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1st Top - Bracing Critique
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Author:  justink [ Mon Jan 12, 2009 3:29 pm ]
Post subject:  1st Top - Bracing Critique
Hi all, I am close to finishing my first top and after taking a lot of info from the archives (thank you all!) about bracing and trying to follow Cumpiano's book, I have a braced top that is most likely over-braced. But, let me know what I can do/improve - any advice is very welcome!!

Specs for my OM:
Top Wood - Sitca Spruce (not sure how stiff since this is #1) - .095 at edges, .105 in center
X-bracing - 5/16" thick x .700" tall at cross, 1/8" at lining, .600" at scallop peak
U. Face Brace - 1/2" wide x 5/8" high, I plane to drill truss rod hole later
U. Trans. Grft - 7/8" x 1/8"
L. Face braces - 1/4" wide x 5/8" at peak
Finger Braces - 1/4" wide x 1/4" at peak
SH Braces - 5/16" wide x 3/8" at peak
Bridge patch - .085" thick, IRW
Bracing is all sitca and is better quartersawn than top... Too bad for top...:(

I am worried that:
The Xbrace intersection is still too high maybe?
Xbraces are too beefy since they started out at 5/16" instead of 1/4"
The Lower face braces (tone bars??) are to "chubby" and need to be more triangular in x-sect
I think I need a graft over Xbrace intersection (although I am happy with joint)

Thank you guys so much for your help. I know you see a lot of this, but it is tremendously helpful I think.
Author:  justink [ Mon Jan 12, 2009 3:33 pm ]
Post subject:  Re: 1st Top - Bracing Critique
Oh, forgot...
As far as tap tuning, I tried a bit (but really have no idea what to look for)
I only get a "thud" sound when I hold it between thumb and finger at Upperface brace and side interstection and tap on upper face brace just above sound hole. Everywhere else it resonates to some extent but not for too long. It rings a lot better when I just suspend it from 1 finger at sound hole.

How long of sustain do you look for? (roughly.... 1, 2, 3, 12 seconds??)
thanks guys
Author:  Alexandru Marian [ Mon Jan 12, 2009 5:46 pm ]
Post subject:  Re: 1st Top - Bracing Critique
Looks quite good for a 1st. You should maybe cap the X, and I would extended the edge rounding all the way to the intersection. Peaks look kind of too sharp compared to what I have seen before.
Author:  Hesh [ Mon Jan 12, 2009 6:04 pm ]
Post subject:  Re: 1st Top - Bracing Critique
Nice job Justin!!! [:Y:] [clap] [clap] [clap] [clap] [clap]

OK here are some things that I see and I am sure others will weigh-in too.

For an OM sized guitar I use 1/4" wide braces and my height at the X intersection is no more than 1/2". Your height at the intersection is a bit high IMHO.

The joint does look excellent - pat yourself on the back my friend and once you have the final height be sure to install that piece of 1/32 - 1/16" thick spruce cap over the X intersection.

Your scallops look a bit odd to me and almost more like tapered/parabolic braces with a horn on them. I think where you are starting the scallop is too close to the X-intersection but the good news is that you barely scalloped at all and the brace height at the X intersection is high so you have more than enough to work with from here.

Since the braces started life a bit wide, 5/8" you could remove more material from the sides to try to get a sharper triangular cross section and nix some brace mass at the same time. Also if you go with a X-intersection of 1/2" or .550 you will see that some of the peaks can be lower and less massive too.

As for voicing even though you don't know what to listen for yet you will very shortly. Start off with the top facing you and find the half way point on the left side. Note this point and now from the middle of the top to the top of the top find the mid way point. You now have a point along the left side 1/4 of the height of the top down from the top. This is where you want to hold the top between two fingers, close to the edge, while taping. There are other places too but let's find this one first.

Now the idea is to tap all over the top and listen. You will hear either a dead thud or a slight ringing. The ringing will have a note to it that will get lower as the mass of the braces is removed and will also come to life from a dead thud as the mass is removed. Sustain times, since this is very difficult to hear, of 3-4 seconds are excellent.

