Fan brace join

Well here's a stupid question that has been bothering me for a while: Is there any logic to whether or not the fan braces butt up tight to the (I think the proper term is) transverse brace? The Hana Lima plans show them butting up, but at least one picture in the construction manual shows a gap between them. I seem to remember Sequoia pointing out to another builder that he should have left space there. What do most builders do, and why?

Thanks,

Nelson

Seems if the fan braces butt up to a cross brace, it could lead to some vibration buzzes there. If you glue the fan ends to the cross brace, it could make the soundboard lower bout too stiff.

I think you will find variations in practice. All will probably taper the ends of the fans: some builders will have fans that almost touch the cross brace and in other cases the fans will fall short. Some builders have a couple of fans which continue along the sides of the soundhole passing through cutouts in the lower cross brace. I haven't noticed anyone gluing the fans to the cross brace but who knows?

In my case if I use 3 fans they will be approx 5 mm short of the cross brace. If I use 5 fans, the 2 outer ones will be shorter so may be 20 or 25 mm short of the cross brace.

I think its simply a question of what works for each builder: they decide on top thickness, type of kerfing, whether to use a bridge patch, the number and dimensions of their braces, and how they subsequently carve them. Some will carry out some kind of deflection test, some will tap the completed soundboard, some will try flexing it...... to decide whether they have got it right.

Doc_J said:

Seems if the fan braces butt up to a cross brace, it could lead to some vibration buzzes there. If you glue the fan ends to the cross brace, it could make the soundboard lower bout too stiff.

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I think this is a valid question. I'm not an engineer, but it is obvious to me that locking the central fan brace to the transverse brace creates a much stronger structure in an area that is prone to distortion by rotational forces. On the flip side, I could see how it would decrease top vibration and make an over stiff soundboard which would decrease volume and sustain. For this reason I don't do it. We are building musical instruments here, not houses.

If I did make the connection, I wouldn't just do a butt joint. Butt joints as we all know are weak. I would make a shallow mortise in the transverse brace (maybe 2 or 3 mm deep) and make a small mortise/tenon type joint. A simple operation with soft spruce and a sharp knife. This would really lock the fan brace and if you are going to connect them, do it right.

Again, it seems to come down to a compromise between structural integrity versus vibrational latitude. Usually structure trumps latitude because if thang doesn't stay together, than no amount of soundboard vibration matters. On the other hand, if the instrument is so solid it sounds like crap, what is the point?

Here is a thought: What if connecting the fan brace transfers energy into the lower transverse brace distributing the string energy more evenly and making a better sounding uke while at the same time eliminating bellying issues? Could happen I suppose, but I'm not brave enough to try.

On my Sopranos there are no fan braces just the long bridge patch and two transverse braces at the sound hole..on the Concerts 2 fan braces and on Tenors 3 fan braces...the way I look at it is, If all the soundboards are the same thickness then the larger lower bout areas will need some bracing to prevent warping..so it will need a light but strong structure built like a frame all connected together to support the top..so I glue it all together like a spiders web butt joints and all running outwards and tapering down to the linings...But thats just me copying what i've observed in other instruments that work well.

It all comes down to making sure the area in front of the bridge doesn't dip.

Some notch the fans into the transverse brace for extra strength.

There is no right or wrong way to do it. The only wrong thing is to let the top dip in front of the bridge.

Beau Hannam Ukuleles said:

There is no right or wrong way to do it. The only wrong thing is to let the top dip in front of the bridge.

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I'm watching my newest uke and over a couple weeks the bridge has rotated a tiny, tiny bit. I would estimate 1 or 2 degrees. However, short of making a kevlar top or locking the bridge down as discussed, rotation is going to happen no matter how small. Currently the dip is so small as to be irrelevant (changes in compensation are less than 1/64th of an inch and probably much less). However, how about 5, 10, 20 years down the line? I'm optimistic that rotation initially happens and then reaches stability quickly as the uke settles in and will not be an issue down the line. But it does make a guy think.

One way to minimize rotation is to really lock the fan brace at the heel end. The whole thing is like a tetter-totter with the bridge as the fulcrum. If you lock the heel end, then the sound hole end can not move as much. Thus the tiny patch that connects and strengthens the top between the central fan brace and the heel block. This helps prevent the south end fan brace from pulling up and keeps the north end from pulling down. A very small cross grain patch does the trick and does not interfere with top vibration like a notched and locked transverse brace/fan brace connection.

