Re-warping balsa fins after Windex treatment

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lcorinth

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I'm currently building an Estes U.S. Army Patriot. The balsa fins were slightly - really slightly warped, so much so that if I'd posted a picture of them, you probably wouldn't see it. Still, I wanted to flatten them out.

So I tried a trick I've seen here on TRF. I sprayed the heck out of them with Windex, pressed them under heavy books for a few days, and let them flatten out.

For those who don't know what I'm talking about, apparently the ammonia in the window cleaner can penetrate the wood cell walls, and help to restructure and reshape the wood more effectively than just using water or steam. I'm not crazy about the Patriot, so I figure this was a good rocket to try something new on.

Today, after several days, I took the fins out. The grain was slightly raised in a few spots, but other than that, the fins were nice and flat, and seemed to be completely dry. I sanded off the raised grain, and went to do some stuff for about 30 minutes.

When I returned all of the fins had curled up and warped much worse than originally. If I'm not mistaken, they all seemed to have curled away from the side they were laying on, which might be significant. In other words, they curled toward the exposed side.

I should have taken pictures, but I freaked out a little and threw them all back under a stack of books.

So, what happened there? Is it possible they weren't dry, and curled toward the exposed side as that dried out? Should I have treated them with something else after pulling them out from the books in the first place (like CA or something)?

If they're still curled (or if it happens again) when I get back home, I'll take pictures. I'm just wondering if anyone has seen this happen or knows why this happens. The scrap of warped balsa I had previously tested the Windex trick on flattened out nicely, and never re-warped.
 

BDB

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I have nothing to offer, but that scenario sounds incredibly frustrating. I want to know the answer too.
 

neil_w

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I've had some frustrating experience in that area as well. I'm not sure if it was still wet (shouldn't be after a few days???) or if there is something else going on.
 

lcorinth

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I have nothing to offer, but that scenario sounds incredibly frustrating. I want to know the answer too.
Well, fortunately it happened on this rocket (and I've been playing with some spare fins I cut before doing this, so I can replace them if need be). There's another I'm building that has some warped fins, and I really would like to do a nice job on that one, so I hope to figure out what went wrong on this build before I continue with that one.
 

Steve Shannon

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I'm currently building an Estes U.S. Army Patriot. The balsa fins were slightly - really slightly warped, so much so that if I'd posted a picture of them, you probably wouldn't see it. Still, I wanted to flatten them out.

So I tried a trick I've seen here on TRF. I sprayed the heck out of them with Windex, pressed them under heavy books for a few days, and let them flatten out.

For those who don't know what I'm talking about, apparently the ammonia in the window cleaner can penetrate the wood cell walls, and help to restructure and reshape the wood more effectively than just using water or steam. I'm not crazy about the Patriot, so I figure this was a good rocket to try something new on.

Today, after several days, I took the fins out. The grain was slightly raised in a few spots, but other than that, the fins were nice and flat, and seemed to be completely dry. I sanded off the raised grain, and went to do some stuff for about 30 minutes.

When I returned all of the fins had curled up and warped much worse than originally. If I'm not mistaken, they all seemed to have curled away from the side they were laying on, which might be significant. In other words, they curled toward the exposed side.

I should have taken pictures, but I freaked out a little and threw them all back under a stack of books.

So, what happened there? Is it possible they weren't dry, and curled toward the exposed side as that dried out? Should I have treated them with something else after pulling them out from the books in the first place (like CA or something)?

If they're still curled (or if it happens again) when I get back home, I'll take pictures. I'm just wondering if anyone has seen this happen or knows why this happens. The scrap of warped balsa I had previously tested the Windex trick on flattened out nicely, and never re-warped.
That's exactly what it sounded like; while they were covered they couldn't dry. One you uncovered them and laid them down the top was able to dry, but the bottom couldn't, so they warped as the dry side shrunk. When drying wood you need to make sure both sides get air. That's why sheet goods are stored vertically and boards coming out of the kiln have stickers between them.


