how to brace when the soundholes are in the upper bout?

[Mark McLean]

A while ago I was in Mandolin Brothers on Staten Island, New York - one of the world's great guitar shops. I admit that I was actually there to buy a banjo , but anyway - on with the story. It was 5 minutes from closing time and I was waiting for a cab to take me (and my very patient wife) back to the ferry. Stan (the proprietor) shows me a Viellette Terz 12-string that he has just got in - like this one.

veillette terz 12 cutaway.jpg (24.19 KiB) Viewed 28674 times

It is not easy to tell the size from the picture but it is a small Terz style guitar - 13.5" wide lower bout, 3-7/8" thickness, 22" scale length, tuned a third higher than a conventional guitar. It was a stunning sounding instrument (a bit mandolin-like) and really fun to play. I only got to play it for a few minutes but I now have a craving to make something similar. I didn't get much of a chance to check out the construction, and now I am starting to muse over how it might be braced. I will email Joe Veillette to see if he will let on. But I also thought I would ask the brains trust what you know about bracing styles when you don't have to work around a central soundhole. Here are a few that I have found while searching the www. I'd appreciate your thoughts
cheers
Mark

top bout holes.jpg (77.25 KiB) Viewed 28674 times

Here's a Mottola guitar - styled like a Tacoma

The dreaded Ovation Adamas

Adamas ovation Bracing.jpg (29.84 KiB) Viewed 28674 times

[DarwinStrings]

One I mucked around with, in hindsight over braced.

uperbouthole.jpg (72.66 KiB) Viewed 28636 times

Jim

[Allen]

There doesn't seem to be anything from stopping you bracing with a standard X if you wanted to use Joes body shape and sound holes pattern. It would certainly be in familiar territory for you before venturing into uncharted waters. It's the smaller body and tuning that really make these style of instruments shine. By far my favourite guitar.

Joes is particularly stylish. I'm looking forward to seeing what you do Mark.

[Mark McLean]

Jim, that certainly is an option that I could manage, and I could lighted it up a fair bit.

You are right Allen - a standard X would be fine for the lower body. I wondered what to do in place of the traditional upper transverse brace since the holes definitely sit in that zone. But more on that in a moment. I also need to explain how the neck block works in Joe's design. He has a heel-less neck that slots into a routed cavity in the neck block, which must be pretty hefty and have an extension under the fingerboard. A bolt incorporated into a strap button on the back goes right through to the neck extension. I have a Baby Taylor which uses the same concept (but less elegant with screws from the front which show in the face of the fingerboard). Kim's memorable F11 "Matey" project was similar. Here is what the Veillette looks like from the back:

Veillette neck joint 2.jpg (6.58 KiB) Viewed 28596 times

So, the neck area must have a pretty strong block, and if I added soundhole reinforcements on each side (like in that Mottola guitar I showed above) the whole upper bout area would be pretty robust - even without a traditional UTB. What do you reckon?

[Clancy]

Mark, Graham McDonald uses a similiar neck joint on his irish bouzoukis.
Here's a pic of mine made using his plans.
The four copper tube lined holes (graham uses brass) are for access to the neck bolts.
The neck block, though large, is made as a frame (think hollowed out) to reduce weight.

Bunya Irish Zouk 3 (Small).JPG (32.39 KiB) Viewed 28582 times

[Clancy]

Found some better pics, but too late to edit last post...

And Graham has a picture of his neck block on his website
http://www.mcdonaldstrings.com/type1.html

Picture 016 (Small).jpg (40.5 KiB) Viewed 28577 times

Picture 014 (Small).jpg (33.59 KiB) Viewed 28577 times

[Mark McLean]

Thanks Craig (and Graham, by proxy) - that is right on the money. I think I can hear the cogs starting to turn in my head. I will also email Graham to buy a copy of his bouzouki book. Love your teardrop instrument BTW.
cheers
m

[Allen]

I'm doing a new tenor uke based around a 2 point mandolin style that incorporates a very hefty neck block made from Spanish Cedar, and neck is glued in a routed pocket. As I don't ever imagine a uke (at least mine) needing any sort of a neck reset, then this will work fine. For a steel string I'd explore the bolt on options such as Graham uses.

Another option is the very stylish =http://kenparkerarchtops.com/Ken Parker method with adjustable neck incorporated into a similar concept.

[Mark McLean]

Well, the Ken Parker design has been filed under "maybe one day".

But (to hijack my own thread for a moment) his website did lead me to this Youtube video of amazing playing by Julian Lage (on a Parker archtop) and Frank Vignola. Check it out if you want to experience a blissful 5:29
http://www.youtube.com/watch?feature=pl ... J7aYeU5V-w

[Kim]

How about a flying buttress..as in Dave White & Rick Turner??

viewtopic.php?t=1370

Cheers

Kim

[Mark McLean]

I have got to admit that I don't understand the purpose of the flying buttress. Is it just to stiffen the sides, or does that have some effect on the geometry and physics of the soundboard too?

[charangohabsburg]

Hi Mark,

The upper bout portion of the soundboard takes more forces than one would imagine. I had to learn this the hard way: click! - I'm referring to this picture:

[...]

