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PostPosted: Sat Mar 25, 2017 7:54 am 
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Hi ,I've had an OM kit from LMI for 0ver 10 years and have decided to get going on it . I already have a quality Acoustic steel string so I want to turn it into a "crossover type guitar " with a cutaway , nylon strings and a Fishman pickup system ala Lowden Jazz and will probably change the top to a Cedar one .I can follow the plans easily but will require a different bracing system which I haven't got a clue about .I know a bit about Guitar construction and have so far built 2 Guitars and 2 Basses but Acoustics are another thing, but I'll get there .So I know most builders have their own ideas about bracing and there are consequently many different types and I know some of the criteria required which effect the construction ,placement ,stiffness ,vibrating top ,projection of sound ,etc but would like to have a definate bracing plan for a Guitar of this sort . So any suggestions would be greatly appreciated .Thanks


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PostPosted: Sat Mar 25, 2017 8:29 am 
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Cedar for sure. Double top would be even better. Soundboard mass is going to be your biggest enemy. OM is really a bit too big for nylon strings, IMO. Design the bridge for minimal weight as well. Padauk might be good. Walnut or even mahogany could potentially work and be even lighter.

Bracing wise, I'd just go with a typical fan bracing arrangement. Big cross brace below the soundhole to set the perimeter of the active area, 7 fan braces, and two diagonal closing braces near the tail. Bridge should be wide enough to catch the second fans from the outside. Possibly could be better to use 8 or 9 fans where the bridge catches the third from outside, so it doesn't need to be so wide.


Last edited by DennisK on Sat Mar 25, 2017 8:39 am, edited 1 time in total.


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PostPosted: Sat Mar 25, 2017 8:33 am 
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A bracing plan that I have used recently which I have been happy with is an X brace/fan combination. The X brace only touches the soundboard at the ends of the brace (near the sides) and at the crossing of the X. The fans are laid out in a normal pattern but pass under the X and extend into the upper bout. My thinking is the "floating X" supports the area most susceptible to collapsing under string tension but still allows the fans to act as fans. I'm using spruce boards and stringing with light gauge steel.
For an OM pattern guitar where you will only be using Nylon strings you may want to modify the typical fan brace layout to suit the slightly wider upper and lower bout. The length of the bodies of the Classical and OM guitars are roughly the same so not a lot of changes would be needed. Fleta used a plantilla that had an upper bout width similar to an OM's and a waist that was wider. The difference in square inches of soundboard of an OM with a cutaway and a large bodied classical may not be that great.
One other suggestion would be to make the OM a 12 fret to the body guitar. That would move the bridge down a little and put it more in classical territory.



These users thanked the author Clay S. for the post: Spino (Sun Mar 26, 2017 12:57 pm)
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PostPosted: Sat Mar 25, 2017 10:47 am 
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I have only built one nylon string guitar and it was the classic 1937 Hauser (that everyone builds). There are many plans available for this and similar guitars, one option is to simply copy one of them. Along with the bracing you may want to thickness the top differently than you would for a steel string. You can also make those changes like f/b radius and width to make it a "cross over".

One of the successfull crossover nylon strung guitars it the Taylor nylon - they discuss the bracing here

https://www.taylorguitars.com/guitars/a ... es/bracing

At one time their website had pictures of various bracing patterns but I can't find it. If you search for "taylor nylon bracing" you'll see some pictures, one is Bob holding a top. Looks to be a very simple five fan with no cutoff bars, angled brace below the sound hole and Taylors "relief route".

Some other things that you may want to change from your OM kit include the neck, bridge, possibly the neck block to fit the cutaway.



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PostPosted: Sat Mar 25, 2017 2:54 pm 
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DennisK wrote:
.... Big cross brace below the soundhole to set the perimeter of the active area, 7 fan braces, and two diagonal closing braces near the tail......


+1
IMO this is an important point/consideration. I might even consider using a hardwood like maple for it.
edit: I,m referring to the 1 transverse brace below the soundhole, not all braces.

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Last edited by Jim Watts on Sat Mar 25, 2017 6:56 pm, edited 1 time in total.


