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Im currently working on bracing for a 12 string. Top is Lutz spruce and around the bridge area its worked to 0.130". rest of top is about 0.125" thinning to 0.110" around perimeter of top.

Ive scalloped the long arms of the cross brace so theres peak one third of the way down the brace. The peak is about where the saddle will be.

Id like a critique of the scalloping on the cross brace. Am I in danger of having the top in front of the bridge hollow out or will I be ok?

Any thoughts welcome.

Heres the pic

Better pic showing upper tone bar in place.

Okay, Since any thoughts are welcome.

Did the chisel get away from ya there?

I think it's a wee bit pared away there near the x and bridge plate.

I'd chisel them off and try again.

But it does really look nice, great job in the surgery.

Good luck, and yeah, It looks like it might implode or explode to me. I've been wrong before, so if you have lots of time to build prototypes, keep up the good work.

Now, I hope those thoughts were welcome.   

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http://www.dickeyguitars.com

Of course, if this works and you prove it's better, we'll all be building 'em this way the next week.....

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http://www.dickeyguitars.com

What, did you say 12 string? Geeze, this thing is gonna blow under the pressure of two sets of strings.

Why not peek inside a 12 string and see what kind of bracing they need. Is that cheating? I just sold my Alvarez 12 so I'm no help.

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http://www.dickeyguitars.com

What's the theory?
Looks like a recipe for collapse and disaster to me...even on a six string.   

Since you asked....personally I thing iyts too scalloped between the X and the bridge. I would space out the scalloped area and move the peak about one inch outwards.....

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Peter M.
Cornerstone Guitars
http://www.cornerstoneukes.com

Thanks chaps,

Youve confirmed what Im already thinking. Off comes the cross brace then.

Rick, the theory? To try and do something really stupid and see if people in here don't notice

Cheers Martin

Well, God bless you if you have the time on your hands to do that, but if you're trying to get "from here to there" with guitar making, then you might consider going with the tried and true for a few before building the guitar equivalent of a balsa balcony railing in a movie set western bar for cowboys to crash through on camera!

Don't forget that scalloping bracing is a deliberate and usually incredibly successful attempt at weakening the braces in order to control the nodal response of the top at certain frequencies. This is one of those structure vs. tone issues.

Yikes Martin ! If you are to scallop at all , start well past the bridge . I've chosen to use tapered bracing for my 12 with the parabolic type shape. Here's a pic of mine

Hope this helps

Cheers Craig

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CRAIG LAWRENCE of AUSTRALIA
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Martin...I'm searching from memory here as to the key points others have stated when designing bracing for a 12 string. Here are some items I remember:

...5/16" X-bracing scallopped similarly to that of a 6 string...voice accordingly but err on the side of heavier bracing. Some have stated that their 12 string bracing departs little from 6 string.
...1/4" tone bars...some have added a 3rd tone bar (like Craig) but I've seen a lot with only 2
...Slightly thicker top...yours sounds like a good start depending on thickness.

Hopefully this will generate some comments from others who know more.

BTW...I commend you for speaking up on this before gluing that top to the sides...you must have had a sense that it might be a potential bomb.

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JJ
Napa, CA
http://www.DonohueGuitars.com

Craig, thanks for the pic. Most helpful.

I say leave it this way but ramp it so you cap the lengths with carbon fiber rod up to the crossing of the x just to see what you get. Call it a feature.

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"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

Sorry, for some reason it made me think of Taylor's route around the lower bout.

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"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

Kiwigeo ,you need to understand where tops flex and its not where your braces are!
Kiwicraige, your top is over braced!
Lance

Appreciate your opinion Lance .It's an Englemann top and fairly light . I have the box closed now and am getting a G# from the top ,without bridge . It seems quite responsive and ( was ) fairly happy with it.
The lowest tonebar is only 5 m.m. and the rest have had been carved away till they are quite thin .As this is my first 12 string , I had advice from a very experienced builder here in Australia ,who has built many successful 12's, He emphasized a large bridge patch and not to scallop.

Where do you think I should lighten up ?

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CRAIG LAWRENCE of AUSTRALIA
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Surgery is nearly complete...Ive gone for a tapered cross brace and three tone bars as on Craig's instrument.

On ya Martin .You'll sleep better at night

Another thing I was advised was to locate the first tonebar up close to the bridge patch , and have it angled so that the end of it almost intersects the crossbrace at it's end.
I note Taylor and others do this also.

Cheers, Craig

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CRAIG LAWRENCE of AUSTRALIA
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Dang that edit button !

Lowden now uses 3 tonebars on his six string guitars !!!

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CRAIG LAWRENCE of AUSTRALIA
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[QUOTE=KiwiCraig]
On ya Martin .You'll sleep better at night


[/QUOTE]

Thanks to Rick Ive already had more than one nightmare featuring guitar playing cowboys crashing through balsa wood ballastrades!

     

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CRAIG LAWRENCE of AUSTRALIA
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After some major surgery on the cross brace and a rethink of the bracing on the lower bout here's what I've finished up with.