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Best method to bend balsa

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Rktman

Eric
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What's the best way to bend 1/16" balsa? I'm trying to bend it into a tube/ring shape. I tried the "soak in hot water for at least an hour" method several times with horrible results each time (really bad kinking, splitting and bending).

I haven't tried the 50/50 ammonia and water method yet. Anyone have any experience with how easy and pliable it makes the balsa? I'm planning on picking up the grade A softer balsa to make it easier but it's beginning to get expensive and frustrating to keep ruining sheets.
 

Incongruent

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What's the best way to bend 1/16" balsa? I'm trying to bend it into a tube/ring shape. I tried the "soak in hot water for at least an hour" method several times with horrible results each time (really bad kinking, splitting and bending).

I haven't tried the 50/50 ammonia and water method yet. Anyone have any experience with how easy and pliable it makes the balsa? I'm planning on picking up the grade A softer balsa to make it easier but it's beginning to get expensive and frustrating to keep ruining sheets.
The grain of the balsa affects the flexibility. Pick balsa that has long grain lines that go along the sheet. (A grain)
 

Forever_Metal

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What's the best way to bend 1/16" balsa? I'm trying to bend it into a tube/ring shape. I tried the "soak in hot water for at least an hour" method several times with horrible results each time (really bad kinking, splitting and bending).

I haven't tried the 50/50 ammonia and water method yet. Anyone have any experience with how easy and pliable it makes the balsa? I'm planning on picking up the grade A softer balsa to make it easier but it's beginning to get expensive and frustrating to keep ruining sheets.
What exactly are you trying to accomplish? what diameter are you shooting for?

If the tube you're shooting for is tighter than say 2" diameter I'm thinking balsa will usually crack along the grain no matter what size and how much prep is used. I have seen some rather thin veneers get rolled like that but it's hard to get any strength out of them. The amount of adhesive and the bracing required would probably defeat the purpose of using it anyway.

fm
 

Rktman

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Thanks, already planning to get the softer/more flexible "wimpy stuff today. It's the method I'm more concerned about tho (ammonia soak? some other chemical to soften?)
 

Rktman

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What exactly are you trying to accomplish? what diameter are you shooting for?

If the tube you're shooting for is tighter than say 2" diameter I'm thinking balsa will usually crack along the grain no matter what size and how much prep is used. I have seen some rather thin veneers get rolled like that but it's hard to get any strength out of them. The amount of adhesive and the bracing required would probably defeat the purpose of using it anyway.

fm
Forever_Metal

The initial size would be 4.50" and final size 5.0" (allowing a couple inches of trim-off for the stubborn ends which always refuse to conform to a mold).
Making a balsa ring-tube, which I've seen done supposedly only with hot water (3 tries later and I can assure you it doesn't work even after 3 hours of 210 degree heat).
 

neil_w

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My balsa bending adventures are described in another thread. I used two layers of laminated 1/16" balsa (a fairly dense piece, also) to create extremely strong 1/8" curved pieces. I wet my pieces down with Windex, then soaked in hot water for an hour or so, and then secured them to my form. My pieces, however, don't have as much bend as you're shooting for.

When I was researching this originally, I saw one recommendation (on an airplane forum) to laminate layers of 1/32" balsa. I couldn't find any of that stuff locally, which is why I ended up with my 1/16" sheet, but I still took the approach of laminating thinner sheets, which really works well. In your case, you may find 1/32" sheets will bend to your will (sorry) much more easily. And the multiple laminated layers will result in a very strong piece that will hold it's shape when you're done. I think you're much more likely to succeed that way then trying to bend a single sheet into a loop.

BTW, if you want a 5" diameter final result, then I can recommend 4" PVC couplers as a form. They're ideal and pretty cheap.

Good luck!
 

