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Min top thickness with lattice bracing on a SS guitar?
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=50434		 Page 1 of 1
Author:  Colin North [ Tue Mar 20, 2018 4:04 am ]
Post subject:  Min top thickness with lattice bracing on a SS guitar?
Anyone using lattice braced tops on SS guitars?
How thin can you safely go with soundboard thickness, what sort of range?
Is there any minimum thickness you should probably not go less than?
Author:  bluescreek [ Tue Mar 20, 2018 6:38 am ]
Post subject:  Re: Weight saving with lattice bracing on a SS guitar
you need to show that pattern you are planning to use. Of the 2 lattice braced guitars I saw , I wasn't impressed in the sound quality ' It is more than weight control it is where the top is allowed to move and how if can move.
Author:  Trevor Gore [ Tue Mar 20, 2018 7:10 am ]
Post subject:  Re: Weight saving with lattice bracing on a SS guitar
Colin North wrote:
Anyone using lattice braced tops on SS guitars?
How thin can you safely go with soundboard thickness, what sort of range?
Is there any minimum thickness you should probably not go less than?

Yes. Those are broad questions, though, Colin. Sparse lattice? Dense lattice? With or without CF? What wood for the top?

Here's one I wrote about on the forum a while back.

If you use a sparse lattice in just wood and a spruce top, it's much like a double X type of pattern and you can use typical X-brace type dimensions.
Author:  Colin North [ Tue Mar 20, 2018 11:08 am ]
Post subject:  Re: Weight saving with lattice bracing on a SS guitar
OK, sorry for the lack of details.
Thinking of a triple X-braced top, 25' radius - no CF. More of a sparse lattice.
Basically a "normally" X brace, but forward shifted.
Plus 2 further intersecting X braces where the "tone bars" would normally be.
Sitka soundboard and bracing, upper/medium density (~0.45 S.G)
I am planning on putting a "doubling" spruce plate between soundhole braces to help support the upper bout area.
Lower bout is 16-1/16" wide, upper is 12-1/16", body length 20".
Perhaps the original weight saving part of the title was misleading (edited), more looking to thin the soundboard as much as practical.
I'm looking to shift the balance from my past models which have been quite a thick top, lightly braced, to the other way round.
Soundboard as thin/light as practical. with tall bracing.
Lower X's could be perhaps a high as the main X braces.
P.S. Got to say it again, Stunning Guitar Trevor.
Author:  Trevor Gore [ Tue Mar 20, 2018 5:36 pm ]
Post subject:  Re: Min top thickness with lattice bracing on a SS guitar?
Colin North wrote:
P.S. Got to say it again, Stunning Guitar Trevor.

Thanks, Colin.

I think that when you're about to try something quite different from your normal fare it's very hard to avoid doing "proper" design work. Perhaps time to dive into the book...

As a start point, try setting a top thickness of 2.00mm for "average" spruce and back it out from there. The design methods are mostly covered in Section 4.4 (braces) and Section 4.5 (panels). Only about 35 pages... ;)
Author:  Colin North [ Tue Mar 20, 2018 5:44 pm ]
Post subject:  Re: Min top thickness with lattice bracing on a SS guitar?
No worries, bedtime reading.... ;)
Author:  IanC [ Thu Mar 22, 2018 6:21 am ]
Post subject:  Re: Min top thickness with lattice bracing on a SS guitar?
A few years ago I had a long chat about lattice bracing with a local maker of high end classical guitars and decided to try a lattice steel string. My basic philosophy was to use more smaller braces on a lighter top and aim overall for a very light instrument. There's a bracing sketch attached. I used a 2mm spruce front, B&S are English cherry. The weirdness in the cutaway area is because I also took the opportunity to have a first attempt at a scoop cutaway. The braced front weighed 210gm, the whole guitar felt pretty light at 1.59Kg (3.5lb). The guitar is extraordinarily bright - scary someone said - with a very sharp attack. The Tele neck pickup of acoustics, the complete opposite of a Dread. Very responsive and seems loud in normal domestic circumstances but take it into a pub full of squeezeboxes and fiddlers and you'll wish you had something heavier. I very much didn't make it to sell but as it happens my son in law, who mostly plays electric, liked it so it gets used and I can keep an eye on it.

