Need Advice on build #3 & 4

[dandenson]

I am building a pair of parlor guitars from Scott Antes plans for Christmas presents (2011, probably). The back and sides will be some walnut I re-sawed. I have some sitka spruce on hand, but wonder if red cedar might sound better. I am trying to keep the price down using woods and materials I have on hand as much as possible.

My first build was a StuMac dred, and my second was an unserviced LMI small jumbo. What allowances, if any, do you make in top thickness and bracing for a small guitar versus a large one?

Thanks,
Dan

[Freeman]

I am building a pair of parlor guitars from Scott Antes plans for Christmas presents (2011, probably). The back and sides will be some walnut I re-sawed. I have some sitka spruce on hand, but wonder if red cedar might sound better. I am trying to keep the price down using woods and materials I have on hand as much as possible.

My first build was a StuMac dred, and my second was an unserviced LMI small jumbo. What allowances, if any, do you make in top thickness and bracing for a small guitar versus a large one?

Thanks,
Dan

Remember that the Antes plans are drawn as tho you were looking thru the top, not at the back of the top (as is usual). It is pretty easy to get the tone bar (one in the case of the parlor) on bass-ackwards (you'll make it a lefty, ask how I know). Also Scotts' plans are often called "over built" - you might want to consider being fairly aggressive with your top voicing.

I built one for my daughter, based roughly on an 0-42, out of sitka and rosewood. It is a boxy bluesy sounding little guitar, remarkably loud for its size. I know that a pyramid bridge would have looked "correct" but I liked the cut down belly bridge.

http://www.kitguitarsforum.com/archives ... 28_0_9_0_C

I use the same top thickness for everything except 12 strings (where I go about 10-15% thicker and add a tone bar). I normally scallop fairly aggressively, trying my amature best to flex and tap on the top as I do so. I have been told that my guitars (all small bodies - 0, 000, OM) are very "responsive" and they haven't imploded yet.

[tippie53]

Agree that the antes plan is just way overbraced. use a 5/16 brace width and 5/8 height. If you do scallop take about 1/3 off. That will get you close . Sitka will be just fine

[Darryl Young]

I am building a pair of parlor guitars from Scott Antes plans for Christmas presents (2011, probably). The back and sides will be some walnut I re-sawed. I have some sitka spruce on hand, but wonder if red cedar might sound better. I am trying to keep the price down using woods and materials I have on hand as much as possible.

My first build was a StuMac dred, and my second was an unserviced LMI small jumbo. What allowances, if any, do you make in top thickness and bracing for a small guitar versus a large one?

That is a great question Dan! I wish I knew the answer. I'm going to throw out a few thoughts for discussion. This approach is more from a mechanical view.....not from experience building guitars.....so give the advice from experienced builders preference.

Do you want the top on a small guitar to flex similar to a top on a large guitar with string vibration? That seems logical to me. Assume the same scale length is used on a large and small guitar. The pull of the strings terminates at the bridge which is fairly close to the center of the lower bout. To average everything out, seems you could look at the distance from the center of the bridge to the edge of the guitar body to find the moment arm. Likely the distance from the bridge center to the bottom of the lower bout will be a little different than from the center of the bridge to the sides of the lower bout but for this discussion, consider only the distance from the bridge center to the bottom of the lower bout.

The moment (M) equals the the Force (F) multiplied by the Length (L) of the moment arm (so M=FxL). So if the top on both the large and small tops were identical, then creating the same moment should let the two tops flex similarly. On a dreadnaught, the distance from the saddle to the lower bout is 8.712". Subtract 0.01" for string compensation and you have 8.612". For a 00 sized guitar, the compensated distance is 7.487"......so the 00 moment arm is 87% the length of the dreadnaught moment arm. The Force (F) comes from the pull of the strings so should be identical on both guitars if the same gauge strings are used.

So if the tops for the dreadnaught and the 00 were identical and if you want the tops to flex the same, seems you would want only 87% of the stiffness in a 00 top that you have in a dreadnaught top. Stiffness goes up with the cube of the height. So if your dreadnaught top was 0.125" thick, cube that value and you get 0.001953. Now take 87% of that value and you get 0.001699. Now take the cube root of 0.001699 and you get a thickness for the 00 top of 0.119" thick and it should have the same flex in a 00 body as the thicker top had on the dreadnaught body.

That's just my thoughts.

[kencierp]

Its really difficult to make a mistake when building a guitar -- we all pretty much look to the basic formulas. I suggest that you don't get all wrapped up in a bunch of numbers some guy may have pulled out of his butt (where's the data comparing of all the completed guitars?). Generally the thought has always been to build them as lightly as possible (within reason). Some say to the point where the instrument is on the verge of implosion.

I agree with John Hall, the Scott Andez plans all have brace dimensions that are way too heavy. Just to be clear, note that Martin sells Dreads and M/J models -- big guitars that have 5/16" or 1/4" bracing both offered scalloped and unscalloped. So the worry about light bracing and structure is a non issue. Cedar -- Sitka -- Englemann -- Redwood, matters not, they all will sound just fine with the normal individual nuances, they are what they are!! For me thinning most tops down to .095 -.100 works good. Most importantly -- if a guitar after it is built seems a bit tight --- just change the gage of a few or all of the strings and the personality of the instrument will change as well.

[Tony_in_NYC]

Dang Darryl! You want me to do math? I just want to make guitars! LOL Although, what you say makes sense....the only problem is that each piece of wood is different, so it sort of messes up any calculations. But, thats a good starting point.
I have a Magic 8 Ball I use to determine if my bracing is good. It has worked so far. But I do get annoyed when it gets stuck on "The answer is...No" because I fear it may be wrong and I might over carve my braces.

[kencierp]

If you read the reviews of Ervin Somogyi's million dollars a set publication you'll note that the reviewers point out there is not one mathematical formula to be found!! And the bottom line is --- he build's based on his personal belief system -- pretty much like the rest of us. Don't get me wrong there's plenty to be learned from his writings.

[Tony_in_NYC]

If you read the reviews of Ervin Somogyi's million dollars a set publication you'll note that the reviewers point out there is not one mathematical formula to be found!! And the bottom line is --- he build's based on his personal belief system -- pretty much like the rest of us. Don't get me wrong there's plenty to be learned from his writings.

Somogyi lowered the price of his books?

For what its worth, the only calculation I care about when building is the neck set angle. I am not a professional luthier doing this for a living so I dont need to compete with real builders. I just need to make a guitar that sounds good to me.
To get back to Dan Denson's question though, a smaller guitar should probably be braced lighter and have a slightly thinner top. But, I can not measure the thickness of my tops since I dont have a caliper. I am a pretty crappy builder. LOL

[tippie53]

I think most of the really good luthiers have some secrets but that all came from experience and learning more what not to do. One thing I feel helped me is using a deflection test to see the strength of the wood so I know how thick or thin and how I need to brace it .
To get repeatability in a process means you have the process controlled . Learn how to control your building processes . Not always an easy task .

[naccoachbob]

If you read the reviews of Ervin Somogyi's million dollars a set publication you'll note that the reviewers point out there is not one mathematical formula to be found!! And the bottom line is --- he build's based on his personal belief system -- pretty much like the rest of us. Don't get me wrong there's plenty to be learned from his writings.

Somogyi lowered the price of his books?

I guarantee he DID NOT lower his price!!!