How does one bend / shape balsa without cracking it .

need ur advise .

Cheers.

Arjun

If you are talking about sheeting a deck, make a mixture of ammonia and water, 50/ 50 will work. Gently wet the outside of the balsa and as it soaks in, gently roll the balsa on to the formers. Once it is place you can ruberband it or tape it or glue it into place. The only thing that you can't do is any sanding until the wood has dryed. Good luck, Dave

When u say Ammonia , do u use absolute Ammonia or say a Windex , which has Ammonia content in it .

Thanks .

Arjun

I have used Windex with ammonia sucessfully...not near as smelly.....

The 50/50 ammonia/water mix if great too....you can use scented ammonia...don't have to use the plain stuff...

My .01675 worth......

In California old or used anahydrous ammonia from blueprint machines is considered hazardous material. The engineering firms who use the machines have to pay some firm about $1 for each gallon to be disposed of. I usually go to the blueprint room of an engineering firm and pick up their old bottles for free, saving them the fee and storage space.

The old blueprint ammonia is really strong, and works excellant as a de-greaser prior to painting. I have dumped it into a large diameter PVC tube capped at one end, then set in balsa sheets to soak for an hour. The sheets are then very easy to bend or curl into position. It is stinky and must be done outside in a breeze. It is cheap, and easier than locating pure ammonia.

Wm.

The nose section of my my 1/6 scale Waco required 3/16" balsa sheeting. I used 50/50 ammonia/water mixture and soaked the balsa over night. I found a large size coffee can that was about the same curvature as the nose. I put the wet balsa sheeting around the coffee can holding it in place with masking tape, then set it outside to dry for a couple of days. As the balsa drys it shrinks on the coffee can not on the plane! When dry, I removed the balsa from the can and had a nice curved sheeting that fit nicely around the nose of my Waco.
-- Jim

Windex with ammonia D works very well

Absolutely nothing wrong with anything that the heavyweight brigade has been posting....3/16 decking sheet - whooowhee!!

If you are like me and work in the lighter stuff - here are some alternative ideas. Most if not all of these will work with up to about 2mm sheet and 3mm soft.

First group - bending across the grain - as in l/e sheeting.

Steam.
Ammonia works good as already described.
Run a damp cloth over the ouside.
Dope and tissue one side, leave to dry for 48 hours, then dampen the other (great for making balsa tubes).

Second group - bending along the grain - as in compound curves etc..

Ammonia is the simplest to start with.
There is a technique that Doug McHard (if I remember correctly) described in Aeromodeller some years back. I have tried it and it does work but it requires much patience and practice. This uses the application of water (lick or spit is best) on the inside of the curve and then the application of heat and bending at the same time. Works on up to 2mm soft balsa.

FWIW...

The ammonia works well. Windex isn't "real" ammonia. It may work but I suspect that's only because the windex wets out very well and soaks in faster.

Also it helps a lot if you pick "bendy" wood right off the bat. A grain I believe is the technical term.

I just sheeted the Turtle Deck of a 27% Extra with 3/32 balsa. Plain ol' tap water worked fine. One thing no one has mentioned... only wet one side of the sheet, the side you wet will become the outside of the arc.

Is the ammonia available for purchase as a household cleaning agent sold in the form of a solution of ammonium hydroxide? If so, what percent (if these manufacturers list the concentration of the their active ingredient)?

I have to bend some balsa tonight and I thought that since I work in a lab, and I have access to various forms of ammonia and ammonium ions, I might just take a small bit of solution home from the lab rather than trek out to the store to buy some.

Any one out there able to give me any insight into what you get when you buy ammonia from the store?

Thanks.

Noah

I have heard the tale of using ammonia. However I have found warm water works just as well. Consider the two attached examples. The first two pics are of a wing still in the bones. The "C" tubing is 1/16" balsa. It was attached to the leading edge with CA before bending. Once in place the outside was lightly wet with a damp sponge. It curved down to shape in seconds. As you can see this is a forward swept wing.. I also realize that this wing was for use in a controlline plane. But the wing itself is about 550sqin area making the size reletive. Consider the next 2 cowl pics. Both were made with 1/16" basswood. This was totally soaked in water for 15 minutes before it was applied to the formers. Once it was dry, the tape was removed and it was then glued to the actual cowl formers. In both cases there were no cracks and no bumps

Balsa does not have much of the lignin and subrin of other woods. It is these that ammonia works on. Ammonia is not necessary with balsa. Water works fine if you can get the balsa to soak it up. Windex or ammonia may help wet the balsa; however, some have reported brittleness after using ammonia. I would suggest just using hot water with a wisp of detergent.

i use hot water to bend balsa...also depending on the curve you need you can also use a cardboard tube to help with the bend....i completely soak the balsa with hot water using a sponge then dry off with a paper towel....i have a 4ft tube about 4-5 inches in diameter and i wrap the balsa(sheeting) around the tubes length using #64 rubber bands...i space the rubber bands about 2" apart from each other and i also make sure the bands are flat against the balsa so there are no marks made from the bands.....i usually only takes 3-4 hours to dry then it's ready to glue

i only have that one tube but it helps for leading edges and turtle decks...i suppose different diameter tubes(cardboard or PVC) will come into play as i begin to build more planes

I also just use hot water for balsa and never had a problem.

