Official Luthiers Forum! :: View topic - To Hesh: Follow up on use of Balsa for composite top

It's really interesting how composite top develops?

I just want to give a heads up on a potential problem:
Balsa is very weak in shear along the grain, when it's used as a core material (and it's used a lot) it is used as end grain core, that is perpendicular to the orientation you've used it.
I don't know that you'll actually have a problem or not, it's just not the conventional orientation for a balsa cored structure.
Anyway, if you used end grain core, you'd have a much stronger top and no additional weight.

_________________

I've also seen balsa cores with multiple holes drilled in the balsa- lots of variations possible!

I have seen drilled out cores, but not with Balsa.Since Balsa is so light weight anyways, I wonder how much of a difference it would make in the final weight (probably not more than 2 or 3 grams. Is it then worth the trouble with the associated loss of stiffness?) Lots of interesting questions arise!

In a prior post, you mentioned about 10% - 15% weight reduction in a 115g top. That's 11 to 16g. 2 to 3 grams of that is 20 to 30% of that number. If you're chasing that last 1%....

I don't mean to stir the pot too much as this kind of thing is pretty interesting but, I wonder how much of a difference in tone or power a balsa core would have over a solid top?

p.s. There should be very little loss of stiffness from drilling holes in the balsa core.

Author:	patmguitars [ Mon Mar 29, 2010 12:33 pm ]
Post subject:	To Hesh: Follow up on use of Balsa for composite top
Hi Hesh Here is a picture of the combination of Balsa and Cedar that I use for the middle layer of my composite tops. The other picture shows you the edge of a complete top. The top Cedar layer is 1mm thick (it tapers to 0.6mm in the periphery of the lower bout), the middle layer of Balsa and Cedar is 0.5mm and the bottom layer of Spruce is 0.5mm. I use System Three Structural Epoxy to hold it together. Cheers Pat

Author:	Hesh [ Mon Mar 29, 2010 4:51 pm ]
Post subject:	Re: To Hesh: Follow up on use of Balsa for composite top
Thanks Pat!!! The two questions that I would have had you answered for me in advance - thanks for that too! Very nicely done!

Author:	senunkan [ Mon Mar 29, 2010 11:46 pm ]
Post subject:	Re: To Hesh: Follow up on use of Balsa for composite top
Hi Pat, How heavy is the top? Wouldn't the epoxy add lot of weight to the top? Unlike the typical nomex top, which the gluing area is limited and thus the amount of epoxy used will be limited, this composites balsa top looks like the whole top area is being glued. Or do you route pockets of air space in the balsa layer, like internal struts kind of thing? Please correct me if I assumed wrongly. Thanks. Sen

Author:	patmguitars [ Tue Mar 30, 2010 8:14 am ]
Post subject:	Re: To Hesh: Follow up on use of Balsa for composite top
Hi Sen The surfaces are in full contact, which means that there is more epoxy required than with nomex. Still, the weight of the unbraced top is about the same as a regular Cedar top, +/- 115 gr. It can however be made thinner and with lighter bracing, so once braced and thicknessed is is about 10-15% lighter than a regular top. Cheers Pat

Author:	senunkan [ Tue Mar 30, 2010 10:51 pm ]
Post subject:	Re: To Hesh: Follow up on use of Balsa for composite top
Thanks! It's really interesting how composite top develops? Compare to the nomex composite top, it would be interesting to see how the sound would turn out to be. My guess is that since it's a solid top it would not sound "hollow" like the nomex composite top.

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Author:	JohnAbercrombie [ Tue Mar 30, 2010 11:38 pm ]
Post subject:	Re: To Hesh: Follow up on use of Balsa for composite top
senunkan wrote: It's really interesting how composite top develops? I've also seen balsa cores with multiple holes drilled in the balsa- lots of variations possible! Cheers John

Author:	Jim Watts [ Wed Mar 31, 2010 12:15 am ]
Post subject:	Re: To Hesh: Follow up on use of Balsa for composite top
I just want to give a heads up on a potential problem: Balsa is very weak in shear along the grain, when it's used as a core material (and it's used a lot) it is used as end grain core, that is perpendicular to the orientation you've used it. I don't know that you'll actually have a problem or not, it's just not the conventional orientation for a balsa cored structure. Anyway, if you used end grain core, you'd have a much stronger top and no additional weight.