Anyway, my thoughts on a potentially very important question. I did not think this idea up and some builders use this idea to counteract rotation. I think Gordon at Mya-Moe uses a similar idea. Or has in the past. Think I saw it on a video.

A tiny bit of dipping in front of the bridge is ok, as long as it doesn't continue.

Some belly behind the bridge is desirable.

The heel end- you mean the end block at the butt?? - that method sounds faulty to me.
Yes it would minimise rotation, but you lock up the middle so much as to minimize vibration in prime real estate.
My braces stop .5-1" away from the lining in order to do the exact opposite to this AND i thin the top around the lower bout perimeter which further goes away from this principle.

Better just to make everything in front of the bridge solid.

Beau Hannam Ukuleles said:

The heel end- you mean the end block at the butt?? - that method sounds faulty to me.
Yes it would minimise rotation, but you lock up the middle so much as to minimize vibration in prime real estate.

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Yes, I meant locking to the end block. Hey it was just a thought. I would never do it anymore than I would lock the front end of the brace to the transverse brace. Just an idea I wanted to float. I have never seen anyone do this. Cleat yes. Locking notch never. I really believe that the bridge and that real estate needs to be a free as possible. And yet my structural instincts go... hmmm. I'm still feeling my way along and watching the effects of string stress on my tops. So far so good... but down the line. I wonder. Oh, and I don't want to go to X-bracing which addresses this problem.

Some very helpful responses. Thanks. I have been radiusing the lower bout and sanding the upper bout flat in the method described by Chuck Moore. I think leaving a little space between the transverse brace and the fan braces might also ease the soundboard transition from radiused to flat. Think I'll give it a try.

Nelson

If you want to stop any dipping or bulging of the top, arch the top slightly with the dish method or a slight arch from side to side in the lower bout. It doesn't take much arch but some will help.

sequoia said:

Yes, I meant locking to the end block. Hey it was just a thought. I would never do it anymore than I would lock the front end of the brace to the transverse brace. Just an idea I wanted to float. I have never seen anyone do this. Cleat yes. Locking notch never. I really believe that the bridge and that real estate needs to be a free as possible. And yet my structural instincts go... hmmm. I'm still feeling my way along and watching the effects of string stress on my tops. So far so good... but down the line. I wonder. Oh, and I don't want to go to X-bracing which addresses this problem.

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I would say the main thing is to tuck in/ lock in the upper and lower transverse brace into the linings (and dont be afraid to use fatter braces for these braces). If you have that, you are probably fine. if you dont tuck in the upper and lower transverse braces and all the back braces, you are probably smoking crack.

(I played an amazing Pepe Romano Jr uke (tenor?) at HMS which had no back braces)

Beau Hannam Ukuleles said:

if you dont tuck in the upper and lower transverse braces and all the back braces, you are probably smoking crack.

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Well Beau I'm not smoking crack, however I do smoke other things. But here is the thing in my possibly addled brain, "tucking in" any brace seems to me to be a weak join. I actually do tuck in my braces under the linings and against the sides, but really, these are not very strong joints. And if serious twisting or deformation is going to take place over the years I don't think these "tucking in" joints are going to make a difference. I've abandoned the practice and now let my tops and backs float free. Pete once said that this is against "good lutheie practice" and in a way I agree. The only joins I've seen that make structural sense just seem to kill the movement and result in very stable ukes that sound like... well...s**. I'm sorry. I'm still trying to work out this very important part of building great sounding instruments and I struggle. Tight, tight, tight, loose, loose, loose. There has to be a sweet spot in between there somewhere. Onward! Into the fog~

Why is it a weak join? Seems to me to be perfectly adequate for what it's meant to do i.e. support the end of the brace. It's both a glued and a mechanical joint. A floating brace will probably be fine but is obviously more susceptible if the instrument happens to take a sudden knock. That's the time when most braces suffer some sort of failure. A floating brace is also more vulnerable to sudden changes in humidity. Quite often on old instruments (that had floating braces) they would glue in a patch of parchment that would cover the end of the brace, presumably to strengthen an area that they considered to be a weakness. They were obviously aware of the problem. As for the soundboard deformation: it's perfectly normal, in virtually every single stringed instrument known. I suspect that people are far too concerned with structural issues of soundboards. Torres was building soundboards that weren't much more than 1.5 mm's thick on a plantilla far larger than any Uke and with a string tension far greater than on any Uke. After 25 years or so you lose the neck angle due to soundboard distortion. It's corrected, then it's fine for the next 100 years or so.