Over time the front bellied more than I'd like but one effect of the lattice is to keep the bellying perfectly smooth. There's no distortion or sign of stress points, I don't feel anything is about to crack. However the action has needed adjusting a couple of times and I worry about it's long term stability. I've never seen the point of adjustable necks - if I wanted to persevere with this design this might be the exception. But before that I'd use a deeper X brace, this one was only 11mm, I'd normally use more like 14

I think it was interesting to make a guitar with the tone so far removed from "normal". However I think there's a problem with the basic idea of more but lighter braces and that lies in the fact that the depth of a brace is way more effective than the width. Suppose I use twice as many braces of half the dimensions, ie. to keep the same weight of bracing. Half the actual height does much more than halve the strength of the brace. But if I use twice as many braces of half the strength the height is only reduced by a fraction and the overall weight of the bracing goes up. Now it may be that you can use a thinner top to compensate - I reckon the unbraced top is somewhere between 2/3 and 3/4 of the weight of the finished top - but, as ever, it's complicated and experimenting can sometimes show where the conventional designs have got it about right!
Author:  phil [ Thu Mar 22, 2018 8:24 am ]
Post subject:  Re: Min top thickness with lattice bracing on a SS guitar?
Ian,

I think your response demonstrates the enormous value of the OLF. In going to all that work (gosh, it looks like a lot of work) and sharing your findings, I think you may have just saved Colin from his own pile of work . . . or at least given him some very good grist for the mill before he tackles his own variation on the theme.

Thanks for sharing so generously.
Author:  IanC [ Thu Mar 22, 2018 8:42 am ]
Post subject:  Re: Min top thickness with lattice bracing on a SS guitar?
phil wrote:
Ian,

I think your response demonstrates the enormous value of the OLF. In going to all that work (gosh, it looks like a lot of work) and sharing your findings, I think you may have just saved Colin from his own pile of work . . . or at least given him some very good grist for the mill before he tackles his own variation on the theme.

Thanks for sharing so generously.


Couldn't agree more about the value of the forum. I mostly lurk, occasionally ask a question. If this time I can put something back I'm honoured. And I look forward to seeing what Colin produces.
Author:  Colin North [ Thu Mar 22, 2018 9:05 am ]
Post subject:  Re: Min top thickness with lattice bracing on a SS guitar?
Mr Chisolm, you are a gentleman and a scholar.
Thank you for taking the time to reply to my question, and in so much detail.
Nice looking guitar, looks like it may be a Small Jumbo?
I understand the point you were making about the low lattice braces, and also agree that 11mm is a bit on the low side wow7-eyes for the X's.
Did you get and MoE long for the spruce? Or even an SG? What were your impressions about the stiffness?
Cherry, I'd like to try some lovely wood, got a picture?
Sorry for the 20 questions...
I'm using Myrtle for this particular guitar, sides already bend (very easily)
BTW, I like your website, very well put together, and I will keep you updated.
Author:  Mike Mahar [ Thu Mar 22, 2018 10:01 am ]
Post subject:  Re: Min top thickness with lattice bracing on a SS guitar?
There are two different objectives when bracing a classical vs a steel string guitar. You want to maximize the brightness of the classical because the nylon or gut strings are very weak in the high overtones. The steel string, on the other hand, has more brightness than you really want. It's more difficult to get an even bass. The bracing patterns have been developed to reflect these two different goals.
The lattice brace is successful for classical guitars. Most likely this is because it produces bright guitars. Converting this design to the steel string should require some careful thought. I have no idea how I would modify a lattice to reduce brightness and emphasize bass.
As for making the top thinner, I suspect that a thin top also promotes brightness. Taken to an extreme, a banjo head is a very, very thin top. There's not much bass there. Granted, a banjo head is quite a different beast from a guitar top so the extrapolation may be completely bogus but I suspect that the thinness of the head contributes a lot to the bright sound of the banjo.
Author:  Colin North [ Thu Mar 22, 2018 11:33 am ]
Post subject:  Re: Min top thickness with lattice bracing on a SS guitar?
Mike Mahar wrote:
There are two different objectives when bracing a classical vs a steel string guitar. You want to maximize the brightness of the classical because the nylon or gut strings are very weak in the high overtones. The steel string, on the other hand, has more brightness than you really want. It's more difficult to get an even bass. ............................................. Taken to an extreme, a banjo head is a very, very thin top. There's not much bass there. Granted, a banjo head is quite a different beast from a guitar top so the extrapolation may be completely bogus but I suspect that the thinness of the head contributes a lot to the bright sound of the banjo.