Tap all over the top from the middle of the sound hole down. Note where there is a dead spot and see how it is braced. If you need to make it ring remove mass from the sides of the brace first until you have a triangular cross section. If it still thuds reduce the height of the brace, reprofile, and check your results. Tap tracing the brace paths because this is usually where the dead spots will be. Don't expect to be able to make the X intersection ring well although this can be done.

Intersections of the tone bars and finger braces with the X are usually problematic and can benefit, if it does not ring there, by using a chisel where the finger braces and tone bars butt the X and reduce height.

Be sure to hold the top too with both hands and thumbs on some of the braces and flex it in your hands. What are you looking for? You are developing a feel for the top and in time you will note how much it can flex and what kind of guitar resulted.

Nice job on your first bracing job and with a few tweaks you will have a great sounding guitar. You may also have one now if you just went with what you have.

Lastly don't forget the truss rod hole in the UTB if you are going to adjust your truss from the guitar body.
Author:  Flori F. [ Mon Jan 12, 2009 7:19 pm ]
Post subject:  Re: 1st Top - Bracing Critique
Justin,

It's beautiful work, but as Hesh said, .7 for the x-intersection is quite high on a hand-built OM. Many seem to think .6 to .5 is sufficient. Given that info, .6 at the x-brace scallops' peaks is a little high too, I think. I would also think that 5/8th peaks on Lower Face Braces is pretty high. But it's hard to give a concrete opinion since we don't know how stiff your top is.

John Mayes has a very useful dvd on voicing. I thought the Cumpiano book gave general guidelines on voicing as well.

The other problem is that what you 'should' do with your bracing depends what type of sound you want out of your guitar. Mayes does a nice job of explaining how to get different tones out of your top in his "advanced voicing" dvd.

I'm sure others, who've been building longer, will offer their opinions as well.

Best,

Flori
Author:  Howard Klepper [ Mon Jan 12, 2009 7:40 pm ]
Post subject:  Re: 1st Top - Bracing Critique
You're doing fine. I make the X 5/8"tall at the intersection, and about 9/32 to 5/16 wide. Mine are more like 1/16" where they enter the linings. Do cap the X.

The peaks of the scallops look too tall and sharp to me. But there is a wide range of styles for this among successful builders.

There is a node about 2" in from the edge and maybe 1" above the waist. Grip there with two finger to tap. Move your grip around a bit and you'll find it.
Author:  TonyKarol [ Tue Jan 13, 2009 8:17 am ]
Post subject:  Re: 1st Top - Bracing Critique
On any std 6, I never make the X peak more than .590 ... on an OM, more like .550, or possibly .500 if the player will use only lights ... as for the scallops, cant say, I am a taper kinda guy ...
Author:  justink [ Tue Jan 13, 2009 10:43 am ]
Post subject:  Re: 1st Top - Bracing Critique
Thank you guys so much for the help. I really appreciate it. I know that this first guitar will turn out 100 times better than it would have because of this forum and the help of all you other builders. And Hesh, thank you for the great, lengthy reply and instructions on tap tunning. I am going to give it a shot today and I'll let you guys know how it progresses.

Thanks again for all the advice!
Author:  SteveSmith [ Tue Jan 13, 2009 10:57 am ]
Post subject:  Re: 1st Top - Bracing Critique
Good thread. I thought I was done carving the braces on my first top (sitka on a walnut OM) till I read this. I had pretty-much followed the Mayes Advanced Voicing DVD which recommends an X-brace height of .7". My X-braces are 5/16" so sounds like I need to remove the cap, reduce the height to between .550" and .625", then recap.
Author:  justink [ Tue Jan 13, 2009 11:16 am ]
Post subject:  Re: 1st Top - Bracing Critique
One more question - Do I even need scallops????

As this is my first, I have no reason to use or not use them - I just like the elegant look of the braces when they are scallopped with peaks (silly reason, I know).

But I don't think I have take too much mass off at this point - I could just forget the peaks and taper the X brace legs and tone bars with no scallops...
Author:  Hesh [ Tue Jan 13, 2009 11:20 am ]
Post subject:  Re: 1st Top - Bracing Critique
justink wrote:
One more question - Do I even need scallops????



