I've never used balsa as a core material, however I'm very familiar with balsa from other hobbies.  I'm thinking it may be my best bet as a core that needs to be shaped. I know I'll have to drill it.  What else do I need to know that is different from a cloth or honeycomb based core?

Hi drum, 

Depends what you mean by needing to be shaped. Do you mean being able to form a sheet over a curve, or sand/grind it to form an unusual shape? I've only used it from half inch upwards, and not sure if it comes much thinner, but as the king said, it normally comes in sheets of end grain blocks glued together with a scrim on one side. So the sheet will bend one way, but not the other, and when it does bend you're left with loads of gaps between the blocks that will need to be filled with thickened epoxy.

If stresses on your part will be high, balsa is a good option. Or also PVC  foam or honeycomb.

Polyurethane Foam is a completely different material to polystyrene Foam, Any resins or solvents will normally attack polystyrene and melt it, Polyurethane and balsa are widely used in the marine industry for core applications. From racing dinghys to super yachts.........

Thanks for the advise.  So the thin sheets from the hobby shop that are normally used on RC airplanes wont work?  The shape I'm making is pretty flat.  Just has a thin airfoil shape.  I was also looking at foam, but figured balsa would be stronger, even though the part won't receive much stress.

You can use flat balsa as it comes from a hobby shop, it is just not the typical way with composites.




When people refer to balsa core it usually refers to the type (end grain balsa) that is supplied as small blocks held together with a scrim layer on one side. This way you get the advantage of the end grain strength in the sandwich.




Personally I avoid using balsa, being a natural material it can absorb moisture before you have even used it, and then that moisture will inhibit the cure of the resins bonding to it. If the bonds are not good then you can serious problems down the track. Foams are much lighter, more predictable and safer in the long run.

I have very successfully used Balsa cores for making a number of riflestocks.  I have used 1,5 to 2 cm thick Balsa "boards" laminated together with layers of Unidir CF to form a very stiff "core".

I shaped the core to the final form of the stock, then sealed the entire stock with laminating epoxy, left to cure fully, sanded down and built up a couple of 200gsm and 160 gsm CF on the outside, using wet-lay.

This was my very first CF projects, nearly 12 years ago, both the first stocks have been extensively used, while hunting in adverse conditions (New Zealand mountains, hunting Thar and Chamois ) and target shooting.

They are holding up very nicely ... No distortions or damage, nor have they changed weight (No lasting moisture absorption)   One prototype balsa/CF "raw" stock is holding up a ceiling beam, going on 10 years now, with no visible distortion.. loosely calculated it holds more than 800 kgs of force. It consists of three layers of 2 cm thick balsa boards, laminated with four layers of Unidir CF.

I recommend Balsa/CF composites very highly ...

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I know this is a very old thread, but may I ask what criteria you used to select laminating epoxy to seal the stock? And, would you use the same epoxy today? Are there any newer materials that might perform differently than laminating epoxy as a sealer?


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