BTW, no one has mentioned it yet, but quarter grain balsa really shouldn't be chosen for bending. I mention this for those who don't know that the grain of the balsa sheet has a bunch to do with how it's going to bend. It has always seemed to me that the straight grain sheets work well and any other grain pattern that doesn't look straight and uniform really is going to wind up causing some kind of problem.

And another little trick worth mentioning......

Ace bandage works great. It will press the wet wood with whatever pressure you put into the wrap and not leave compression marks. And it's fabric helps wick the water out of the wood.

I stumbled onto this back when I was a dumb little kid who thought he could play football..... and also wanted to build CL stunters....

Good point Jim.
Most of my bending ( haven't done much building in the last couple of decades) was with hardwoods for guitar bodies. Soaking in plain water and heat were the primary ingredients. Having a good feel for the wood was the determining factor. I guess having a degree in Chemistry and Biology wouldn't hurt either. If wetting is the issue, there are tons of substitutes for ammonia like detergent, borax solution, and probably too many to list (especially in my state at this hour).

I am sort of hippty-hop. I'm building a 1949 CL Dmeco Sportwing. I've built three previous ones and I want to build lighter. So I decided to mold the leading edge. I carved a pattern out of balsa. I'm laminating two pieces of 1/32 balsa to make the leading edge. The width at the rear of the pattern is 3/4 in and the chord length is just under 1 1/2 in, so there is a fairly sharp bend around the leading edge. A three inch wide sheet is just right. The leading edges are just under 18 in long. So I took a nice light straight grained sheet of 1/32 and cut it in half.

I didn't have anything that I could soak a 18 in piece of wood in without a lot of hassle. So here is the good part. On my plate glass building surface, I sprayed a couple of wisps of Simple Green, then sprayed some water and stirred it around with my finger.[:-]. Laid the two pieces of 1/32 sheet down in it and slid them around, then turned them over. Put down a little more water and laid them back down. Idea was to get a bit of Simple Green on both sides. A little more water spray and let them sit a couple of minutes. Limp as could be. Put them on the pattern and they conformed beautiful. Wrapped with Ace bandage. Today removed them, brushed thinned down Titebond between them, put wax paper over and rewrapped. So easy, I am so pleased. Do the other leading edge tomorrow.

get it wet bend it hold it in place with elastics or clamps and let it dry or you can use steam from a kettle but that does pose some hazards

As with the construction of a guitar body, couldn't you rip relief cuts (1/16" deep for 1/8" or 3/16" material) parallel to the direction you want to bend the material, or would this weaken balsa too much?

Need something big to soak in ? try the bath tub, WITH PLAIN HOT WATER. it works real good and its been used on many big proects, beside my body. DICK

I had to bend 1/2 blocks to fit the front taper of a GeeBee. I used my wifes rice steamer, I only had to steam about 10mins each, then I pulled them out and preformed them around by holding them against a round cylinder (a large rool of masking paper I had). The steam drys fast and you can go right to installing when it cools enough to hold the shape. I did 10 4 x 8 pieces this way and not one cracked. If you need a deeper steamer you can use a deep pot with a little water on the bottom and hold the pieces out of the water with a stand of sorts. As it was mentioned above, ammonia does not help much with balsa, it is the water that is doing the work. Also, amonia in the wood will not accept CA glue until it has evaporated completely out where as damp balsa glues fine.

Regards,
Randy

If you are impatient like me you can wet one side under a tap or with a brush. I have a length of 4inch pvc pipe. hold or tape it down and go over it with a hot sealing iron or clothes iron util it is dry.(or nearly so). Instant bend! This seems to first drive the moisture in and then dry it.

Hi friends I use ethilic alcohol, putting the balsa sheet into a plastic bag over night with a little of alcohol, at morning you can bend the balsa as you want, and the cyano glues very well before the alcohol evaporates completely

All great advise, several different ways and methods, to bend Balsa over leading edges, and fuselage tops or bottoms. I usually have to sand the edges for a clean bond and good fit.AJ