I was wondering if you were going to ask this question, Justin. :D

Of course I am biased but I use tapered/parabolic braces and don't scallop so if you are asking me I would say that you don't need to scallop. But you still most certainly may if you want to do so - there is enough brace material left for you to do either.

Oh to scallop or not to scallop - that is the question...... :D
Author:  Frei [ Tue Jan 13, 2009 1:25 pm ]
Post subject:  Re: 1st Top - Bracing Critique
Seems to me that the peaks are where the bridge plate is, so your already reinforced there, this may be way too stiff in that area.

The first scallop on the X braces is about 2" from the sides, where, as stated, there is a 'node'. Looks like you can get away with wacking the peaks and going parabolic.

(This is why I gave in and got a 'standard' dred plan. Too much improvising when you know not what you do' is not a good thing here.)

Can you record tapping the top?
Author:  justink [ Tue Jan 13, 2009 2:00 pm ]
Post subject:  Re: 1st Top - Bracing Critique
Frei wrote:
Can you record tapping the top?


Unfortunately, i can't. I don't have any recording equipment.

As for scallops - I think I will just get rid of them, or at least really tone them down and relocate them as I bring the total brace height down. Thank you guys for the help on this.

I understand why you would want scallops (i think theoretically) but I don't really have any knowledge built up as to where I need to stiffen the top, or where I can use them and get away with less material elsewhere. So, maybe save those nice arches for another guitar, down the road...
Author:  Howard Klepper [ Tue Jan 13, 2009 2:02 pm ]
Post subject:  Re: 1st Top - Bracing Critique
Frei wrote:
Seems to me that the peaks are where the bridge plate is, so your already reinforced there, this may be way too stiff in that area.

The first scallop on the X braces is about 2" from the sides, where, as stated, there is a 'node'. Looks like you can get away with wacking the peaks and going parabolic.

(This is why I gave in and got a 'standard' dred plan. Too much improvising when you know not what you do' is not a good thing here.)

Can you record tapping the top?

A few things:

>What I said about a node for tapping has nothing to do with placing any scallop on a brace. The upper arms of the X should not be scalloped.

>The word "parabolic" as applied to guitar bracing is an obfuscating and aggrandizing misuse. No one plots a parabola and uses it as a shape for a brace. All it appears to mean is 'convex.'

>As for the crossing of the X, it's supposed to be rigid. That's why we cap it. It keeps the top from collapsing down into the soundhole. So what harm is an extra 1/8" of height there, which adds quite a bit of rigidity, supposed to cause? It may not be necessary, but I doubt that the 1-2 grams of added weight and stiffness at this area is hurting anything. If you want more flexibility elsewhere, the height of the X arms can be cut where you want it.
Author:  JJ Donohue [ Tue Jan 13, 2009 3:23 pm ]
Post subject:  Re: 1st Top - Bracing Critique
Howard Klepper wrote:

>The word "parabolic" as applied to guitar bracing is an obfuscating and aggrandizing misuse. No one plots a parabola and uses it as a shape for a brace. All it appears to mean is 'convex.'



Finally...a referee throws the flag on this one! [clap] [clap]

So far my list includes:
-kerfing
-parabolic bracing
Author:  justink [ Tue Jan 13, 2009 9:53 pm ]
Post subject:  Re: 1st Top - Bracing Critique
Thank you guys again, for all your help. I feel a lot better about this top now. Ok, here is a little update to my top... With your help, I am maybe closer (I think I am happy with it!)

The X intersection is .565" with a 1/16" cap. I also nixed the peaks on most braces in favor of longer, smoother curves across the length of each brace.

I tapped it a bunch and after finding that "sweet spot" or "node" around the where the upper X leg enters the lining, I got it to ring pretty much everywhere, if only for a short while. I didn't have any 2-3 second sustain, but it did ring for a good 1-1.5 seconds most places. If I just hand it from my thumb in the sound hole it will ring longer than 3 seconds in a lot of the lower areas. It starts as a lower ring and heads toward a higher note as it dies.

I also notices (while tapping) that my back rings better than my top does.... Is this normal/good/bad ?... I am also wondering (judging by the slenderness of my top braces) if my back is way over braced as well. It is pretty heavy.
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