I see your point.
But also I seem to remember that an overly thin soundboard can lack brightness (been there, got the T shirt), it moves the response towards the bass, I'm just looking to restore that brightness with stiffer bracing.
I have used double X bracing for a guitar reasonably successfully to restore overall stiffness where the top was over-thinned (blood from a cut finger everywhere) and it sounded fine.
Ervin Somogyi and his apprentices/followers seem to build with thinner tops and stiffer braces, looking to get more volume from a soundboard that is typically lighter overall than "traditional" builds, and their guitars don't sound too shabby, although I know they are not to everyone's taste - what is? laughing6-hehe
Not sure about your banjo comparison either.... :? Different kettle of fish.
Author:  IanC [ Thu Mar 22, 2018 6:33 pm ]
Post subject:  Re: Min top thickness with lattice bracing on a SS guitar?
Colin North wrote:
Mr Chisolm, you are a gentleman and a scholar.
Did you get and MoE long for the spruce? Or even an SG? What were your impressions about the stiffness?
Cherry, I'd like to try some lovely wood, got a picture?
...
BTW, I like your website, very well put together, and I will keep you updated.


You're going to have to enlighten me as to MoE and SG. It was a pretty ordinary bit of spruce, grain not particularly even or narrow. My recollection is that it was stiffer than average. Since I knew I was going to work it thinner than I usually do I did make sure there was negligible runout.

I love that cherry. I started off about 20 years ago with a couple of trunks, this guitar used some offcuts - it's got a 4 piece back, sorry, no pictures. Picture attached of a nice back from the same tree. There's something about starting with the bark still on! btw., last time I was in Dave Dyke's emporium - luthierssupplies.co.uk, I assume you know him - he had some very similar English cherry at a very fair price.

Mike Mahar wrote:
There are two different objectives when bracing a classical vs a steel string guitar. You want to maximize the brightness of the classical because the nylon or gut strings are very weak in the high overtones. The steel string, on the other hand, has more brightness than you really want. It's more difficult to get an even bass.


Agree totally - this is something I've learnt (from reading Ervin Somogyi's book) since making this guitar. In fact I should have known it all along beacause the very first guitar I made, around 1970, was a large steel strung instrument, fan braced because that was the only plan I could find in the days before the Sloane books. It was loud and bright and impressive compared with the plywood junk my student friends were playing but had no bass at all. This guitar - X braced lattice - is very different, particularly in that the bass strings are very responsive, they just have a very bright timbre. I don't think I'll be pursuing this particular direction any further but in terms of being able to control the tone of my instruments I feel I learned something useful.
Author:  Colin North [ Fri Mar 23, 2018 4:32 am ]
Post subject:  Re: Min top thickness with lattice bracing on a SS guitar?
Sorry about the shorthand!
MoE - Modulus of Elasticity, just a measure of stiffness. Can be obtained by deflection testing. (weight on a plate as is known collocquially)
SG - Specific Gravity or relative density, water being 1.0
That cherry is really, really nice.
Author:  IanC [ Fri Mar 23, 2018 11:29 am ]
Post subject:  Re: Min top thickness with lattice bracing on a SS guitar?
Colin North wrote:
MoE - Modulus of Elasticity, just a measure of stiffness. Can be obtained by deflection testing. (weight on a plate as is known collocquially)
SG - Specific Gravity or relative density, water being 1.0


You put me to shame there. I actually have an engineering background but somehow that career and my instrument making fit in different boxes. I have a major workshop rebuild coming up, might be time to get a bit more serious about the physics.
Author:  Colin North [ Fri Mar 23, 2018 11:52 am ]
Post subject:  Re: Min top thickness with lattice bracing on a SS guitar?
Have you read Trevor Gore's book? I can recommend it.
Not cheap, but you won't regret it.
http://www.goreguitars.com.au/main/page_the_book_overview.html
Author:  Alan Carruth [ Sun Apr 01, 2018 3:05 pm ]
Post subject:  Re: Min top thickness with lattice bracing on a SS guitar?
You can apportion the load between the braces and the plate. Arch top guitars take almost all of the load on the top, with the braces mostly making up for the stiffness lost when you cut the hoes. On a 'normal' flat top the top plate itself takes part of the load, and the bracing takes the rest. As you add braces, at the limit the lattice takes all of the load, while the top is just a membrane filling in the spaces between braces to move air.

A lot of the 'bass balance' of the sound comes simply from box size: bigger box, more bass.

A wide/long top exacts a structural penalty: you have to beef it up to maintain sufficient stiffness, and the mass goes up faster than the area. Power output seems to be pretty much a function of the ratio of A/m. Where the power input is more limited, as on a Classical, they tend to stick with smaller boxes, and that also helps the balance of treble to bass. Steel strings tend to carry more tension, so you can get away with the bigger top.

Also, the A/m ratio is, in part, determined by the structural efficiency of the brace system. Early 'ladder' braced gut strung guitars were small, and stayed about the same size for a couple of hundred years. When 'fan' bracing came in, around 1775, iirc, guitars started to get bigger. X-bracing is even more structurally efficient than fan bracing, so you can make the top bigger and still keep the mass down, all else equal.
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