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Discussion in 'Tele Home Depot' started by Freeman Keller, Aug 7, 2019.
Here is checking one of the 25 foot braces against the master sheet metal template from the laser
Hat's off to you Freeman!!!! Thanks for this comprehensive tutorial ...............you'll do me for a qualified luthier any day!
Added the bridge plate. Another one of those design decisions - old Martins and most other guitars had pretty small bridge plates, often made from scrap rosewood or maple. After the war bridge plates got bigger, usually rosewood and some feel they are part of the reason the old guitars sound better. Mine is a small piece of maple, I've sanded it to fit the top radius and tucked it up between the legs of the X.
Added some little pieces of spruce across the grain of the soundhole. Soundhole is a pretty highly stressed area, but those braces will just get in the way if I ever want to install a soundhole preamp. Probably won't so in they go.
Today we'll glue the rest of the braces in place. Tone bars and finger braces
and a little cap on the crossing of the X
Very inspiring! If I may ask, would a Martin bracing design work with a classical guitar ?
It did for many years.Martin did X bracing long before introducing steel strings
I am far from being an expert on classical guitars - I have built exactly one (in the true classical fashion) but there is no reason that is shouldn't work. Some things to consider - a nylon string guitar has right at 100 pounds of string tension, a steel string guitar has somewhere between 165 and 180 - it varies with gauge, scale and tuning, so you don't have nearly the shear or rotational torques on the the top. The actual thickness of the tops are pretty similar but the classical wants it to be a lot less stiff. I would think that you would want to radically reduce the size of the braces (we will be talking about that soon when I start carving them). Most classicals use a tie block bridge design, however a few have pins - either way the approach to the bridge plate and the forces in that area would be different.
It is also interesting to me that while we tend to think of classical guitars as being fairly stuck in their history - Torres and Houser and all the other great builders, there is a small group of modern luthiers who are really pushing the envelope of materials and designs - double tops with Nomex layers, lattice bracing and all kinds of weird and wacky designs. While I don't see these guys using X braces very much companies like Taylor and Yamaha and Cordoba have made X braced guitars that are intended for steel string players who want that nylon sound.
Lastly, I know that Paul Reed Smith uses fan braces between the legs of the X in his steel string guitars instead of the tone bars.
So, yes, it would probably work but would require a bit of thought to make it work really well.
I want to say that Willie's N-20 is X braced but I'm not sure. However Trigger might be nylon strung but its a stretch to call it a classical LOL
Trigger is a special beast. That's for certain!
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I'm enjoying this as I have done a few parts guitars, but the expense of buying the tools to make anything from scratch is daunting to me, btw imho the most important tool seen above on your work bench is the expresso machine.
The espresso machine serves two functions - I can make a nice Americano if I need a little jolt of caffeine or I can shoot a little steam into a dovetail joint if I need to take it apart.
OK, this next part is kind of fun. But it needs a bit of explanation before we dive into voicing the top (you knew this was coming didn't you?).
We have already said that the top is a compromise between two structural requirements - it must be flexible enough to vibrate yet stiff and strong enough to not blow apart under 175 pounds of string tension. It has another requirement too, it must vibrate in such a way as to produce attractive and interesting sounding notes at many different frequencies - ideally all of the notes from a low E or D2 at somewhere around 70 hz to high notes approaching 700 hz. The many shapes and "modes" that the top needs to be able to vibrate in have been well studied but I think still poorly understood.
I certainly don't pretend to understand it, but with each guitar I learn a little more. If we think of the guitar's top as an engineered structure (I'm an anal engineer) then the braces are little beams. From freshman engineering theory we know that the strength and stiffness of a beam (they are not the same but are related) is directly proportional to its width, but proportional to the cube of its height. That means if you make a beam twice as wide it will be twice as stiff, but if you make it twice as tall you make it eight times stiffer. Or another way, if you make it have as wide it is half as stiff, but reduce its height by one half and it is only one eight as stiff. Thats why bridge beams are vertical and floor joists in your house are set on edge.
For the braces in our guitar it means that we can make them wide enough to get a good glue foot print - 1/2 to 5/16 works pretty well - and then make small changes by thinning them or large changes by lowering them. We leave them tall at the sound hole and the area of the bridge and then taper them towards the edges of the top where we want flexibility and movement.