These users thanked the author Jim Watts for the post: Spino (Sun Mar 26, 2017 12:57 pm)
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PostPosted: Sat Mar 25, 2017 6:18 pm 
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Is it a 'serviced kit'? If it is that will cause you some problems going to a classical. Mainly in the area of neck width and scale length. If it is not then you should be good to go. You can pick a bracing pattern that sounds good to your ear. You can even reduce the body somewhat to bring it more in line with classical construction. If you do stay with the larger body then I would consider a long scale such as 660mm. You'll have a better chance of driving the OM air volume.

But then with pickup's most any configuration may work.

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These users thanked the author Joe Beaver for the post: Spino (Sun Mar 26, 2017 12:57 pm)
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PostPosted: Sun Mar 26, 2017 5:22 am 
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Do you know why there are a hundred different bracing patterns for guitar soundboards? It is because all of them work (to a degree). If there was one clearly superior method, we would all know about it and use it exclusively. You are already defying convention here by putting nylon strings on a OM-like body, so you can be as free as you like. Just exercise some reason-based decision making. My few thoughts are provided for your consideration, or derision. I am assuming that you are making this instrument for yourself, so you only need so satisfy your own preferences - not popular opinion, fashion or tradition.

It has already been pointed out that this body is bigger than the usual classical, meaning you will need a slightly stiffer top, and nylon strings have less driving force than steel strings. So weight of the soundboard and bridge are important. Cedar tops tend to need to be a bit thicker and heavier than spruce, to achieve the same stiffness. You might want to choose spruce for that reason. On the other hand, if you are going to play it amplified (you mentioned a pickup), you don't need to build it for maximum volume.

Steel string type bracing will be heavier than you need. You could use the same pattern but lighten it up (thinner, maybe add some carbon fibre capping). No scalloping. Don't tuck them into the sides. With a tie-on bridge you won't need a bridge plate.

Another alternative is falcate bracing. This is used by Trevor Gore in his neo-classical nylon guitars which have a OM sized body, as well as in steel-strings. I recently built a falcate braced nylon using a Gibson L-00 body shape. It is the first nylon I have ever built so I hesitate to offer an opinion about it versus traditional classical bracing. But if you are doing something "modern" it is a fun variant. Trevor has done very extensive research of the performance of CF-capped falcate bracing versus many traditional bracing patterns. It works well for nylons. If you are interested there is lots of information to read about it online (especially at the anzlf - we Aussies have been early adopters).

If you are free of the requirements of traditional design I have three words to say - bolt on neck. But you asked about bracing so lets not go there.

One of the great things about building your own guitar is that you can have fun with it, and make something different from the stuff hanging on the wall down at Guitar Center, or wherever. Whatever you do - enjoy the process and learn something. It probably won't be the last instrument you build. Nobody stops after five!
Cheers
Mark



These users thanked the author Mark Mc for the post: Spino (Sun Mar 26, 2017 12:57 pm)
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PostPosted: Sun Mar 26, 2017 9:06 am 
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Mark Mc wrote:
It has already been pointed out that this body is bigger than the usual classical, meaning you will need a slightly stiffer top, and nylon strings have less driving force than steel strings. So weight of the soundboard and bridge are important. Cedar tops tend to need to be a bit thicker and heavier than spruce, to achieve the same stiffness. You might want to choose spruce for that reason. On the other hand, if you are going to play it amplified (you mentioned a pickup), you don't need to build it for maximum volume.

Thicker, yes, but cedar's density is so low that it should still be slightly lighter than spruce for a given stiffness. About 4% lighter by my calculations. Or if you make them equal weight, the cedar will be 12% stiffer (and about 17% thicker).

Technically cedar would make lighter braces as well, but it's not so good for that because of its low strength in a situation where a lot of stress is concentrated onto a small amount of wood (long term deformation will happen faster). Spruce is pretty much always the right choice for braces.



These users thanked the author DennisK for the post: Spino (Sun Mar 26, 2017 12:57 pm)
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PostPosted: Sun Mar 26, 2017 1:55 pm 
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Thanks Dennis. I stand corrected.
mm


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PostPosted: Sun Mar 26, 2017 3:57 pm 
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I've made a couple of 12-fret 000s for nylon strings that were quite successful. The OM is simply the 14-fret version of that, so I see no reason why it would not work. Keep in mind that when Martin cooked up that design they were thinking of gut strings. Of course, the early ones were not built as heavily as a modern steel string, and that's really the main issue.

