First Falcate underway! Plate Thickness question?

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chrisbaer
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First Falcate underway! Plate Thickness question?

Post by chrisbaer » Thu Aug 16, 2018 8:38 am

So I'm finally getting around to making a Falcate braced steel string guitar! Very exciting!

I have a couple of questions about plate thickness.

For the Top plate, Trevor lists an f value of 75 to plug into the thickness calculation, but doesn't specify the bracing. For my bear claw sitka top, I get 3mm with an f value of 75, 2.8mm for 70, and 2.6 for 65. Should I use a lower value for falcate bracing?

For the live back plate, I have a nice piece of Madagascar Rosewood - it seems quite dense and stiff. I got some odd values when I tapped it. I tried a few times and got pretty consistent results. It is not a perfect rectangle, but reasonably close.

Flong = 81
Fcross = 80
Fdiag = 67
Mass = 359
Thickness = 4.2

With an f value of 55, I get 2.58mm target thickness. That seems thin to me, but I haven't made one of these kinds of guitars yet.

Do these seem like reasonable numbers?

Thanks!

Chris

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Trevor Gore
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Re: First Falcate underway! Plate Thickness question?

Post by Trevor Gore » Thu Aug 16, 2018 11:18 am

chrisbaer wrote:
Thu Aug 16, 2018 8:38 am
For the Top plate, Trevor lists an f value of 75 to plug into the thickness calculation, but doesn't specify the bracing. For my bear claw sitka top, I get 3mm with an f value of 75, 2.8mm for 70, and 2.6 for 65. Should I use a lower value for falcate bracing?
I use 75 with falcate bracing as per the plan in the back of the Build book. Bearclaw can be less stiff than straight grained timber, thus requiring you to leave it thicker to get the same target vibrational frequencies.
chrisbaer wrote:
Thu Aug 16, 2018 8:38 am
With an f value of 55, I get 2.58mm target thickness. That seems thin to me, but I haven't made one of these kinds of guitars yet.

Do these seem like reasonable numbers?
Yes. That's typical of what I would expect for a live back.

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lamanoditrento
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Re: First Falcate underway! Plate Thickness question?

Post by lamanoditrento » Thu Aug 16, 2018 3:34 pm

Congrats Chris on passing the ANLF target thickness rite of passage :D

chrisbaer
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Re: First Falcate underway! Plate Thickness question?

Post by chrisbaer » Fri Aug 17, 2018 3:07 am

Thanks, Trent! I'll feel more of a sense of accomplishment once the top is fully braced! (Fingers crossed)

chrisbaer
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Re: First Falcate underway! Plate Thickness question?

Post by chrisbaer » Fri Aug 17, 2018 3:07 am

Thanks, Trevor! Full steam ahead, then!

chrisbaer
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Re: First Falcate underway! Plate Thickness question?

Post by chrisbaer » Tue Sep 04, 2018 1:49 am

IMG_0412 (1).jpg
Well, it isn't pretty (I obviously have to work on my epoxy spreading skills!), but my first falcate top is glued up! Thanks for the help thus far!

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