Rex R

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I have managed to bend balsa to make a ring fin, end result was heavier than a paper tube. people do bend wood but, they use steam to heat the wood. you want to use the thinnest wood you can find. last ring I made I used 1/64" ply...I would suggest using paper to make your ring, two or three layers of cardstock makes for a fairly sturdy ring w/o all the muss and fuss(and odar) of soaking wood in ammonia :).
Rex
 

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I've done 3" dia for wheel wells on R/C aircraft, and with 1/16" balsa. it is possible. As mentioned, the gain quality makes a difference. I would also think that the length of the part will impact the ease of bending, but not by much. get the really light soft stuff..

Now, we are all assuming you are bending / wrapping perpendicular to the grain, and not parallel to it (if you're making a cylinder, the grain is along the cylinder's axis, not parallel to the upper & lower edges)

You also might want to look at 1/32" ply or even a few layer of 1/64" ply (yes, the stuff exists!) for your ring fin..
 

Rktman

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neil_w dr wogz I found some soft A grade balsa and will give it one more try using ammonia and a 1 hour hot water soak. Unfortunately the only craft/hobby shop balsa I can get has grain running parallel to its length, not perpendicular to the bend direction. That really makes it resistant to being shaped into a cylinder. (Using a 4" OD PVC coupler as the form).


If the ammonia/hot water treatment doesn't work I may just throw in the towel and maybe use the suggestion by Rex R to roll a paper ring instead. After 3 attempts and destroying 3 balsa sheets it's getting too frustrating and costly...
 

Incongruent

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neil_w dr wogz I found some soft A grade balsa and will give it one more try using ammonia and a 1 hour hot water soak. Unfortunately the only craft/hobby shop balsa I can get has grain running parallel to its length, not perpendicular to the bend direction. That really makes it resistant to being shaped into a cylinder. (Using a 4" OD PVC coupler as the form).


If the ammonia/hot water treatment doesn't work I may just throw in the towel and maybe use the suggestion by Rex R to roll a paper ring instead. After 3 attempts and destroying 3 balsa sheets it's getting too frustrating and costly...
Maybe you could try 1/64 inch plywood.
 

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you will want to wax or wax paper your form so that the glue doesn't stick to it. white glue works very nicely on cardstock.
Rex
 

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If it's PVC being used as the form, I don't think you need to cover it. White or yellow glue really doesn't stick to it. Although wrapping in waxed paper certainly can't hurt, if you make sure it's nice and smooth underneath there.
 

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You could consider a hybrid approach, one layer of cardstock on the mold, then glue very thin strips, like stringers, of balsa around the circumference. You are basically laminating the ring circumferentially with the balsa strips. The cardstock underlayment gives you something to glue them all to as you work your way around. Kind of like how a barrel is formed from a set of planks, just with thinner planks.
 

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I've used the spray bottle method with success on several projects. Basically you spray one side of the balsa with water. That side will expand and curve. Hold that curve( over bend it a bit) until it dries( it will spring back some). repeat the process and BE PATIENT! If the wood your using has a " hard line" in it, it may break or fracture--that's just part of the deal! You can use this to make "against the grain " curves as well, although the radius is much larger but the parts are quite strong! When your done , a coat of resin on the outside curve will help to hold the shape and strengthen the wood. After it sets, coat the inside.--H
 

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To echo what others have already said on this thread, use 1/64"-thick plywood.
 

Rktman

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you will want to wax or wax paper your form so that the glue doesn't stick to it. white glue works very nicely on cardstock.
Rex
Thanks for the tip!
 

BABAR

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Sorry

I am still lost at the, "why"?

If the end product is a ring fin, rolling with card stock is likely to be easier, lighter, and more durable.

Also, any chance a round Quaker Oats carton (maybe double or triple laminated) might fill the bill?
 

Rktman

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The low thickness makes it much easier since there's less stress on the outer side.

No water used and little pressure:
Unfortunately I'm trying to bend it the long way, parallel to the grain,to form it into a ring.
 

Rktman

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Heres what I did. See #5 in link. I also papered them after. I think this was 3/32.