Author:	JohnAbercrombie [ Wed Mar 31, 2010 1:03 am ]
Post subject:	Re: To Hesh: Follow up on use of Balsa for composite top
Jim- Thanks for that 'heads-up' on grain direction. I know from boatbuilding that balsa core is end-grain, but do the guitar-makers who use balsa use it in that orientation? I've only seen one guitar balsa core close-up and wasn't paying 110% attention- it certainly didn't have the 'bunch of squares' look of boatbuilding end-core. I was wondering about the glue absorption rate into end-grain core. In boatbuilding you want good resin penetration into the core, but with the emphasis on low weight for guitar tops, can this (glue/epoxy absorption) be a problem? John

Author:	patmguitars [ Wed Mar 31, 2010 6:23 am ]
Post subject:	Re: To Hesh: Follow up on use of Balsa for composite top
Jim said: Quote: I just want to give a heads up on a potential problem: Balsa is very weak in shear along the grain, when it's used as a core material (and it's used a lot) it is used as end grain core, that is perpendicular to the orientation you've used it. I don't know that you'll actually have a problem or not, it's just not the conventional orientation for a balsa cored structure. Anyway, if you used end grain core, you'd have a much stronger top and no additional weight. _________________ Thanks for the info Jim. So far (5 composite top guitars), no problems with it. As you may have noticed on the picture, the most sensitive area of the top (bridge area and towards the soundhole) is made of Cedar in order to have a stronger core in that area. I am not sure if I can find pieces of Balsa large enough to use the endgrain for my purpose. The use of many smaller pieces put together would require more epoxy, which would make the top heavier and negate a lot of the effect of the composite top. If I can ever dig a large piece of Balsa though, I will give it a try. John said: Quote: I've also seen balsa cores with multiple holes drilled in the balsa- lots of variations possible! I have seen drilled out cores, but not with Balsa.Since Balsa is so light weight anyways, I wonder how much of a difference it would make in the final weight (probably not more than 2 or 3 grams. Is it then worth the trouble with the associated loss of stiffness?) Lots of interesting questions arise! Cheers Pat

Author:	Andy Birko [ Wed Mar 31, 2010 8:13 am ]
Post subject:	Re: To Hesh: Follow up on use of Balsa for composite top
patmguitars wrote: I have seen drilled out cores, but not with Balsa.Since Balsa is so light weight anyways, I wonder how much of a difference it would make in the final weight (probably not more than 2 or 3 grams. Is it then worth the trouble with the associated loss of stiffness?) Lots of interesting questions arise! In a prior post, you mentioned about 10% - 15% weight reduction in a 115g top. That's 11 to 16g. 2 to 3 grams of that is 20 to 30% of that number. If you're chasing that last 1%.... I don't mean to stir the pot too much as this kind of thing is pretty interesting but, I wonder how much of a difference in tone or power a balsa core would have over a solid top? p.s. There should be very little loss of stiffness from drilling holes in the balsa core.

Author:	patmguitars [ Wed Mar 31, 2010 10:10 am ]
Post subject:	Re: To Hesh: Follow up on use of Balsa for composite top
Andy said: Quote: In a prior post, you mentioned about 10% - 15% weight reduction in a 115g top. That's 11 to 16g. 2 to 3 grams of that is 20 to 30% of that number. If you're chasing that last 1%.... I don't mean to stir the pot too much as this kind of thing is pretty interesting but, I wonder how much of a difference in tone or power a balsa core would have over a solid top? p.s. There should be very little loss of stiffness from drilling holes in the balsa core. I am not sure 2 to 3 grams are going to make a noticeable difference. The main challenge with this design is the amount of epoxy. I have managed to bring it down by about 1/3 since I started, mainly by switching to T-88 and by getting a better understanding of how much is enough. Stir away that pot!!! We need the discussion! To answer that question, my findings are very similar to what other luthiers who use composite tops are saying. I didn't invent any of the elements of my design, but merely put together a melting pot of what I have learned from articles on the subject by Randy Reynolds, Fritz Mueller, Kenny Hill, Robert Ruck and Gernot Wagner. There are many articles and comments by luthiers and players alike on the sound produced by a composite top instrument. Having said that, my main source of motivation comes from the comments I have had from clients and players who have tried my version, and they almost all agree (so far about 15 for and one against) that they prefer the composite top over the traditional one. That alone is plenty of reason to continue working in that direction. Cheers Pat

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