A back bracing style for your critique

[Kim]

Well seeing as how a few of you have given me a razz for holding out on you in the "how big is your hole (sound port) " thread, I thought I had best come clean and show some more detail of progress so far on my EIR Adi SJ.

Most of you understand already that I am anything but conventional in my way of thinking. So I hope that you can accept that despite those constant and annoying voices in my head telling me in a wide variety of emotional pleas to "Stick to the plan Kim, just stick to the plan, you can fool around all you like later mate but please, please, just stick to the freakin plan." I have managed to ignore them completely and carry on toward the back of the cave. (Bob and Tim would understand )

Anyhow here is the bracing pattern I have come up with for the back of my guitar.




As you can see, rather than using lateral finger braces extending from the centre of a more robust X in the lower bout, I was more attracted to the idea of maintaining a more robust traditional ladder brace transversing the widest area of the back and then having a very light "X" to help hold the shape of the dome as it extends out to the linings. It is my intention to feather the legs of the X to 0 just just short of the linings, however I have left enough meat on the end of the legs for now to allow for some further procrastination as required. Your collective advice on weather you think I should tuck the x or not are welcome but may not necessarily be followed All of the laterals will of course be tucked.

The joint for the X is a traditional half lap at around 90 degree. The lateral brace acts as a more than adequate joint cap as it has been cut with arrow heads fitting tightly into the lateral sides of the X with little tolerance.



Anyhow, it sustains for a very long time when tapped and despite being glued up for a while, it does not seem to move any more than one would expect with changes in RH.

Cheers

Kim

[Dave White]

Kim,

You know, I am really shocked that you are not sticking to tried and trusted plans that have been developed and proven through generations of builders who of course spent the first half of their careers repairing so that they would know and understand the "force" fully and what not to build

But having said that - "critique" is almost impossible as I don't really know what you are shooting for in all it's glory. The best I can do is comments and observations. I love the structural support of the back's curvature that hybrid X ladder backs give - particularly it gives the front to back arch of the back via the back bracing rather than forcing the back to meet the side profile. I do mine with an X that has its centre close to the waist level and is capped by an upper and lower bout ladder brace. From what you say, your system is giving similar results.

The main reason for the X in the lower bout as I understand it is to give more control on the "tunability" and voicing of the back. So it will come down to how much you can voice the back via this bracing pattern and what voicing you want to do. For me and my "personal" style of building, I would have the lower ladder brace much lower and tapering more in profile out to the bout edges , and I'd probably taper the top two ladder braces as well but keep them at the height you have them. The principle to me is the same as the top - stiffer in the middle but less stiffness needed at the edges to make the back responsive. But then this is why I have the X join at the waist, as I don't want it smack dab in the middle of the most responsive part of the back. But then again, if you are going for the back as a pure reflector then your bracing is probably as you would want it.

As for the X brace ends, I would taper them down but set them in lining pockets. Responsiveness of the back here doesn't look like an issue - particularly if you keep the big meaty lower bout ladder brace as is - and I would be happier with the protection against them popping loose if they are just there to keep the dome.

It's all horses for courses and it sounds as though this bracing is doing what you want it to.

Interesting stuff though!!

[Bob Connor]

I'd be tucking those x-braces into the linings Kim. A tap to the back can easily dislodge them. They're not that hefty after all.

If you're hell bent on heading toward the back of the cave I'd use it as is, observe and listen once you've got it built and see if it achieves the effect that you want.

Of course by not sticking to the plan you won't have anything to compare with.

You'll know whether it has the flexibility you want if it rumbles your gut when you play it.

It's progressing nicely mate.

Bob

[Hesh1956]

Very nice work Kim!!!!

If you have not noticed many of us feel somewhat differently about how a back works - or should work.

There is the camp that wants stiff, reflective backs and there is the camp that sees the back as both a resonator AND a pump. I am in the second camp.

