on in the convex areas but .003-.005 of in the concave areas. I believe that the diameter of the tip is large enough to effect the accuracy of the concave areas. Adrian, I got you to send me a link to your voicing post. Great stuff. Do you have drawings for the Griffith Loar?
    Thanks guys, Graham
    I haven't seen the Griffith Loar plans in person so I cannot comment on those. From detailed photos of that one I see that the top either has undergone quite a deformation or the arch was carver a bit off towards the tailpiece - or most likely both of these being one-off carved on oval A form that actually has the highest spot of arch closer to tailpiece (position of bridge on ovals is closer to tailpiece).
    This results in what violin makers would refer to as "camel" arch. In the case of Griffith there is just one large hump between tailpiece and bridge and flat area under bridge. Tonally mandolins (F-5's) with thinner tops and arch like this tend to have sweet response especially in lower registers and airy higher notes but not much of the "knock on wood" that makes them loud. These are my main reasons why I would not try to copy that one without "correcting" some aspects that I personally don't like.

    My voicing thread is here: https://www.mandolincafe.com/forum/t...Outside-tuning
    Adrian

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  5. #29
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    Default Re: Top and back graduations

    Some years ago when Lynn Dudenbostle had the Griffith Loar in for some repair work, he described the arching to me. As far as I can tell from that, it would be safe to assume that Gibson used the same templates they used for their oval hole mandolins to make the Griffith Loar. I looked at my Gibson oval hole and the arching fitted Lynn's description exactly, except of course in the sound hole area.
    Peter Coombe - mandolins, mandolas and guitars
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  7. #30
    Adrian Minarovic
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    Default Re: Top and back graduations

    Quote Originally Posted by peter.coombe View Post
    Some years ago when Lynn Dudenbostle had the Griffith Loar in for some repair work, he described the arching to me. As far as I can tell from that, it would be safe to assume that Gibson used the same templates they used for their oval hole mandolins to make the Griffith Loar. I looked at my Gibson oval hole and the arching fitted Lynn's description exactly, except of course in the sound hole area.
    I agree that it most likely started similar to ovals of the era but after seeing some recent photographs I believe there is some sinking in the bridge area and also slightly towards fingerboard and the bulge behind bridge is a bit fuller than on ovals.
    Adrian

  8. #31

    Default Re: Top and back graduations

    No offense intended to anyone here or in other threads, but I secretly get endless entertainment from all the thread comments about the Griffith Loar by people who have never played it.

    I have...and 'hack'd it...and poked around it extensively. I distinctly remember four things:

    1)It didn't follow the usual rules, but it also didn't not follow them.

    2)The fretwork was mediocre; if I tried to pass off anything like that, I'd get yelled at today.

    3)It kicked a$$ as its own unique instrument, but did nothing to make me want to copy or own it. 'Better to integrate some of its ideas into my own work.

    4) MOST important- the voice was as good as any F model I have played or heard, but it didn't have anything to do with Loar unicorns and fairy dust.....

    Imagine a world where instruments of such historic significance like this were accessible to players and builders rather than being locked away in a private vault. I've been unsuccessfully trying for years to get access to it again to make a very accurate plan for everyone else to be able to understand all the subtle details. If you take HoGo's exceptional F5 blueprint and combine it with my snakehead A blueprint from the Guild of American Luthiers, 95% of what you need will be right there. The rest is in your hands and your heart.

    j.
    Last edited by grandcanyonminstrel; Nov-18-2019 at 3:14am.
    Spruce dork

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  10. #32
    Registered User Tom Haywood's Avatar
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    Default Re: Top and back graduations