On the picture above you also can see that the rosewood part of the soundboard is broken at lower edge of the treble side soundhole. This occurred due to another series of design mistakes.
[...]

The instrument literally started to fold up when tensioning the strings! The upper bout got compressed like a rubber ball.

[jeffhigh]

Ther will always be a compressive force due to the tension of the strings acting between the neck joint and the bridge(fixed bridge)
This is of the order of 180 lbs

This is acting in the plane of the guitar soundboard which must support this load and also the rotational load at the bridge.
If this force is not resisted adequately, the neck and neckblock will rotate towards the bridge.

The problem we face on most instruments is that there is a bloody big hole between these two points so we need to spread the force out so that it goes around the soundhole then back towards the centreline.

On a classical guitar this is done by having fairly large transverse braces above and below the soundhole
)n a Martin style guitar this is dne by UTB on one side and X brace on the other.

On a Guitar without a central soundhole you have the opportunity to allow that compressive force to take it's natural shortest and most effective line directly from neck to bridge though the soundboard, but you do need bracing to avoid the thin plate buckling

Proponents of the flyng buttress believe that you can transfer the load from the top of the neckblock to the bottom of the sides at the waist. There is not often an explanation of how the force gets from there back to the bridge. Personally I am not convinced of the need.

[Dave White]

Proponents of the flyng buttress believe that you can transfer the load from the top of the neckblock to the bottom of the sides at the waist. There is not often an explanation of how the force gets from there back to the bridge. Personally I am not convinced of the need.

Well in my case the main aim of the flying-buttress braces is so that I can brace the upper bout for tone and not structure - there are subtle but very important things that happen there. The tops of my instrument are not in contact at all with the neck or fingerboard and the upper bout is very lightly braced. I'll let engineers draw their force vector diagrams but the rimset top and backs are integral structures and there are plenty of ways for the forces to go back to the bridge. The Larson Brothers used hollow tubes that connected the neck and tail blocks - as does Haans Brentrup, a modern builder. I suspect that similar principles apply.

[jeffhigh]

With the Larson tubes you end up with a proportion of the string load at the bridge being carried in tension though the top to the tailblock, then in compression though the tubes back to the headblock.

I too keep the fretboard off the upper bout, but I do use two small inclined braces glued to the top from headblock to UTB to transfer load out to the sides of the soundhole.

[auscab]

What about a through neck acoustic,assembled like a guitar with a Spanish heel,with the through neck part within the body cut back for space for bracing the top and back ? Built strong enough it will never need a neck re set [ and cant be] , and the whole top gets to move with string vibration,where as normally it slows down above the mid hole design, because of the UTB and the popsicle.

[Mark McLean]

Interesting concepts. I am starting to realize the importance of the appropriate transfer of the forces delivered to the box through the neck block. It is not just a compressive force - also rotational as the entire neck wants to pitch forward and fold the instrument in half. There is an obvious advantage in not having that directed through the upper part of the soundboard. I have seen the dramatic effect that a "Bridge Doctor" has on the tension and shape of the lower soundboard by bracing the rotational force on the bridge against the solid end block. I assume that the buttress does the same thing for the neck block?

Here is a picture from Hans Brentrup's website of the system that Dave referred to.

brentrup carbon tube bracing.jpg (39.62 KiB) Viewed 28408 times

Rob, would this do the job that you were indicating?
What would be the differences between this and the buttress to the sides layout?

Where is a good source for the carbon rods or tubes that would be used for this?
cheers
Mark

[graham mcdonald]

Where is a good source for the carbon rods or tubes that would be used for this?

Archery supply shops. Carbon fiber arrow shafts come in a variety of diameters and wall thicknesses. Alternatively model aeroplane shops. CF rods are used for kites

cheers

graham

[J.F. Custom]

Where is a good source for the carbon rods or tubes that would be used for this?
cheers
Mark

There are many but recently, in Australia, I've been using these guys -

http://www.carbonfiber.com.au

They've got a range of rod and tube, as well as tow etc.

Jeremy.

[auscab]

Rob, would this do the job that you were indicating?

Hi Mark,
I put that suggestion up, but I am a P plater round here with only 1 build under my belt so far,compared to the others that are giving you info as well. so it's a question as well, would it do it ? or why not ?

I think that picture with the Two CF rods looks better than the timber drawing I did , and without the center hole one each side of the blocks looks like it will do it , but what stops the string tension from pivoting the neck at the head block and CF rod point ? apart from the top, there is just two sides and a back. the two sides are basically springs ,and the back would be great if it were straight,but it has a radius in it that I would think would like to straighten out .

So I'm now wondering , could you do a third CF rod in the center bottom from the head to the end block which had a threaded rod in side to give the back more tension? problem is you can see it.

Or could you give the back a Timber center spine to do the job better ,that the two back plates join to, rather than the cross grain strip ?

Or is the normal back set up fine ?

[jeffhigh]

The tension in the back will be around 10-20% of the compressive force on the top (due to the leverage afforded by the depth of the neckblock) so a regular back constuction normally works fine.