Folks in the second camp want a back to pump or move as well as reflect and resonate. This means that the bracing of the back needs to permit some movement. This is also why as Dave explained very well bracing need not be as substantial near the edges of a guitar.

I think that what you have here will work very well and I see it as a hybrid of both camps. The X pattern stiffens the center but permits movement around the edges. The major structural member across the center of the sweet spot of the back will stiffen things up.

Regarding tucking the brace ends into the linings I agree with Bob. I have studied 1930's era Gibsons and where ever they did not tuck a brace it came loose. They also would taper some brace ends to nearly nothing, just a few thousandths, and then just glue the top over them with out inletting them into the kerfed linings but mashing them between the back and kerfed linings. This is something that you might consider too for the smaller brace ends.

Great work bro!

[Dennis Leahy]

...Of course by not sticking to the plan you won't have anything to compare with.

Kim, is it too much of an inside joke if I chuckle at that?

There is a saying in the US that you can tell who the pioneers were - they're the ones with arrows sticking in their backs.

I am probably the last person you need advice from, especially if you're looking for the "voice of reason" to tame that desire to experiment - and on your first build, no less!

Your work looks excellent from where I'm sitting.

Dennis

[Dominic]

Hey Kim,
(and with absolutely no offence intended to anyone unless you think you deserve it)
if we had all stuck to the plan we would never have thought to go past banging sticks on the ground to make music, or Torres would never have started using fan bracing, or Martin would ... you get the picture.
How does the saying go, "plans are made to be broken" or something like that.
Dom

[Craig]

G'day Kim,

That's some beautiful work there mate. Tuck the braces and go for it.

Looks to me to be a compromise between a reflecting back and a chest thumping back. Difficult to determine with out 'being there'.

Great work Kim.


Cheers, Craig

[Kim Strode]

Hello Kim,

Thanks for sharing your work with us Kim, particularly your ideas on bracing. Also, thanks to everyone else for their feedback on your bracing design, it has been very informing.

I am very interested in alternative bracing techniques, particularly with classical guitars, and don't see why advances in one style of guitar, cannot cross over.

I am only a novice compared with the vast majority of the forum members, so I've been checking in to the forum on a daily basis for input. It's a great sharing environment.

Thanks, Kim

[Kim]

It's a rough photo but it shows what happened to my back bracing once I took some of you input on-board, I will as advised be tucking the X ends at around .090".





It will be interesting

Man I neeeed another camera, most mobiles have more pixels than the piece of crap I have now...maybe if I give up buying wood for a while....naaaah that's a stupid idea, next I will be saying I'll give up beer


Cheers

Kim

[Paul B]

next I will be saying I'll give up beer

Kim, NEVER EVER SAY THAT! Just don't go there.

[Bob Connor]

Looks like it'll be a bollock rumbler to me.

What note does it ring at when you tap it?

You should be able to get two clear notes out of it - a higher pitched ping and a lower bottom end rumble.

I don't check this myself but I intend to. I'm just thinking about Al Carruth's theory of tuning the back to a different note to the top.

It may be of use for future reference seeing as though you're stepping outside the square (or further to the back of the cave) on this one.

Paul - if he gives up beer I'll bare me bum on the Geelong Post Office steps on any given Friday he cares to nominate.

Bob

[Craig]

Looks like it'll be a bollock rumbler to me.



Bob

.......Bob has a way with words.....


It looks SUPER good to me Kim.

The back on my No.1 Mahogany guitar has a pitch one whole note lower than the top, and it kicks arse.

Gets rid of any wind build up in the gut each time I play it !

I think the important thing is to not have both plates the same pitch ,to avoid 'wolf notes ' and the like. Alan Carruth recommends having the back a higher pitch than the soundboard to avoid it's pitch meeting up with the back's pitch , after the soundboard settles and lowers it's own pitch. That didn't come out right , but I hope you understand.

This is going to be a great guitar buddy ! Fantastic workmanship as usual !


Cheers , Craig