I agree that the OM/000 size would probably be too big for nylon strings if you braced it like a Spanish Classical guitar, with fan bracing. At the same time, X-braced nylon string guitars don't work as well as fan braced ones, because they're too small. X-bracing is structurally a bit more efficient; you end up with more stiffness where you need it, between the bridge and the sound hole, so you can lighten up on the top and bracing somewhat. This gets the weight down, and improves the ratio of top area to mass; what Gore calls 'monopole mobility', which basically is a measure of potential power.

Of course, it helps to use a low density top. On softwoods the Young's modulus along the grain (Elong, which predicts stiffness at a given thickness) tracks density pretty well. The relationship between Elong and density is pretty much linear in the range of densities we see. Since stiffness varies as the Young's modulus and the cube of the thickness, you can leave a low density top a bit thicker to get the stiffness up and still end up with a lighter top. I used Red spruce of 'average' density for the first 000 Classical I made, and the top was a bit heavier than my usual Standard Classical, although not much. Using a lower density piece of WRC for the second got the top weight down below the average for the Classicals I'd made before that; a reflection of the higher efficiency of the X bracing. Since wood varies a lot in density and Elong I won't give you a number for the thickness. If you make the nylon string top about 85% as thick as you would if you were making a steel string with the same top, that should work OK, although it's always better to make that sort of decision based on real numbers. Since most of the weight of the top is in the top itself, you can see that you've shaved a fair amount off there.

I used 1/4" wide spruce bracing on both of those 000s, and, again, reduced the height by about 15% from what I'd have used on a steel string the same size. The bracing usually amounts to something like 25%-30% of the total top weight, so you're not saving a lot there, but every little bit helps.

Although Martin followed German and French practice and used a pin bridge for their gut strung guitars, I elected to go with a Spanish style tieblock, and I'd recommend that strongly. If you use a pin bridge some idiot will try to put heavy gauge steel strings on in and rip the top off. I did use a small bridge patch of spruce on mine, even though it's not needed to keep the string ends from chewing up the top. With the wider span between braces it helps to keep the belly in back down. The bridge weight should be less than 25grams, and 20 is nice if you can do it.

The B&S will be pretty much the same as on a steel string. You'll use a different neck angle, since the action needs to be higher, and don't make the nut too narrow. Very time I've made a nylon string guitar with a nut narrower than 1-3/4" (at customer insistence) they come back a few months later asking if it can be enlarged. That's hard. You can always carve the neck down if it's too wide (unless you used a bound fingerboard...), but enlarging one is no fun.

Properly done what you're talking about has a lot of potential. It's harder to make a good Classical than a good steel string, of course. It's not so much that nylon strings don't have the energy to drive the top: the tension is lower, but they generally pretty much make up for that with the higher action. The problem is that there's not much high frequency energy in the strings, due to the higher damping ofnylon as a material, and the fact that the fatter strings need to move more air, which also adds damping. Making a good steel string is a matter of getting enough low end to balance the highs in the strings, and that's relatively easily done by making the box bigger. With a nylon strung guitar you have to make the most out of the little bit of high frequency the strings can give you, and that's a matter of getting the top to work well. Pay attention to the 'tap tones' as you trim the braces down, listening for lots of 'clear' and 'full' tap tones. You're looking for the 'right' balance between the braces and the top itself, and that's going to depend on a lot of variables.


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PostPosted: Sun Mar 26, 2017 4:35 pm 
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I've only constructed one -- for my personal use, so of course its not completed yet. Custom 14th fret bolt on neck, 1-3/4" at the nut, classical spacing at the bridge. 25.34 scale length. Spruce sound board .095", Standard Torres bracing outter fans just a tad thicker than the rest. The face of the sound board is beveled on the lower bout perimeter to 1" inboard, tapered to about 1/16" on the edge.

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PostPosted: Sun Mar 26, 2017 6:25 pm 
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That's a real beauty Ken. Looking forward to final impressions.

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PostPosted: Mon Mar 27, 2017 2:18 am 
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You can make the top thinner if you lattice brace it.

