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| X- braced back question http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=26663 |
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| Author: | sailorman [ Tue Mar 23, 2010 8:23 am ] |
| Post subject: | X- braced back question |
I am building a OLF small jumbo(my first), and I've chosen the optional X bracing for the back. I've seen some sort of graft that captures the top of the X and I'm wondering if there are any photos available. Thanks, Rob |
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| Author: | JohnAbercrombie [ Tue Mar 23, 2010 11:12 am ] |
| Post subject: | Re: X- braced back question |
Rob- I don't know if you are talking about the 'cap' that's commonly used on X-braces for the soundboard, as well as on back 'X' braces?? (I've seen some 'bulky' '+' type caps on X-braces, which are much bigger than necessary....) There's a good discussion of X-brace caps about 2/3 down on this page by Ervin Somoygi: http://www.esomogyi.com/principles.html The cap doesn't have to be very thick to do the job. Cheers John |
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| Author: | Wayne Clark [ Tue Mar 23, 2010 2:58 pm ] |
| Post subject: | Re: X- braced back question |
Here is a pic of my latest. The cap on the x-brace is a good idea, and adds a little more strength to the joint. I don't think it needs to be very big. I usually use a piece of the scrap wood left over when I cut the back to its rough shape. Attachment: feb 2010 039_2.jpg
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| Author: | sailorman [ Tue Mar 23, 2010 3:18 pm ] |
| Post subject: | Re: X- braced back question |
Thanks, My plans show two additional braces running paralell to the ladder braces and mitered into the X. I see in your photo that you don't have these. Can I get away without them? My guitar has an english sycamore back and sides about 2.8mm. |
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| Author: | Link Van Cleave [ Tue Mar 23, 2010 4:42 pm ] |
| Post subject: | Re: X- braced back question |
Quote: The cap on the x-brace is a good idea, and adds a little more strength to the joint. Wayne, I think you win the understatement award.  It adds a lot more strength, especially if the joint was poorly made in the first place. Even if well made the extra height from the cap makes a huge difference. The now platitudinous "cube rule" applies. Link |
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| Author: | Pat Foster [ Tue Mar 23, 2010 5:06 pm ] |
| Post subject: | Re: X- braced back question |
While the cap does add strength from extra height, I think it does a lot more for the joint by working in tension to preserve the integrity of the joint, which is why it's so effective even if it's very thin. Just my .02. Pat |
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| Author: | Mike Collins [ Tue Mar 23, 2010 5:09 pm ] |
| Post subject: | Re: X- braced back question |
If the lap joint is made properly -you do NOT need a cap. Mike |
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| Author: | Fred Tellier [ Tue Mar 23, 2010 5:11 pm ] |
| Post subject: | Re: X- braced back question |
I am wondering if any benefit in strength or sound is achieved by using a back X brace. Please enlighten me Fred |
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| Author: | JohnAbercrombie [ Tue Mar 23, 2010 6:51 pm ] |
| Post subject: | Re: X- braced back question |
Mike Collins wrote: If the lap joint is made properly -you do NOT need a cap. Mike Mike- By 'properly', you mean not half-lapped - ie very shallow notch in the brace crossing 'under'? Do you make your X-braces both the same height, or one taller? Cheers John |
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| Author: | JohnAbercrombie [ Tue Mar 23, 2010 6:59 pm ] |
| Post subject: | Re: X- braced back question |
Fred Tellier wrote: I am wondering if any benefit in strength or sound is achieved by using a back X brace. Please enlighten me Fred Fred- Enlightenment is not my department at all!  Check with some of the more mystical folks for that...Sound-wise- well that's an ongoing discussion - how much does the back contribute? Strength- Well, what shape is the arch on the back? If it is cylindrical, it makes sense to ladder-brace it (like a Quonset hut...) If it's hemispherical, the X seems to make more sense, to me. It certainly looks cool to me- I've used it a few times - both single and double-X. Probably conservative folks who want to see the inside look like a Martin wouldn't like the X showing on the back. Keeping the back from flattening out is a good thing, no? It makes it harder for the neck block to rotate. Whether the X is much better at this is the question. Cheers John |
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| Author: | Wayne Clark [ Tue Mar 23, 2010 11:24 pm ] |
| Post subject: | Re: X- braced back question |
sailorman wrote: Thanks, My plans show two additional braces running paralell to the ladder braces and mitered into the X. I see in your photo that you don't have these. Can I get away without them? My guitar has an english sycamore back and sides about 2.8mm. My plans don't have the two additional braces. Maybe there is a newer version of the plans. The back on this one seems stiff enough. |
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