Wood bending techniques - RC Groups
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Oct 07, 2017, 11:09 AM
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Wood bending techniques


Finally found this old Model Builder article about bending wood. Use it wisely, children. Share where ever you like.
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Oct 08, 2017, 09:03 PM
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Very interesting article although he kind of downplays the handling hazard of aqua-ammonia. Household ammonia is a 5-10% solution of ammonia and aqua-ammonia is almost a 30% solution. It is very caustic and to use it without a face shield and rubber gloves is foolish. It's use is possible but you must be careful and handle it like the lab chemical it is.
Oct 08, 2017, 09:38 PM
Registered User
I would concur. Safety issues are more prominent these days, and rightly so. However, I used to work in the "custodial trade" and remember buying ammonia this strong as a matter of no great concern. What I take from this article is that household strength ammonia is pretty much useless as a wood bending agent, aside from the fact that it may wet better than plain water or perhaps being available in a convenient spray bottle.

I see possibility of one piece wing tips and fairly complex fuselage shells, molded in balsa, using these methods. Probably at extreme limit of home fabrication methods, but still possible, with forethought and reasonable care taken during all processes.
Oct 08, 2017, 09:45 PM
Registered User
Dunno..... Household Ammonia has been Pretty effective in My wood bending adventures.
Albeit on Balsa only, Sheets and sticks though.
A Blu foam plug, a sheet of Well cured in Ammonia Balsa ,a Tensor bandage and next day a Half shell results
Suspect the % strength of buy at the store Ammonia is likely .... Variable.
Some generics are seriously odourus, some name brands barely so. Simple whiff test before buying.
There was some talk about ammonia bent/shaped wood being of reduced strength as result.
No Idea.. merely heard it said.
Last edited by Bare; Oct 08, 2017 at 09:51 PM.
Oct 10, 2017, 01:29 PM
B for Bruce
BMatthews's Avatar
There was another article in Model Aviation either when it was Model Aviation or perhaps back when it was American Aircraft Modeler. In that article it focused on the idea of actually molding compound curves from the wood using "2x strength" industrial cleaning ammonia. Along with the article on forming the wood there was a plan for an RC sailplane that used a fuselage with a lovely compound curve shape that was done over a wood form using this method. The results being pretty much what Bare just described.

The claim in the articles was that once the ammonia fully dries away the lignum should still all be there. But since the ammonia softens and then dissolved the lignum I suspect that the best strength would be from a shorter exposure time. In fact with the seriously strong 30% stuff I wonder if just letting it soak in the fumes would work?

I've never got around to doing a half or even quarter shell molding. But I've used it for making laminated strip curved outlines a few times over the years. And there's no doubt at all that the ammonia makes the wood WAY more flexible so I can use less layers of thicker wood to get the sizes needed with less glue lines.
Oct 10, 2017, 02:05 PM
Registered User
There was another article (sorry can't recall which mag), back in late 60's about how to mold sheet balsa fuselage halves, like Top Flite was then doing for their 1/12 scale (C/L) P-51D kit. The bending agent was plain hot water. I carved a P-51B forms and gave it a try. The shells so formed were a limited success.

Years later I had opportumity to make formed 1/16 ply LE covering for a full size aircraft. We were using mahogany 3-ply and read many article about steam bending etc. Steam certainloy worked but left neasrly no handling time one removed from steambox. 30 seconds wassimply not enough to form the ply over the mold and then strap it down. Later, we found simple soaking for 3-4 hrs at room temp. ideal. There was no advantage letting it soak longer. Any less and the desired softness/limp factor was not attained. Working time was 15 minutes but after 10 minutes the ply would begin to stiffen. you coiuld see it and feel it. After 15 min the wood regained its original stiffness and would not take the desired set. I have no doubt some compound curvature is possible with this "cold" method.

I would like to give it another try, using aqua ammonia process.

"loss of strength" is more of a gut feeling, rather than a quantifiable/practical reality. We choose a piece of balsa for a particular use based upon our experience and a visual. We cannot look inside each piece for any weakness or comparative disparity. Same is true of building full size.

Wiff test of higher(than household strength) concentrates of ammonia is simply not wise. It can a literally knock you out! Makes your head feel like it's going to explode!
Oct 10, 2017, 06:39 PM
Registered User
I have recently discovered both balsa and bamboo can be bent nicely using a variable temperature soldering iron. The bamboo can be bent dry and balsa soaked in water until it becomes more flexible. A bit of experimenting will find the temperature that allows bending without charring the wood. I bend longerons for old time rubber models which many times lack diagonals to help hold the shape. Works well for me without harmful chemicals. Still trying to figure out what I would use a corkscrew shaped piece of balsa for...
Oct 10, 2017, 07:03 PM
B for Bruce
BMatthews's Avatar
Quote:
Originally Posted by packardpursuit
......."loss of strength" is more of a gut feeling, rather than a quantifiable/practical reality. We choose a piece of balsa for a particular use based upon our experience and a visual. We cannot look inside each piece for any weakness or comparative disparity. .......
To some extent I do this on small section strip stock used for "serious" building such as the main longerons on stick built fuselages or those that use formers and stringers and are then covered with tissue, fabric or films. I "test snap" a sample and look for a ragged break with a good density of long fibers in the break. Poor wood with horrible flexibility and strength tends to snap with clean flat faces that almost look smooth and wavy like glass. But usually there are SOME fibers but not enough for more critical applications.

It's not hard to find such good fibrous stock when working with the heavier density grades of balsa. But it becomes quite hard to find such wood when working with lighter contest or near to contest grade density wood. Each sheet I find is carefully doled out over the parts of a project that really need it.

Anyway, now that the stage is set it should be possible to cut away some samples and use them as a comparison. Treat some of the scraps to the same exposure of ammonia and then after it all dries, including the parts being molded, test snap some of the samples that were and were not soaked in the ammonia. The feel for the strength needed and the look of the breaks should give one a pretty good idea on how it worked pretty quickly.
Oct 14, 2017, 11:16 PM
Balsadustus Producerus
Had a high school student in drafting class ask that question...Is the ammonia used in the blueline machine the same as his mom used at home? Before anyone could do anything to stop him, he unscrewed the cap, stuck the open top directly under his nose, and took a very deep breath. Fortunately, the drafting teacher was right there and caught the student as he went down.

That day, we learned in drafting class, if you wish to sniff test something, cup your hand, wave it over and near the substance and bring it to you. An alternative, is turn the container so as to wet the top/cover/lid/cap and carefully sniff that. From a distance. Not up close.

Trivia. Most polyurethane paints use polyisocyanate as the curing/hardening agent. If you can detect the smell at all, regardless of any protective gear, OSHA says you are about 200% over exposure limits for that day.

Tom Hunt had a VHS tape on molding balsa, but I've never tried it to that extent. Gotta do that, someday.
Oct 15, 2017, 03:49 PM
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jumo004's Avatar
Quote:
Originally Posted by Balsabird
Had a high school student in drafting class ask that question...Is the ammonia used in the blueline machine the same as his mom used at home? Before anyone could do anything to stop him, he unscrewed the cap, stuck the open top directly under his nose, and took a very deep breath. Fortunately, the drafting teacher was right there and caught the student as he went down.

.


Amazing, I had a similar experience back in the 60's. I was an apprentice draftsman and part of the apprenticeship was running the blue print machine.
One day I had to change the ammonia bottle but before I did I stuck my nose in and took a whiff ..... it sent me back about 3 feet and I hit the wall and slid down and landed on my butt.
Man oh man !


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