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PostPosted: Mon Mar 27, 2017 1:08 pm 
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I picked up the Taylor crossover to try it out. It was awful, I couldn't put it down fast enough. Yuck. Don't use it as an example to follow.

Listen to Alan.

The O size is the one most similar to classical guitars. IF you want to make it more OM sized, look to what builders of large bodied classical guitars are doing. Fleta would be where I look first.

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PostPosted: Mon Mar 27, 2017 2:15 pm 
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Well there you go -- I've played several 400 series and above Taylor cross overs and liked them a lot both amplified and not. Never played the $950 import version so I can't comment.

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PostPosted: Mon Mar 27, 2017 7:31 pm 
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Perfect time to do an arm bevel. Reduces the top area.


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PostPosted: Mon Mar 27, 2017 9:41 pm 
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kencierp wrote:
Well there you go -- I've played several 400 series and above Taylor cross overs and liked them a lot both amplified and not. Never played the $950 import version so I can't comment.


Yep! Opinions all over the place!

I can't remember which ones I played, it was over a year or two ago. I was just looking at the Taylor site and they have many more versions now.

The two that I played I found to be heavy and the sound was meh. Other models may be better, who knows.

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PostPosted: Mon Mar 27, 2017 11:25 pm 
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I read up on the Fleta that Douglas mentioned. Seems he built near OM size classicals in the 70's that are still considered world class. And they are fan braced. Very impressive

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PostPosted: Tue Mar 28, 2017 11:38 am 
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"The O size is the one most similar to classical guitars"

Just as a point of interest it is the 12 fret OO size that is the most similar to the classical dimensionally (OO has a smaller upper bout than classical but same 14 inch lower bout)
A plan for the Fleta guitar Doug and I mentioned can be found in Courtnall's "Making Master Guitars" book. He made a fair number of cedar topped guitars.


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PostPosted: Tue Mar 28, 2017 11:56 am 
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LMI has a plan for a 1968 Ignacio Fleta. Any feedback?

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PostPosted: Tue Mar 28, 2017 12:00 pm 
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My take on the crossover design concept is that the player can comfortably, on the fly transition from a steel string instrument to a nylon string string and easily take advantage of the unique sound pallet that is offered. A classical guitar with its 2 1/8" (sometimes more) neck and finger board makes this difficult for some of us. I fully intend to play mine amplified most of the time -- with effects, EQ and all. So I have no need or intention of trying to mimic one of the great classical guitars/builders. Play-ability is key.

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PostPosted: Tue Mar 28, 2017 2:35 pm 
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Clay S. wrote:
"The O size is the one most similar to classical guitars"

Just as a point of interest it is the 12 fret OO size that is the most similar to the classical dimensionally (OO has a smaller upper bout than classical but same 14 inch lower bout)
A plan for the Fleta guitar Doug and I mentioned can be found in Courtnall's "Making Master Guitars" book. He made a fair number of cedar topped guitars.


Depends upon which classical plantilla you are comparing to as there is tremendous variety. I favour the FE Torres size guitars. The 0 size is very close to the FE19.

The earlier classical guitar also had a much narrower nut than many do today. The typical Torres nut was 49mm. The wide nuts that many people are challenged by became the norm after Segovia and his big hands encouraged a new norm. 2 1/8" works out to 53mm which is exceptionally wide for a classical guitar.

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PostPosted: Tue Mar 28, 2017 2:40 pm 
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Joe Beaver wrote:
LMI has a plan for a 1968 Ignacio Fleta. Any feedback?


Those are the plans from the Courtnall book and could be considered as a typical design for what Fleta has been known for. If I were making a classical guitar on a large bodied plantilla similar to an OM, I would consider this as an excellent starting point.

For $12.50, how could you go wrong?

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PostPosted: Tue Mar 28, 2017 5:38 pm 
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Thanks Douglas, I just ordered it. It may be next year before I get a chance to make another classical but I do like study time, and a larger bodied classical has been rattling around in the back of my head for some time.

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PostPosted: Tue Mar 28, 2017 8:39 pm 
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Martin O size 13.5in low bout. Torres FE19 13.8 low bout, Martin OO size 14.1 low bout.

I also like building small bodied guitars, but most modern guitars, both steel string and classical, have grown in size over the years.


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