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Old 02-03-2007, 06:04 PM   #1
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Default What's the best way to bend balsa?

What is the best technique you know for bending (shaping) balsa skins around complex curves?

We all know that it takes 24hrs to saturate 1/32 balsa sheeting. Three times as long for 3/32. After saturated you could tie it in a knot.

Is there a quicker method to make balsa pliable?
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Old 02-03-2007, 10:29 PM   #2
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Default Looking For Curves?

Hello Res59, I've never soaked balsa for much more than an hour, and often get impatient and try it sooner! I use scalding hot water and hold the piece submerged by placing a metal knife or heavy utensil on it.
As I'm rubber-banding it in place (no glue, yet) I place scrap balsa strips between the piece and the rubber bands, to prevent the rubber tension from leaving "furrows" in the soft wood. Once it's in place and being held (nearly) into the contours I want, a heavy misting of more water on the outside seems to help.
After an overnight drying, I remove the rubber bands and glue in place. It takes a bit of trimming, and occasionally will develop a crack. Most times it works out just fine.
The thickest wood I've used with this method is 1/16" "A" grain balsa. It's worked on some fairly tight and complex curves.
I've also heard of modelers using ammonia to break down the fibers more, but never had to resort to that.
Ron
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Old 02-04-2007, 02:05 AM   #3
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Thanks Ron,

Thats pretty much the same methods I've used. The area I'm covering now has to be done with 3/32 sheeting. And is a rather large area. Initially I glued the strips into larger sections (as suggested by the mfg of the kit) but that didn't work out. However I was able to get the section I needed using narrower strips (3") then edge gluing them in place after forming. I still have the mirror side to do yet then I'll be posting pics in a couple of days.

Here's the thread:
http://www.wattflyer.com/forums/showthread.php?t=13228

Ray
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Old 02-04-2007, 02:29 AM   #4
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Made a P 40 fuse, 24 in. long of pink foam, covered with 1/16 balsa. Cut it a little oversize, soaked it in the tub in warm water for about 1/2 hr. laid in on the carved fuse and wrapped it with horse leg bandages. dried overnight and peeled off like an eggshell. Carved one side to fit the foam closer and glued to the foam with aliphatic carpenters glue with a sawtooth pattern and wrapped loosely with the bandages. When that dried carved the other piece to fit close to the first piece for a tight seam and repeat glueing that piece. Covered with Micafilm for a smooth, light finish.

Gord.
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Old 02-04-2007, 03:17 AM   #5
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Default One BIG Corsair!

Hi Ray, guess I missed your main thread somehow, boy, that's a great-looking build! You've got a real project on your hands, sounds like you have the experience to do it.
Your idea about cutting the sheet into strips is a good one; It there's a compound curve that's sometimes the only way to work the wood. It bends so nice across the grain, but along the grain....
Do you tape the edges as you glue them? I saw where you advised doing this on sheet-joints, but on the edges of a compound I sometimes have trouble getting them to mate, it's not a straight line.
Good Luck, I'll be checking in on the main thread from now on!
Ron
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Old 02-04-2007, 05:02 AM   #6
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using amonia does work for bending/forming balsa but does weaken it a bit permanently.....i have never soaked balsa because it takes too long to make it pliable then you have to leave it dry for a day or 3 before it can be glued....the quickest way ive found to form balsa is to steam it in the oven for 2 hrs. you lay the balsa (up to 3/16th inch thick) on the rack in an oven....in the bottom rack you put in a pan of water...have the oven & water preheated to about 200 deg before you put the balsa in there....works real good & dont have to wait a day or more for the wood to dry......usually it dries in about 6 to 8 hrs....

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Old 02-04-2007, 07:58 AM   #7
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Originally Posted by Sky Sharkster View Post
Hi Ray, guess I missed your main thread somehow, boy, that's a great-looking build! You've got a real project on your hands, sounds like you have the experience to do it.
Your idea about cutting the sheet into strips is a good one; It there's a compound curve that's sometimes the only way to work the wood. It bends so nice across the grain, but along the grain....
Do you tape the edges as you glue them? I saw where you advised doing this on sheet-joints, but on the edges of a compound I sometimes have trouble getting them to mate, it's not a straight line.
Good Luck, I'll be checking in on the main thread from now on!
Ron
Not needed if they formed correctly. I use a gel CA to put it on the frame then a thin CA on the edges. A little harder to sand but with patience it comes out nice. (Using the heavy gel you can glue it the framework while the wood is still wet, as soon as its dry enough to absorb the thin CA wick a little into the joint and everything will dry in place.) Srinkage will be very small due to only the surface being wet.

Another point is that if you are doing a wing (glueing wet wood) this could cause a twist to form. Make sure you have the frame held tight to your build board with the proper dihedral and washout. I have extra pieces of wood screwed to both the table and wing.

Originally Posted by freecrashlessons View Post
using amonia does work for bending/forming balsa but does weaken it a bit permanently.....i have never soaked balsa because it takes too long to make it pliable then you have to leave it dry for a day or 3 before it can be glued....the quickest way ive found to form balsa is to steam it in the oven for 2 hrs. you lay the balsa (up to 3/16th inch thick) on the rack in an oven....in the bottom rack you put in a pan of water...have the oven & water preheated to about 200 deg before you put the balsa in there....works real good & dont have to wait a day or more for the wood to dry......usually it dries in about 6 to 8 hrs....
I may try this today for the mirror side.


Thanks for the suggestions. I'll post some new pics on the build page.

Ray
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Old 02-14-2007, 07:21 AM   #8
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I'm building a SA Edge at the moment and Bill Stevens suggests using windex. Thats what I used for the front deck and turtledeck. Both have very tight corners and it did work great. I soaked a folded paper towel and just lightly rubbed a line down the bend radius on the outside of the bend. Waited about 3 mins and made the bend without a problem. It was dry in about an hour. I think that the windex has amonia in it but the wood doesnt seem any weaker now than it was. Anyway, just thought I'd throw that in the mix. Good luck!

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Old 01-02-2009, 03:16 AM   #9
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Do these methods work for 1/4" x 1/4" pieces as well?
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Old 01-06-2009, 05:41 PM   #10
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I've been using windex also for about 20 years.
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Old 01-06-2009, 06:05 PM   #11
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Originally Posted by Tile214 View Post
Do these methods work for 1/4" x 1/4" pieces as well?

Soaking 1/4 squares in hot water for 30 minutes will make them pretty pliable.

Paul
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Old 01-07-2009, 02:47 AM   #12
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OK, I'm a devoted viewer of Discovery, History and other such channels, and from them I have seen where a lot of industries which deal with bending woods a lot harder and tougher than balsa use steaming hot water to bend their woods, sometimes to extremly tight radii.

Has anyone tried steam, nearly boiling or even boiling hot (212 d/F) water?

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Teach a man to build a plane and he'll fly for a lifetime"
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Old 01-07-2009, 04:31 AM   #13
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Yup. Did some boatbuilding back when I had hair, steaming 1x6 cedar planks. If you want to do balsa, any old hot water will do; for the tougher stuff, get a kettle, a length of 2" pipe (PVC, ABS, whatever) stick the wood in with a rag on the end, and plug in the kettle. Just about any wood gives up fairly soon...
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Old 01-10-2009, 12:30 AM   #14
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Originally Posted by pd1 View Post
Soaking 1/4 squares in hot water for 30 minutes will make them pretty pliable.

Paul

Thanks,
Tile
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