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Carbon fiber bars & top thickness
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Author:  Laurent Brondel [ Fri Feb 24, 2006 4:08 am ]
Post subject: 
In thinking of my next builds and trying to solve problems with my 1st
build I came up with this:
I used 2 x carbon fiber reinforcements for the neck of my first build, in
addtion to the truss-rod, with the idea of minimizing the geometry
changes when using different tunings. Mahogany dovetail neck, Martin
style. The neck is obviously very stiff but I still get changes in geometry
when retuning because of the changing tension on the sitka top. I built
very light (the plates were very stiff), around .095 thickness and feathered
around the edges, ultra-scalopped bracing.
Now I have an OM-21 for some time at home, a very good sounding
guitar by the way, much lighter and much more responsive than the
OM-28Vs I've played before. Obviously the OM-21 neck does not have
carbon fiber bars, and the top/bracing system is a loss less flexible
(thicker) than my build. No issue when retuning with the OM-21.
Although I really like the sound of the OM-21, my 000 build has more of
everything: bass, treble, volume, dynamic range, definition etc.
Any suggestion? It's a delicate balance, I know some builders tend to
build heavier than others and still get excellent results, what would be
your suggestions for keeping a fairly stiff system and prevent the action
changes occuring when using different tunings, and still retain a very
"open" sound?
Author:  Dave White [ Fri Feb 24, 2006 4:49 am ]
Post subject: 
Laurent,

Can you be a little more specific about the tuning changes and what happens to the playing action (e.g describe one tuning change to another and the action changes - all strings, some strings etc).

What arch/dome was in your top? You could leave the centre of your tops a little thicker and feather out from there and brace accordingly to keep the top responsive.

If you play in a lot of tunings it can be a little tricky, especially as they have different "balances" - the DADGAD tunings low at the extremes, but the C tunings having the second sting high at C and the 5th and 6th down to C and G, and finding the right string gauge combination can be challenging. Colin S advocates a guitar for each tuning with suitable string sets

I move hugely between tunings and also have the twin carbon fibre re-enforced necks and don't have issues of action changes. It could be I not as sensitive to them as you and they are occuring, but my tops in the middle tend to be nearer 0.12" and much thinner at the edges, and I also have pretty big arches in the top especially side to side.
Author:  Laurent Brondel [ Fri Feb 24, 2006 5:55 am ]
Post subject: 
Can you be a little more specific about the tuning changes and what
happens to the playing action (e.g describe one tuning change to another
and the action changes - all strings, some strings etc).

Mainly the tuning changes: going from standard to ornkey for example I
have to retune ALL the strings, lowering the low E, A, B and high E strings
for example will raise the pitch of the D and G. It's subtle but enough to
be bothersome. Also action changes slightly, lower tunings bringing it a
little too low and vice-versa for higher tunings. I go from standard to
ornkey to DADGAD and their variations, about 5 or 6 tunings. The most I
detune is the low E to C, and the G to E.

What arch/dome was in your top? You could leave the centre of your
tops a little thicker and feather out from there and brace accordingly to
keep the top responsive.

Arch is 25' radius I believe, I suppose I thinned my top a little too much,
but that's the kind of sound I'm after.

Colin S advocates a guitar for each tuning with suitable string sets

Yes, me too… Just not too practical in most instances to shlep 4 or 5
guitars! Besides the cost of course… BTW I found a set that works well
(and feel right) for all tunings I use: 12 16 23 30 42 56 on a 26.5" scale.

It could be I not as sensitive to them as you and they are occuring, but
my tops in the middle tend to be nearer 0.12" and much thinner at the
edges, and I also have pretty big arches in the top especially side to side.


Thanks Dave, that's a measurement. I assume you go even a little thicker
for a red cedar top? Yeah I tend to play with a fairly low action
(.070 to .090 at 12th fret). What's the radius you use for top and back? By
looking at Sobell's guitar for example, I assume he use a fairly
pronounced arch.
Author:  Dave White [ Fri Feb 24, 2006 8:36 am ]
Post subject: 
Laurent,

I think you need to make tuning changes part of the performance like Martin Simpson does If I had a pound for every person I've heard say at his Workshops that they would just like to learn to play what he plays as he retunes, I'd earn a better living than as a guitar builder

Th jigs I use to shape the bottom of my braces with are around 14' radius for the backs and 16' radius for the tops, but they don't come out spherical and the lateral arch is not as severe as those on Stefan's guitars. This is goverened largely by where the braces go. On my tops there is more of a lateral arch, but even here it is a bit flatter in the middle - governed by the bridge plate and behind the bridgeplate brace. From the soundhole back there is more of a front to back arch:





Another thing that I think helps the neck body stability is the carbon fibre buttress braces that go from the sides to the neckblock.
Author:  Colin S [ Fri Feb 24, 2006 9:45 pm ]
Post subject: 
The four main altered tunings I use are:

DADGad, obviously
CGDGad, Low C
DGDGbd, Open G
DADF#ad, Open D

I use the same dedicated guitar for all four. I tend to play very light strings, and build accordingly. The set I use on this guitar compared to my normal strings is:
12(10),16(14),23,30,42(39),54(47), Scale length 645mm (25.4"). Before I used Low C I had a 52 on the 6th. All my necks have carbon rods. So I only have to have to take three guitars and a lute out with me. Mahogany/Euro OM for altered tunings, mahogany/euro OM for standard tunings, ensemble and my singing, BRW/euro OOO for my wife's singing and pipes. Oh and a mahogany/adi OO for blues. So that's four guitars and a lute! Oh well! (no I'd need a Strat for that!)

Colin
Colin S38773.3951967593
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