I'm not smart enough to figure all this out and certainly the math is very complex if you want to try to analyze it. What I do, once again, is cheat. I've played a lot of guitars with a certain shape to their braces (if lots of people do it then it must be pretty good) and I like their sound. Therefore I try to emulate that with the hope that mine will sound as good. So far it has worked pretty well.
Every book on acoustic guitar building will have a chapter on "voicing" the top. I've attended three different seminars by three different highly respected builders and each of them does things a little different. I've read books on building "responsive guitars" with very highly theoretical methods of getting the best sound out of a piece of spruce with a few small beams glued to it. I won't pretend to understand any of it.
However, in a nutshell here is what each of these people are doing. The remove wood from the braces in select locations while they tap and flex and otherwise move the top to see what the effect is. In most cases they are listening for the tap sound to "become more musical" (boy, there is an esoteric expression) or maybe they want the tone that comes back to be a certain note. Anyway, they tap and flex and take wood away and tap and flex some more. At some point they stop.
That in a nutshell is voicing the top. Clear as mud, eh?
So here we go. Here is the top with the raw braces. I chose 5/16 because I knew I was going to scallop them - if I had felt that I didn't want to scallop I probably would have made them 1/4.
Start by tapering the braces to a rounded point on top and beveling the tone bars and finger braces where they approach the X
Start taper the ends of each brace where it approaches the rim. The X, UTB and tone bars will be let into notches in the kerfing, the finger brace and popsicle will not.
Starting to scallop - removing material from the height of the X and tone bars. The shape is time honored - I just follow what I've seen before.
At this point I really am trying to tap the top and hear a difference as I remove material. Mostly I hold it vertically at the upper bout and tap over the bridge plate, altho I also move around the lower bout, tapping with my knuckles and listening to the sound.
At some point I say "that's enough" and move it to the back of the work bench
Interestingly in that last picture you can see how the edge curves up from the workbench as a result of the dome built into the braces.
This is fantastic! Thank you for this outstanding thread. Your work and your way of explaining things are both exceptional!
> I'm an anal engineer
You might want to rephrase that statement! LOL
Scalloped 1/4" bracing is anything but problematic .
Back bracing is a lot easier to understand and execute that the top. It has three functions - it maintains the 15 foot radius of the back doming from side to side (end to end will be a matter of how the sides are arched), it provides cross grain support for the back itself, and, while I personally don't think the back is very active in making sound, I give it the benefit of doubt and make it a little looser around the rim. Oh, and since you can see the back braces thru the sound hole they have to look nice
I sanded the top edge of the rim to receive the top - it would have been better to do it in a radius dish but since I don't have one for the top I first made it flat, then took the caul and just knocked the kerfing back a bit. Its important to get the little angle sanded into the neck and tail blocks
Notched the kerfing to receive the ends of the braces
And here we have three of the five sub assemblies
Signed and dated the top
A little glue around the rim
And into the go-bar deck it goes
Like so many things in lutherie, there are several different ways to clamp the top and back while gluing. It takes a lot of clamps to distribute the pressure all the way around. Some people make little spool clamps out of a piece of all thread rod, some little wooden spools and wing nuts. The problem with spool clamps or even a bunch of little Irvin clamps is that you can't do it with the sides in the mold and there is a possibility of introducing a twist to the sides. The go-bars work pretty well as long as I put lots of little blocks of wood under them to distribute pressure.
Wow! This thread is way too cool. Thanks for sharing Freeman.
@Freeman Keller : Thank you so much for all of this. Most appreciative of the time you've taken and the details of construction. This is an amazing thread, and part of what makes TDPRI unique.
One small question: the date on the reverse of the top? 6+ years ago? Am I missing something?
No, in the introduction I said that I was putting together a thread for a friend who wanted to know what was involved in building an acoustic. The guitar has been done for several years and he has played it. However I'm more or less documenting it exactly if it was currently on my workbench. I think I asked at the beginning if this was legit - didn't get any complaints so here it is.
I had considered just putting the pictures and text in a Word document and giving it to him but figured that it would be no more work to just share with the community.