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Straightening Balsa

Old 03-02-2021, 01:24 PM
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RKTLaunch
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Default Straightening Balsa

I'm not having any success straightening a 1/2 x 3/4 x 36" stick. I've talked to tech at balsa distributors. Wet it, clamp it with small shims to bend it in the opposite direction. I'm not getting improvement. Tech told me don't worry, after gluing the wing, it'll stay straight. I don't believe that. It's a leading edge. I bought 2, one stayed straight, one bent...1/4" down the length.

I have to buy several and hope I get some that stay straight?
.
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Old 03-02-2021, 01:28 PM
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solentlife
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I heard that ammonia based window cleaner is better than just plain water ...

But yes normal method is to wet and clamp in opposite direction ... let it dry ..
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Old 03-02-2021, 03:52 PM
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Originally Posted by solentlife View Post
I heard that ammonia based window cleaner is better than just plain water ...

But yes normal method is to wet and clamp in opposite direction ... let it dry ..
Yes, I used window cleaner.
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Old 03-02-2021, 05:33 PM
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firemanbill
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I mix ammonia in distilled water about 50/50. put it in a spray bottle and soak her down. then do that opposite bend thing. Just like pretty much everything else in building, be patient, take your time.
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Old 03-02-2021, 05:49 PM
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Wildflyer
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I know this will sound a little drastic, but I had to straighten a piece and didn't want to take a lot of time.

I cut the piece with a knife down the middle, then glued them back together while holding it a straight line or a tiny bit over bowed.

Worked great for me, It was a main line deep spar with a serious bend.
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Old 03-02-2021, 08:09 PM
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Originally Posted by Wildflyer View Post
I know this will sound a little drastic, but I had to straighten a piece and didn't want to take a lot of time.
I cut the piece with a knife down the middle, then glued them back together while holding it a straight line or a tiny bit over bowed.
Worked great for me, It was a main line deep spar with a serious bend.
Not for a leading edge. It'd make one wing heavier then the other. Otherwise it might be ok in other places.

Originally Posted by firemanbill View Post
I mix ammonia in distilled water about 50/50. put it in a spray bottle and soak her down. then do that opposite bend thing. Just like pretty much everything else in building, be patient, take your time.
I just used windex..I had laying around. I might try your mix.

Yeah, this time I waited almost 4 days to unclamp it. It came out better. Opposite bend thing?...oh you mean to straighten it.

I don't know, if I buy 10 of them and let them set a couple weeks, I'll find out which ones will stay straight....but I'm not to that point yet.
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Old 03-02-2021, 08:36 PM
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solentlife
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Wood has cellulose in it and that works with the ammonia ... water etc.

An old trick was to paint water one side and dope other ... the sheet or spar would warp to the dope side as it shrank.

More tricks : On boats that have wood rubbing strakes screwed to the top of hulls - you can imagine that to bend such wood to fit the curved hull needs a system to avoid snapping the wood .............. the way its done is a centuries old trick :

A long tube is laid not quite horizontal with one end fed steam from a small boiler - you'd be surprised how little steam actually is needed .... the other end of the tube has a removable cap with a hole in ...

Get the boiler going .... feed in the lengths of wood (make sure you have suitable lines attached that hang out of the end of tube) ... replace cap ...
Steam should basically warm up the tube till wisps of steam exit the hole in the cap ....
You need 'oven gloves' to extract the wood ... and depending on how long you leave in the tube - determines how pliable the wood is .... then wood is clamped one end to boat and then bent round the hull and clamped at other end ... going back along length clamping where needed ... then fastenings progressively from bent end working back to straight end. Once fastened and cooled - clamps removed.

OK - why tell this ? Take the L/E spar and then keep passing it back and forth through the steam from an old style kettle or pan of water on the stove ..... keep basically going till the wood is 'pliable' ..... now clamp it such that its bent slightly opposite to the warp. This time SLIGHTLY because the steam will make the wood more 'correctable'. If necessary repeat ...
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Old 03-03-2021, 12:12 AM
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Yes, I needed to steam some sheeting...once a long time ago. I discovered I could tightly bend smaller sheets by boiling it. it worked and was much easier. Didn't harm either 1/16th or 1/8th balsa...pieces of cut from sheeting.

I bent it around 1.5" PVC pipe and clamped it, with gavaninzed flashing between the clamp and balsa.
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Old 03-03-2021, 12:00 PM
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ron_van_sommeren
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Heat and ammonia 'soften' the lignine in the wood, water 'softens' the cellulose.
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Old 03-04-2021, 01:36 AM
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[QUOTE=RKTLaunch;1028516]Not for a leading edge. It'd make one wing heavier then the other. Otherwise it might be ok in other places.

I don't use anywhere close to enough glue to "make it heavier"
After the excess is squeezed out, you would have to use a laboratory scale to detect it. Their are many things that will make a plane a touch heavier on one side than the other.
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Old 03-04-2021, 10:11 AM
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Most models have one wing heavier than other ... or when putting LiPo / RX etc. in - slightly offcentre causing 'one wing low' .... especially on small models !

Solution ? Small nails / tacks into lighter wing tip to correct. On really small models - blob of epoxy or similar.
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Old 03-04-2021, 04:03 PM
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It bent back. I ordered 6 more. Maybe a couple will be straight.
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