12 string back braced up

[kiwigeo]

The end results of todays efforts in the workshop. Got the 12 string back braced up and ready to go on the body. Bracing is Sitka Spruce as is the centre seam strip. The back is Indian Rosewood from LMI (opportunity grade).

[TimS]

Hi Martin,

Does your x brace sit on the centre seam or through it? Does the numbering relate to plate thickness?

regards

Tim

[kiwigeo]

Hi Tim,

X brace sits on the back. Centre seam strip has been cut to fit the brace.
The numbers are the calipered thickness of the ends of the braces where theyll tuck into the linings.

Cheers Martin

[TimS]

Hi Martin,

Thanks for the information.

regards

Tim

[matthew]

Again, cos I don't understand guitars yet ... what happens if you *don't* tuck the ends of the braces into the linings, but just graduate them down to zero at the tips?

[TimS]

Here is my ten cents worth!

If the back bracing is not tied into the sides/linings then there will be more movement. Too much movement might mean structural failure. As I see it the back plate I believe acts like a reflector of sound so if there is too much movement perhaps there will be a loss of sound or a change in tone. Having said that there are double backs which I think don't have any bracing (not sure). If you were referring to the top plate where there is more direct tension from the strings, a lack of bracing tied into the side may over time cause the top to implode around the waist/soundhole area.

Any way that is my ten cents worth for the day.

regards

Tim

[Dennis Leahy]

Tim, the 2 schools of thought (that I have read) on that are:

Stiff, highly reflective back = projection

Looser, more vibrational back = more radiated sound near the guitar especially to the player

Now you'll have to build one of each and see what you like better!

Of course, I guess there are a million shades of gray between those extremes as well.

Dennis

[Bob Connor]

On our last few guitars we have graduated the back braces down to nothing and let the sides squash the remaining sliver of spruce.

I feel that it does make for a very personal sounding and feeling guitar.

You can feel the back vibrating aginst you chest when you play it and it makes for a little extra coupling with the top.

[kiwigeo]

Again, cos I don't understand guitars yet ... what happens if you *don't* tuck the ends of the braces into the linings, but just graduate them down to zero at the tips?

I do it mainly for structural reasons. Housing the brace end into the lining adds strength to the back and IMO helps keep arch in the back also.

The argument regarding whether or not a back should be free to vibrate is a many sided debate. Allan Carruth has some interesting and well thought out ideas on this subject. His work on the physics of the guitar are well worth a read.

[Serge]

Looking good Martin, keep it up bro!

[joel]

What is opportunity grade? Is it the same as the 2nd grade stuff you see at lmii or allied lutherie? Is there an Aussie place to get some?

[kiwigeo]

Occasionally LMI has opportunity grade wood available. Its low grade stuff that doesnt make 2nd grade due to knots, pinholes or other blemishes but its still usable. usually the template can be placed to avoid most of the major blemishes and if that doesnt work a bit of work with CA glue can often do the trick.

I havent seen any opp grade IRW on LMI for a while. I got mine about 3 years ago.

Tim Spittle is waiting on a consignment of IRW so PM him if youre interested. Occassionally Dave Freeman at Timeless Instruments has opp grade wood.