I just dampened the wood a little and then bent it around the rattle can and held it on with bands.
OH.YA.. I also decided it would be much easier to make them in two pieces, glued together and then final shaping.


https://www.rocketryforum.com/showthread.php?10745-Absolute-Zero&highlight=Absolute

Nice build, very cool! I think part of my problem is trying to bend a complete ring in one go. The ends just stubbornly refuse to curve and usually the last 4 or 5 inches kink badly or break. Partial bends (not a complete 360°) seems entirely possible though, as at least part of my sheet curves okay.
 

Rktman

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Sorry

I am still lost at the, "why"?

If the end product is a ring fin, rolling with card stock is likely to be easier, lighter, and more durable.



Also, any chance a round Quaker Oats carton (maybe double or triple laminated) might fill the bill?

If this last attempt doesn't work I'm definitely switching to rolling my own paper tube. It's actually for a glider so weight and final ring diameter was a concern. Anyway, I found some really soft lightweight A grade balsa yesterday and wrapped it around the form using elastic ace bandages. One end started to kink but I won't know the final results till it's dry and I can unwrap it.
 

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What's the best way to bend 1/16" balsa? I'm trying to bend it into a tube/ring shape. I tried the "soak in hot water for at least an hour" method several times with horrible results each time (really bad kinking, splitting and bending).

I haven't tried the 50/50 ammonia and water method yet. Anyone have any experience with how easy and pliable it makes the balsa? I'm planning on picking up the grade A softer balsa to make it easier but it's beginning to get expensive and frustrating to keep ruining sheets.
Yes! 50/50 ammonia water method works like a dream. I use it with one of several PVC pipes to curve Competition Helicopter Rotors and Glider wings. I've found adding a nylon small opening fish net under the Contest Balsa and .005 Lexan cover sheet give the Water solution an escape route letting the balsa dry overnight. without the fish net it usually took 2 to 3 days for the balsa to dry and Set. Once dry these Rotors or wings retain their curvature permanently.

I can also 3rd James duffy's suggestion about using 1/64" or 3/64" 3-ply Aircraft plywood for making Large rings and Transitions. The foamcore hollow Fins and Very Long Transition on my 3X Up-Scale Laser-X are 3/64" 3-ply Plywood. Cold Rolled without any chemical or water necessary. The transition is BT-101 to BT-60.

MM 215b1b-sm_Free Hub rotors up_05-08-05.jpg


MM 215b1d-sm_FreeHub Rotor Tip_05-08-05.jpg
 

Rktman

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Yes! 50/50 ammonia water method works like a dream. I use it with one of several PVC pipes to curve Competition Helicopter Rotors and Glider wings. I've found adding a nylon small opening fish net under the Contest Balsa and .005 Lexan cover sheet give the Water solution an escape route letting the balsa dry overnight. without the fish net it usually took 2 to 3 days for the balsa to dry and Set. Once dry these Rotors or wings retain their curvature permanently.

I can also 3rd James duffy's suggestion about using 1/64" or 3/64" 3-ply Aircraft plywood for making Large rings and Transitions. The foamcore hollow Fins and Very Long Transition on my 3X Up-Scale Laser-X are 3/64" 3-ply Plywood. Cold Rolled without any chemical or water necessary. The transition is BT-101 to BT-60.
Curving it across the width of the balsa piece vs curving it along its length seems to be far easier, especially with such a severe bend as I'm attempting (360° ring). I'm discovering that the old 2003 plans I'm working with are full of inaccuracies.


On a related note, does curving your rotor blades take the place of having to airfoil them? I just scratch built a self-designed Helicopter and spent days airfoiling the rotors. They turned out beautiful and the maiden flight turned out far better than I expected, but if curving the blades will give the same results as carving, I'd rather go that route.
 

Incongruent

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Unfortunately I'm trying to bend it the long way, parallel to the grain,to form it into a ring.
Plywood comes in large sheets, so you can cut the piece with the optimal grain orientation.
 

ayryq

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I bend balsa all the time, just glue a sheet of paper to one side of a flat fin :)

...but seriously, I would suggest you need to overbend it, this is what is done in "woodworking" - you need to wrap it to a tighter diameter then the final product so when it springs off the form it's about right. Probably easier to do two halves and join them.
 
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