Yes, Michael mentions something i forgot to- tucking in braces also minimizes them lifting at the ends with a knock etc.
I leave both my tranny braces about 5mm thick at the ends and about 6mm-7mm wide, so thats a nice square to "inlay" into the kerfing- do it tight and it all locks in sweetly.

My upper bouts are rock solid, my lower bouts are the opposite- best of both worlds.

I've built one uke without tucking the transverse braces under the linings. It was on a redwood top and it was a very early instrument for me. When I strung it up the top cracked at the end of the waist transverse brace, on both sides. Never did that again. I think I made that top a little thin, maybe 0.0700, and like I said, early in my building experience but that uke hangs on the wall as a reminder.
I think Pete is right!!

Well, we seem to have moved on a little from the original question, but to add to the present discussion (about supporting braces).

I've noticed that classical guitar builders often do 2 things that uke makers generally don't do. The first is that they often put supports under the top cross braces (though not the back cross braces). Secondly, irrespective of the back lining/kerfing type, they often use tentellones (individual blocks) for the top, presumably to give it more flexibility.'

Pete Howlett has recently been visiting Les Stansell and was impressed with the sound of his instruments which he commented, 'are made to the same code as his flamenco guitars'. If that's so then maybe he's putting supports under his top braces.

Here's a video of Les making a guitar which clearly illustrates this.

https://www.youtube.com/watch?v=R5AaECtDwWg

Thats a nice video of Les's.
Firstly,
The wants of a classical guitar and a flamenco guitar are very different according to the music repertoire.
Flamenco guitars need a quick attack with immediate decay (NO sustain)-All the sound gets mushy if all those super quick hand techniques are played on a guitar without immediate decay (no sustain).
Classical guitars want good sustain, tone etc for obvious reasons.

Secondly,
the more a top is rigidly anchored at it's the edges (and also the stiffer the sides), the less energy is lost from the top through vibrations being absorbed into wobbly sides. Said again, The stiffer the sides, the more the top can act like a drum head without loss of energy.

A flamenco guitar wants floppy sides and kerfing. (hence they use a cardboard like, energy absorbing wood like cyress to make em.)

Thirdly,
Be wary of attributing a great sound to traditional methods like dovetails, hide glue etc. TO do so is to disregard the decades of thinking that luthier put into fine tuning their building and voicing of tops.
Ie-its like saying the amazing tone of Stradivarius is due to the varnish- i call total and utter BS. (PS- Strad used nails/bolts to help fix his necks on...)

Individual kerfing segments (tentellones) i think are somewhat a sign of the times (of old) and its building methods.

1- Individual pieces are easier to make and fit with the method a traditional classical guitar is built (top down etc).
2- I would not attribute a better or worse sound to tentellones or kerfing or solid linings.

On another note, I line my lower tranny brace up with my upper back brace and join them with a side splint. Don't know if it contributes to anything, but it looks nice.

The traditional Spanish method of making linings is the individual block but really only employed for the soundboard lining. It's a product of how they put the entire instrument together. However Torres did not use this system (apart from the very odd guitar) but he did use continuous kerfed linings. Rarer still is the use of solid linings. Solid linings were used by the odd Spanish maker but it's more associated with N.European making. I can't remember ever seeing soundboard or back transverse braces that were not supported or let into the linings. If it exists it's a very rare thing indeed. Stansell inlets the centre fan brace into the lower block. That's very rare although Panormo was using it in the early part of the 19 th century. I've seen others let the fan braces into the linings but again I certainly would not call that a common practice.
There was a time when the distinction between classical and flamenco guitars did not exist. They were just guitars. Often the Cypress bodied guitars were cheaper because it was a cheap local wood, Braz. Rosewood being considerably more expensive even back then when it was readily available. Eventually Cypress became strongly associated with the flamenco guitar. Things get a little more difficult when you try to pin down the technical differences between the two guitar types. I cannot find a difference other than a slightly lower action on the flamenco. It's often said that the soundboard is made thinner on flamenco guitars to promote the instant response. Pretty much every Torres guitar, including those considered 'classical guitars' have a very thin soundboard. Some go as thin as an astonishing 1 mm but measuring 1.6 mm's on a Torres would hardly come as a surprise. You probably wouldn't confuse a Hauser for a flamenco guitar (they are built much heavier) but a Torres certainly blurs the lines.

Beau, Michael N

Some interesting information here. I for one appreciate that you both give us the benefit of your knowledge and experience.