    Views about Loar thickness graduations ultimately come down to beliefs. My experience has led to a belief that I've not read anywhere, so here it is in a nutshell. Mr. Loar had some kind of a degree in acoustical engineering, which means he studied Helmholtz, the design of wind instruments, and the physics of strings. The oscilloscope was invented and being used around 1915, so he had a new and precise way to specify and measure a variety of frequencies. His primary goal was to manage a repeatable, consistent factory process. Helmholtz was very specific about the sound chamber frequency in wind instruments, and about the thickness of the walls of the chamber in producing the tonal qualities. Getting the walls of the sound box to a certain and consistent thickness would have been important to Loar. Unlike metal, the large differences in species and individual pieces of wood required something more than just thickness measurements to achieve the tonal properties. The thickness measurements get you in the ballpark for the woods he specified (and many more); tapping, listening and feeling the flexibility, along with tone bar thickness adjustments, give you the "something more". Interestingly, these rough measurements, along with the cubic size of the chamber and the size of the openings, come together to give you a sound box having very close to the ideal Helmholtz frequency specified by Loar, which projects the instrument. I think that is the main goal of his thickness measurements. Structural support plays into it to a much lesser degree due to the arching.

    Of course, it is not necessary to repeat Loar's specifications and processes to make a good sounding mandolin.
    Tom
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  11. #33
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    Default Re: Top and back graduations

    I saw the Tucker in the classifieds and shared it with Jacob Hagerty who is beginning to build some nice mandolins. It is an extreme example of one way to do the recurve. But watching and listening to the video you sure can't say it's wrong.
    I've always referred to this picture from the Archive as an example of how a Loar is done. Not as extreme as the Tucker but still a pretty well scooped recurve. What I was referring to about getting the shape right or else the graduations are meaninless.
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  13. #34
    Adrian Minarovic
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    Default Re: Top and back graduations

    Quote Originally Posted by Jim Hilburn View Post
    I saw the Tucker in the classifieds and shared it with Jacob Hagerty who is beginning to build some nice mandolins. It is an extreme example of one way to do the recurve. But watching and listening to the video you sure can't say it's wrong.
    I've always referred to this picture from the Archive as an example of how a Loar is done. Not as extreme as the Tucker but still a pretty well scooped recurve. What I was referring to about getting the shape right or else the graduations are meaninless.
    I might add that the reflections in that photograph may be a bit misleading to think the recurve is quite far away from edge near tailpiece. You need to study the composition and lighting of the scene to understand how the arch looks. The mandolin was leaning against couch leaning away from photographer and light apparently enters through door on opposite wall of the room right behind the photographer. With this in mind we can assume that the light comes at angle from tailpiece side of mandolin and lightest reflection is not on the bottom of recurve near tailpiece but on the side rising into arch. The bottom in this case is right at the transition between the light and dark areas. On the left and right side of instrument this angle (in roughly same vertical plane as direction of recurve) doesn't play role and bottom is reflecting most light. (you can also notice that the main reflection of the door is not below bridge in the center of plate, but rather towards tailpiece where the top slopes down, same is visible on the scroll - the horizontal part reflects light on the downhill slope and the vertical right on the ridge)
    Adrian

  14. #35
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    Default Re: Top and back graduations

    I don't know, but I'm seeing the bottom of the recurve under the tailpiece as being at least half way up in the center of the TP. But the other giveaway is how the recurve narrows along the sides to nearly nonexistent at the scroll and point.

  15. #36
    Adrian Minarovic
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    Default Re: Top and back graduations

    Here is where I see the bottom of the recurve (I marked it on th mandolin with red line):
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    Adrian

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  17. #37
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    Default Re: Top and back graduations

    Interesting that the recurve is not a constant distance from the side. Very nice work BTW
    Graham

  18. #38
    Adrian Minarovic
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    Default Re: Top and back graduations

    The recurve (meaning the channel deeper than edge) is roughly parallel to edge up to the f hole or widest part of top and from there the recurve gradually vanishes both in depth and width. There is no recurve at the scroll, just smooth flat transition towards edge near neck and inside of scroll. Even the scroll ridge doesn't reach past the "A-style body outline".
    Adrian

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