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Glueing Balsa, CA or Wood Glue?

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Old 05-25-2004, 04:31 PM
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sharkbite
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Default Glueing Balsa, CA or Wood Glue?

It seems that most kits recommend using CA to glue balsa structures. Is it better to use CA to tack(spot) glue joints together then comeback with wood glue to offer better penetration, joint strength and flex to the plane?

Does CA become brittle after a certain period of time whereas the wood glue won't?

Also, if one plans to fiberglass, does CA or Wood Glue react with resin?

Any thoughts from some of you expert plane builders can lend would be appreciated!

P.S. I am starting out with a Goldberg Super Chipmunk and want to use the most proven construction techniques when it comes to glueing joints.

Thanks!!!
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Old 05-25-2004, 05:29 PM
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JWN
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Default RE: Glueing Balsa, CA or Wood Glue?

>It seems that most kits recommend using CA to glue balsa structures. Is it better to use CA to tack(spot) glue joints together then comeback with wood glue to offer better >penetration, joint strength and flex to the plane?

This topic is nearly as opinionated as religion. Everyone seems to have their own special technique. I personally use a whole slew of different glues, but primarily use CA by itself. You can tack with CA then follow up with alphetic if you like, but I personally do not feel it's necessary with our models. If the parts fit together tightly, almost any glue is strong enough that the wood will break before the glue joint fails/

>Does CA become brittle after a certain period of time whereas the wood glue won't?

Some brands are more likely to than others. Old glue is also more likely to cure brittle.

>Also, if one plans to fiberglass, does CA or Wood Glue react with resin?

No, there is no reaction.

>P.S. I am starting out with a Goldberg Super Chipmunk and want to use the most proven construction techniques when it comes to glueing joints.

Make sure all joints are tight and use whatever glue you prefer. You won't have any problems and the model will last for many years.

John
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Old 05-25-2004, 06:37 PM
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spokman
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Default RE: Glueing Balsa, CA or Wood Glue?

One thing to keep in mind is that Thin CA does not bond lite ply well. I like to use CA for tight balsa joints. Tightbond II for gluing lite ply. Medium CA for lite ply that needs to use CA. Such as a fuse assembly where you need some wicking action. I like really like the wood glue though. It dries very fast for me. Around an hour and I can handle the parts if careful. I'm just starting an SE. I'm planning on using wood glue if I'm almost ready to stop or I can go onto other things. One thing I noticed with wood glue is that it will shrink as drying. Not a great gap filler. One trick is Thin CA with baking soda. Put the baking soda on first. Blow it, brush it, shake it into position. Don't get to close, apply thin CA and you have a rock hard bond. This stuff doesn't sand well so be careful. Even small particles will bond and make sanding a pain. Anyways, get some of all the glues, by the end of the plane you'll be reaching for the best glue. My last plane has CA, CA+, Tightbond II, Epoxy and Gorilla glue on it.
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Old 05-25-2004, 07:21 PM
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Default RE: Glueing Balsa, CA or Wood Glue?

thin CA esp. will become brittle with time.
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Old 05-25-2004, 09:36 PM
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Default RE: Glueing Balsa, CA or Wood Glue?

Over the years , I've lost my tolerance for CA fumes. I went back to Tite Bond II and it is really very good. I recently picked up a 40 Super Sportster in a trade and was amazed at how much thick CA there was smeared all ove the inside of the thing. The main rule is that if a little glue is good, a ****load is not great.

The thin CA works great on tight fitting balsa joints. The medium is nice for not-so-tight joints. Putting wood glue on top if CA doesn't make any sense to me. I fit everything well, pre-glue my end grain, and am very happy with the Tite Bond. BTW, CA does not evaporate, so weight builds up fast if you don't pay attention.

One of the best custom builders I know buys regular Elmer's white glue by the gallon and uses only it with the exception of some epoxy.
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Old 05-25-2004, 10:59 PM
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Darren40
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Default RE: Glueing Balsa, CA or Wood Glue?

I use several different glues depending on the joint. I find a tight CA joint to be stronger than the same joint using wood glue. Wood glue doesn't penetrate as well as thin CA does. A tight joint with soft balsa is ideal for thin CA and will be stronger than the wood around it. Don't worry about the joint being able to flex, let the structure between the joints do the flexing, not the joint. Its tempting to let the CA wick into the wood around the joint, but this adds weight so don't do it if weight is a concern. Don't have your face directly over the CA glued joint because when it 'goes off' the fumes can be irritating and there are several people who have developed an allergic reaction to the stuff. I use aliphatic resin (a wood glue) when I'm going to have to sand the joint later because CA is too hard. I also use aliphatic resin to laminate wood since it gives you time to position and clamp, and is lighter than doing the same with medium CA. I use epoxy on hardwood rails or plywood, especially butt joints or where strength is important. Putting wood glue over a joint which has been tacked in CA doesn't make sense to me either. I haven't experienced CA getting brittle on my planes, and I've been in the hobby for almost 25 yrs. I've seen a really good site somewhere on the web from one of the CA suppliers that discusses CA glues in detail and the differences between thin and thick CA and how shelf life affects bond strength. Nothing to worry about with CA or wood glue if you're going to fiberglass. If you're new to fibreglassing check out the onfo available on using Polycrylic on .6 oz cloth as an alternative to the polyester and epoxy resins used for this purpose. Its far easier to work with, and lighter, but use a sanding sealer first. Lastly, realize that there is differences in the quality of CA or of wood glue, so pick reputable brands.
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Old 05-26-2004, 07:34 AM
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Default RE: Glueing Balsa, CA or Wood Glue?

The parts fit on modern kits is so good that the basic structure of a wing can be assembled first, then CA applied. In fact, some manuals have large warnings "Don't glue until we tell you to". This is so you won't end up with a warped wing, or they intend for you to jig in washout before gluing. Wing and deck planking have also been eliminated in many kits.

Whether kit or scratch, if built carefully there should be no gaps. I use epoxy on all formers, firewalls and ply braces.

If you plan to have planking on the decks or wing, then you need aliphatic. But there is a trick that the directions don't mention. You must "double glue" all balsa parts. Just applying once to both surfaces and joining isn't sufficient. Planking needs to be pre-formed/fit and dry before gluing. Aliphatic doesn't wick into joints, so applying after tacking with ca doesn't serve much purpose except to add weight. Adding additional beads of glue on top of the joint is like pouring oil on the outside of your car engine.

Aliphatic is good for laminations, but you have to clamp immediately as it bows the wood.
If you perforate or cut lightening holes in the laminations, then you can use CA. My fuse doublers look like swiss cheese. Once I weighed all the cutouts, over an ounce saved. On a light plane, that amounts to a 20% reduction in weight. I recently built a 25 size Kaos type, total airframe weight was only 20 ounces.

For the average 40 size plane, the total glue used will be about 1 ounce more or less, and more isn't always better. From the looks of some ARFs I've seen, I think they pre-assemble the entire plane, then dunk it in a vat of glue.

BO
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Old 05-26-2004, 10:50 AM
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Default RE: Glueing Balsa, CA or Wood Glue?

Thanks for the tips on the glue. I was also considering dovetailing joints for adding strength and pinning. May be a little overkill, but the plane would be extremely solid and last for many years. Thanks again for the helpful information!
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Old 05-26-2004, 05:23 PM
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Default RE: Glueing Balsa, CA or Wood Glue?

I think dovetailing the joints would be a bit excessive. This design has been around long enough to have worked out any structural inadequacies. In fact, if anything, the design is a bit on the heavy side. There are a lot of areas you could remove weight through lighter materials.

just my .02

John
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