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Thread: IV A Style Mandolin Build - Back plate question

  1. #1

    Default IV A Style Mandolin Build - Back plate question

    I'm working through my first carved top instrument build (per the thread title, its an IV A-style kit). I've done what I think is a reasonable job on the top, and have worked through getting the neck joint in good working order (it was a disaster as received).

    Now, I'm measuring the back plate and finding that it appears to be significantly too thin for the job. Not just a little, but by almost 1/8" at the center. I'm using the Siminoff plans, and as an example, it calls for .250" at roughly the center of the plate, but without even touching it, I'm at .124".

    I've built some flat top instruments, but this is my first carved top/back instrument, so my intuition tells me that this back is really much too thin to install on this instrument.

    Should I reach out to Ken Wise at International Violin and see if he can provide another back plate?

    This is my first mandolin build, and I don't expect it to be a Loar, but I also don't want to build in mistakes either if possible.

    Thanks for your advice!
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  2. #2
    Registered User amowry's Avatar
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    Default Re: IV A Style Mandolin Build - Back plate question

    It sounds a little thin to me. My quartersawn backs are typically around 0.16" thick in the center and get a little thicker closer to the neck joint. I would ask Ken about it-- he may have experience with that particular wood that indicates that it needs to be that thin.

  3. #3
    Registered User fscotte's Avatar
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    Default Re: IV A Style Mandolin Build - Back plate question

    It may be too thin. Or not.

    The back is the most difficult part to get right and thicknesses will vary from builder to builder, and even build to build. There is also no reasonable way to measure the "correct" thickness you need, with deflection or tap tuning, due to the nature of maple.

    With that said, I've seen back thickness at .115 on some builds (not mine). Others like to stay around .150 or so. My own Gibson A5 is .137 in center.

  4. #4
    Mandolin & Mandola maker
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    Default Re: IV A Style Mandolin Build - Back plate question

    For an oval hole mandolin that is most likely too thin. I say most likely because wood varies so much. If it is a really stiff piece of Maple it might be ok, but my guess is probably not. You can measure the "correct" thickness of the back by using my methods which do actually predict how the mandolin will vibrate when finished (not published yet). The accepted wisdom is everything changes when you assemble the mandolin so the end result is unpredictable. Wrong, and I have the evidence to prove it, but not quite enough to publish yet. It certainly does show why my method does improve consistency from mandolin to mandolin or guitar to guitar. Wait for an article in the GAL, but it might be a long wait. Other things like earning a living take precedence.

    see - http://petercoombe.com/publications/jaamim8.htm
    Peter Coombe - mandolins, mandolas and guitars
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    Registered User Drew Streip's Avatar
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    Default Re: IV A Style Mandolin Build - Back plate question

    Would it be possible to add bracing to a too-thin back in order to strengthen it and add mass? I realize it would be unconventional for a carved instrument, but this seems extreme anyway (almost 50% too thin) so maybe it could be good practice at fitting braces and seeing an adjustment in tone as you add and remove material.

  6. #6
    Teacher, luthier
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    Default Re: IV A Style Mandolin Build - Back plate question

    I don't see why not.
    One or two light braces should be sufficient.

  7. #7
    Mandolin & Mandola maker
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    Default Re: IV A Style Mandolin Build - Back plate question

    Yes you can, I have done it with some success.
    Peter Coombe - mandolins, mandolas and guitars
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  8. #8
    Registered User
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    Default Re: IV A Style Mandolin Build - Back plate question

    I don't understand the hesitancy to contact the supplier/maker as the first course of action if any concerns arise. Call or email. All other speculations should be secondary.

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    Moderator MikeEdgerton's Avatar
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    Default Re: IV A Style Mandolin Build - Back plate question

    Yup, I'd just call Ken.
    "Bargain instruments are no bargains if you can't play them". These are the words of J. Garber.

  11. #10
    Registered User fscotte's Avatar
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    Default Re: IV A Style Mandolin Build - Back plate question

    Back braces are just as good as not having one.

    I've used them when I needed to make the back a bit stiffer.

  12. #11

    Default Re: IV A Style Mandolin Build - Back plate question

    Thanks much for all the input everyone.

    No hesitance to reach out to IV, they just were not open on Sunday when I was working in the shop, and this group is a great resource to ask (after reading every thread I could via the search function).

    I did reach out to Ken. He suggested that the back actually might need to be a little thinner than it was as received, but likely was good when it was finish sanded.

    We'll see how this one turns out. I'll make note of what the back was like and try to learn from it.
    Chinn BluesBird Emando #1
    Aria M-300BG 2 Point
    Michael Kelly Legacy O
    Kay Model 68
    Stoneman Travel Mando

  13. #12
    Registered User fscotte's Avatar
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    Default Re: IV A Style Mandolin Build - Back plate question

    Just so you know, it appears that many Loars were sanded down after assembly, suggesting that they were "tuned" by making the backs stiffer than they need to be at the start, and slowly sanding away stiffness to balance out the tone.

    I think you're smart to just go with the .115 centered back. It will likely not give you any problems structurally.

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