Steve Shannon
 

Rex R

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quite likely the fins were not yet fully dry(which is the problem of pressing, no air flow), then you likely put them on a non-porous surface flat. top side dried and shrunk, presto curled up fins. method I use when papering fins, glue/ paper each fin fairly quickly then place on a wire rack(good airflow for both sides), about 2 hr.s later the fins are dry and flat. if not, then I get out the iron, set it to linen and iron them flat, takes about a minute per fin.
Rex
 

aerostadt

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I remember using ammonia water from the hardware store sprayed on large pieces of balsa about 1/8" x 6" x 30". Maybe short fins are different and maybe windex is too weak (The ammonia water smell was very strong). I think that I sprayed one side at a time, then put down aluminum foil on top, and put books on top. After that side was done I did the same thing to the other side. There might have still been some warpage after doing the first side, but after the second was down the balsa was in good shape.
 
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Woody's Workshop

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Did you spray both sides of the fin evenly?
And if you had a solid object both on the bottom and top, it would forever to dry out.
Try putting a couple layers paper towel both under and over the fins.
And only use enough weight to keep them flat.
Excess weight is not needed.
I coat everything with TiteBond II. My fins often curl up on the wet side.
Once they start to flatten out and the glue dries, I flip them over and coat the other side and they usually curl on that side too.
Once the sanding is all done, they are all perfectly flat even if they started out a little warped.
Quick check with a dial caliper keeps them the same thickness from tip to bottom, and from fin to fin.
 

aerostadt

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I coat everything with TiteBond II. My fins often curl up on the wet side.
Once they start to flatten out and the glue dries, I flip them over and coat the other side and they usually curl on that side too.
Once the sanding is all done, they are all perfectly flat even if they started out a little warped.
I have similar experience when papering large amounts of 1/8" balsa with white glue. The first side will warp. Then I turn the balsa over and paper the other side. When things dry out, most of the warping goes away.
 

Micromeister

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While not exactly used on fins, to preshape competition Helicopter duration rotors I've often used Ammonia water to soften the wood while curving the rotors between a fishnet covered PVC Tube and a flexable lexan cover, held with rubber bands. The tight weave fishnet give the ammonia water a track to vent over a couple days. Once the Lexan is removed the rotors are generally bone dry.

you might want to repeat your treatment but add a layer of breathable material between the fins, books and counter top.
 

lcorinth

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Update:

The fins came out just fine. After re-pressing them overnight, they re-flattened. I then pulled them out again, and this time set them on a cooling rack I use to set fins on after coating with CWF (to prevent warping). Even though they were on a rack, I turned them frequently for a while, just in case the little bits where the rack came in contact with the fins prevented any evaporation of remaining moisture.

DSCN3683.jpg

To answer a couple questions and clarify my process:

1. Yes, I did coat both sides evenly. In fact, I sprayed them to the point of saturation, and held them in a small dish while searching for some plastic wrap. There was enough Windex that it covered the whole fin, so it was basically submerged.

2. I wrap them in plastic wrap when I do this. First time I experimented with it, I used waxed paper, but found that the Windex soaked right through the waxed paper. I worried I'd damage my large, perfectly flat books I use for rocket building, so I switched to plastic wrap.

3. I keep them pressed in plastic for over 24 hours. Then I take them out. By that point, they're mostly dry, but not quite. At that point, I press them between sheets of parchment paper. I sometimes use this when pressing fins that have been coated with CWF, because it wicks away some of the moisture and allows them to dry faster than when pressed in waxed paper.

4. A day or so later, I took them out, and then they curled up. But I think you guys are right, there was still a little moisture in them which caused the curling.

Thanks for the input, guys! I'm glad to know this technique works for flattening out warped fins. I did an experiment with warped balsa and water, steam, and Windex, and the Windex definitely did the best job.

Here are some before and after pictures from my test piece.

Before:

DSCN3566.jpg

DSCN3567.jpg

DSCN3568.jpg

After:

DSCN3624.jpg

DSCN3625.jpg
 

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