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Thread: Help: Shaping my first soundboard

  1. #1

    Default Help: Shaping my first soundboard

    Hello. I am currently making my first-ever mandolin based on the F5 model and using Siminoff's book. I am not laboring under any illusions that it will be perfect. So I have made some mistakes, but I have not scrapped the whole project. I want to experience the complete process so that I learn as much as possible.

    I am currently shaping the spruce top. I have used a combination of chisels and planes. The templates I am using are from Siminoff's book.

    You can see in the picture that portions of the top are appropriately shaped. Area "B" is almost perfectly shaped. However, I have not successfully achieved the arched top as you can see in section "A," where there is a substantial gap. Also, in area "C" at the edges, there is a bit of room for the upturned lip on the edge.

    The bad news is that for most of the sections I have achieved appropriate thickness based on Siminoff's templates. So I do not have much material left to spare as I finish up.

    My question is this: What is the best way to finish shaping this top so that all sections are as close as possible to their ideal shape? Can I shave some off of section "B" while retaining its shape, so as to achieve the arch at the top and the upturned lip at the edge?

    Thank you for any suggestions you may have.

    -MarkClick image for larger version. 

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  2. #2
    Registered User sunburst's Avatar
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    Default Re: Help: Shaping my first soundboard

    Quote Originally Posted by putnamm View Post
    ...What is the best way to finish shaping this top so that all sections are as close as possible to their ideal shape?...
    What is the ideal shape? How stiff is the top wood? how dense is the top wood? How does it match up with the back? What is the desired sound?
    Too many questions for a beginner? Probably so... so...
    Just use the template for a general reference, carve a nice, smooth, symmetrical curve and don't worry if the amount of wood doesn't allow an exact match to the template. All will be fine.

    Here's a story for some context.
    When I built my first instrument (a banjo) my plans called for a 15 degree peghead angle. I pondered how to measure and cut a 15 degree angle, asked a math professor for suggestions on how to do it, finally set up an elaborate jig using a miter gauge in a table saw and it turned out my measurement was wrong! I had to re-do the neck, and finally got a 15 degree angle, or at least very close.
    When I started to work at a banjo shop building high end banjos I was curious to see how they established the peghead angle. Turns out they just drew around a neck template and sawed the line on the band saw. Neck blank a little too small? No problem, just reduce the peghead angle a little.
    The point is, without experience we don't know how important certain aspects of building are. Arch shape and height can vary quite a bit, and, with experience we can learn to use arch height and shape to adjust out sound, but for a first instrument none of that matters. All you need is a good arch shape and if it doesn't match someone else's template exactly it doesn't matter. besides, it looks like you still have plenty of material to work with to get very close to your template.

    (You might get some comments on the grain being so far off quarter and the suitability of such grain in a mandolin top. Don't worry about that. If the stiffness and density are anywhere in the acceptable range it will be fine.)

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  4. #3
    harvester of clams Bill McCall's Avatar
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    Default Re: Help: Shaping my first soundboard

    If there's enough wood, you could deepen the recurve. Be easy on yourself, its tough to be born full grown
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  5. #4

    Default Re: Help: Shaping my first soundboard

    Thanks for your input and your story. I understand there are many intricacies in the creating of a musical instrument. In this particular instance, I am really just asking (per my image) if you feel that removing more material from section "B" would be a detriment or not to the end product.

  6. #5
    Registered User fscotte's Avatar
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    Default Re: Help: Shaping my first soundboard

    I reckon leave it as is. I've gravitated to a less Archy top as I go along and find myself using a flatter arch as seen in your pic there. Look ok to me.

    However I don't like the look of your less than vertical grain. That top may be pretty loose.

  7. #6

    Default Re: Help: Shaping my first soundboard

    Thanks, fscotte. Since this was my first attempt, I wasn't overly concerned with the highest possible quality in wood. I have no doubt this will be an imperfect instrument.

  8. #7
    Adrian Minarovic
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    Default Re: Help: Shaping my first soundboard

    Quote Originally Posted by putnamm View Post
    Thanks, fscotte. Since this was my first attempt, I wasn't overly concerned with the highest possible quality in wood. I have no doubt this will be an imperfect instrument.
    I see no problem with the wood. I actually love the bold grain (if the pic doesn't mislead), looks cool. I've used extremely soft Engelmann with much more angled grain and it worked well.
    Regarding the arch I see flat center of top. That would bother me most. Bridge fitting wll be harder and the center might be suspectible to "bridge feet digging" syndrome.
    If it is done to Siminoff thicknesses I bet there is still enough wood to smooth the curve to one long arch. I would use 0.5mm thick flat scraper bent slightly so it removes the bumps (mainly between the A and B areas) and creates the arch. If you don't have scrapers I also have aprox 5"+ square (you can trim the corners to make it more like octagon for safer work on archings) of 1/4" thick cork with really agressive 80 grit Norton sandpaper belt (indestructible stuff by hand sanding) glued permanently (Titebond) to it. Its stifness but flexibility at the same time makes it ideal pad to sand smooth transitions on outside or inside curves (you have to watch the edges not to dig into your recurved areas and work slowly and methodically as the paper is really aggressive).
    The recurve areas look good to me and if they flow nicely into arch I would leave them as they are. Instead of Siminoff thicknesses I would aim at 3.2-3.5 mm at recurve and 4.5 mm at the center (still allows some finish sanding) as start for typical spruce and thin it more if the top feels still stiff in hands or leave it and remove some of the wood after stringing in the white. I would not go below 3.0-4.1 unless the wood is extremely stiff.
    Adrian

  9. #8

    Default Re: Help: Shaping my first soundboard

    Thanks, Adrian and everyone. I built a rudimentary measuring caliper last night using a dial indicator and measured all around the plate. The recurve areas at the edges were exactly where they needed to be, about 0.125". Unfortunately the center was still way too thick, about 0.250". I shaped the whole thing as well as I could. I brought it closer to the true arch top shape, but it's not perfect. Still, I'm apprehensive about pushing any further for fear of screwing up the shape I've achieved. I think now I'm going to try and thin out the center by taking some material out of the back side.

    Appreciate everyone's input.

    Mark

  10. #9
    Registered User sunburst's Avatar
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    Default Re: Help: Shaping my first soundboard

    If you want to see the arch shape better in order to better shape the top, use a single light in a darkened room to side light the arch. That will show high and low areas. Of course, there is nothing you can do to raise low areas, but you can lower the high areas to achieve an even arch.

  11. #10
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    Default Re: Help: Shaping my first soundboard

    Nobody suggested strengthening the braces to compensate for a potentially thin top (probably for a good reason). Is that an option? As a first-time builder, I just carved a "practice" top (oval hole A) out of softwood following Graham McDonald's gradations. It seems very flexible so I'm tempted to beef up the X braces to compensate. Even with the sides on, it has a tap tone of F.

  12. #11
    Registered User sunburst's Avatar
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    Default Re: Help: Shaping my first soundboard

    There is a continuum among builders ranging from thin top with bigger braces to thick top with small braces. It can more-or-less be thought as two "schools" of building.
    The overall stiffness of the completed top is the result of the total structure, and yes, to some extent stiffer braces can compensate for a looser top and vice versa, and in fact two tops using those different approaches can have similar overall stiffness. The distribution of stiffness will likely be different between the two though, so they may well sound different.

    A properly carved mandolin top feels pretty limber, especially to someone without much experience with the feel of carved plates.

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