Bending Balsa...it's a wrap
Just a summary of results if you're going to attempt tight bends like this ring:
1. It's going to be very difficult bending it parallel to the grain (the long way) like I was. So use A-grade flexible competition balsa.
2. Soak the wood in an ammonia solution like Windex. (I soaked it for a half hour but that was probably overkill). This will break down the lignin structure and soften the balsa on the molecular level (don't worry, once the ammonia evaporates the wood will reharden and be pretty much "locked" in its new shape.
3. Soaking in hot water for several hours didn't work for me. The ammonia definitely did.
4. Wrap the balsa around the
outside of the form. Trying to cram it into the inside of the form will only result in major and fatal cracking, crimping and splintering.
5. Usa flexible self-adhesive Ace bandages wound around the outside in spiral-fashion to hold it in place -- much better than closthespins. It holds tighter without leaving dent marks. Start wrapping from the
middle and work your way to the ends of the balsa strip, which are the most resistant to bending.
6. Join the ends with a lap joint. It's much stronger than a butt joint. Bevel the overlap area so it'll lay flatter once joined (see pic).
The join may bow outward slightly leaving a "bump" in the ring. Even with sanding I haven't been able to get rid of it completely, just minimize it.
Postscript: Thanks to
Incongruent,
Rex R,
dr wogz, James Duffy, and Micromeisterfor the feedback on using plywood instead of balsa. Due to time constraints I finally picked up some 1/64" birch ply and it was a breeze to form the ring and glue the ends together with a lap joint. Took all of 10 minutes.
The weight penalty is negligible. Neither balsa nor ply registered on my postage scale, meaning both weighed less than 1/10 oz, though the ply "feels" a hair heavier. I'm not building a competition model so anything less than 1/10 oz difference makes no difference to me. If it's critical to what you're building, go with balsa; it's more of a struggle in my experience but hopefully what I've discovered will cut your fabrication time drastically and help you avoid the pitfalls I didn't.
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