Using Cyanoacrylate Glue
by Chuck Howerton?
There are many different glues that are used in the construction of model airplanes. Probably the most popular glue in use is CA or cyanoacrylates [tradenames: Hot Stuff, Zap, Crazy Glue, etc.]. Next in line is the epoxy family and last comes the aliphatic-resin glues.
So which is best? This is not a simple question to answer each has features that make it best for some application and that is what you have to look at. A good aliphatic-resin is probably the best to use if you only have one glue. Titebond and Sigment are two of the brands we find in hobby shops and have been especially formulated to use for model building but plain old Elmers white glue works very well. I use a lot of yellow carpenters glue. The only place these glues fall short is speed. If you have to have it right now it is not the glue to use they can take about 24 hours to fully cure. Second problem with them is that the joints must be tight fitting and should be clamped until the glue sets. If you can live with this it gives a very strong joint a scarf joint glued and clamped this way is stronger than the original piece making it ideal for joining spar stock. I will describe a scarf joint later if you don't know how to do this you are missing something very important.
There is a trick that can be used with this glue that I am sure that you have heard about but I will repeat it here in case you haven't. If you are sheeting a foam wing with balsa, first thin the glue just a bit with water you want it about the consistency of heavy cream Then brush a thin coat on both the foam core and the sheeting. Let it dry overnight then iron it on use any household iron I start with the cotton setting then adjust it as needed to get it to stick down. Experiment just a bit on scrap until you find the right heat range. I also use it to laminate three pieces of 1/16 sheet cross grain to make very stiff and light 3/16 sheets for solid stabs and other parts that need to be cut out of sheet. This is like substituting plywood much stiffer and stronger. I also use it to laminate tips. First make the mold out of thin plywood cut to shape then layer 1/32 strips around the form first soaking them in ammonia and water then wetting them with white glue. Cover the form with wax paper and build up several layers around the form. After it is built up to the thickness you need add a strip of wax paper and tape it tight to the form with masking tape let it dry about 2 days before you remove it from the form It will be very light and strong, cut it to fit then sand to final shape. I also use it to add fuselage doublers in a sheet built fuselage. Brush on a thin coat then position the parts and weight then down until the glue dries Here is a trick I use to keep the parts from shifting while I handle them. Just before I put them together I put 2 or 3 small spots of CA on one piece then join the parts. Hold them for a few seconds and they will never move while you add the weights to hold them down. I use 2 quart freezer bags filled with damp sand for weights. If I need more weight I use 2 bags. Epoxy is another family of glue that is used when you need a lot of strength in a joint. They don't dry in the normal sense they cure by adding a catalyst. They are a two part glue and hold about as well as anything. They can not be used in a high heat situation but are impervious to almost anything after they cure making them ideal for use around motor mounts and any part of the airplane that might come in contact with raw fuel. Acetone is the solvent that is used before it cures after the cure acetone won't touch it so clean up as soon as it starts to kick off. You can buy is in several formulas from 5 minute to 24 hour curing time. The only real difference is the amount of catalyst used. Part A is usually the resin and part B will be the hardener that is the part that will be different. It contains the catalyst and is what governs the cure time. The thing to remember about epoxy is the faster it sets the more brittle it can be. Cure overnight and it will take a lot of abuse but the 5 minute stuff can give up under a lot of vibration like in a motor mount. Anything over a half hour is fine and will hold all right in a motor mount or landing gear the 20 minute stuff is all right as well. It is fine for fuel proofing the inside of a tank compartment and around the firewall . It can be thinned with alcohol or a little bit of acetone and brushed on like paint. I sometimes thin it quite a bit and spray it on with an old airbrush I have If you do spray it be sure to clean up as soon as you finish or us a gun you are going to throw away. Epoxy has the best gap filling properties of any glue that you can use but if you build careful you should have little or no gape to fill. Don't depend on the glue to make up for sloppy building habits.
Now lets talk a little about the CA's. This is the number one choice for most builders. It is fast, holds good , comes in three thickness, thin, medium, and gap filling. There special formulas for use on foam . Why not use it everywhere ? It sure sounds like the only glue you would ever need but it does have some drawbacks that you should be aware of . The fumes can be a little hard on your respiratory system for one thing, and some people are just plain allergic to the stuff. Using the wrong formula can make very week joints, and for large areas it can cure before you get the parts together, worse yet, you have no time to reposition parts when you glue them . It is almost instant bond as soon as they touch. If you use to much accelerator the glue will be brittle and break under load or vibration. And the stuff is just plain expensive . Other than that, it is great stuff. The thicker it is the slower it sets. The thing that I like about it is that I can use a wing jig and almost completely frame a wing before I use any glue at all. That way I can make sure things are the way I want them and then just back and put a drop of CA on each joint. Using no accelerator at all it will be ready to take off the jig by the time I get the top back on the bottle. I put a drop of thin on the end of a butt joint then let it set, then make the joint using thick. The thin soaks into the end grain then bonds to the thick giving a better joint. I also use thin to glass the center section of a wing. Tack the glass in position then with a plastic bag on my fingers I rub thin into the glass cloth like I would epoxy This gives a very strong joint I also reinforce joints this way using a small piece of 2 oz glass cloth and thin CA I just add a glass gusset to each side of the critical joint I have never had a joint of this type fail even in a hard crash everything else might be destroyed but the joint will be intact. I also use it to fuel proof engine compartments and inside tank areas rubbing it on with a soft cloth wet out with glue and just more or less paint it on. Here is a trick you can use if you are painting wood. It makes a great sealer on end grain wood stopping paint form soaking in.
Use CA with plenty of ventilation and use it properly with as little kicker as you need to set it and it will work for almost any application. Acetone will clean it up even after it has set it can also be used for a debonder if you stick to something like your fingers. I am good at sticking fingers together and sticking to parts so I use a lot of acetone. Be careful with the acetone as it to can be hard on you if you breath the fumes. Is CA worth the extra expense and trouble to use? You bet it is, I can now build an airplane in a long weekend that once took weeks to build. No clamping, no pins, no waiting for glue to dry. I buy it in the biggest bottle I can get. I would buy it by the gallon If I could get it. ( I use it for more than building airplanes I do cabinet work and use it all the time) Nothing has done to ease the job of building models more than CA and I will never be without unless something better comes along. But it will never be the only glue that I use. White glue and epoxy will always be in my airplanes where it is needed and should be in yours as well.
Hope this has helped clear up some of the sticky problems you might have had . No big secrets to using glue. Just make the joints fit. I promised you a scarf joint how to here it is. Make the cut along an angle so that the surface is at least 6 times as long as the wood is wide. That means for a 1 inch square the cut should give a surface that is 6 inches long. Glue and clamp with what ever glue is best for the application I use white glue whenever I can and find that this joint is as strong as the orginal piece. Here is a picture that should make it clear.
Chuck
[Note from Fatlion: Some people are extremely allergic to the polymer reaction fumes given off by the curing of CA glues. If you experience 'bad' headaches from use (even momentary use) of CA glues, you might be allergic. The CA allergy appears to be cumulative as well, i.e. the longer you use CA, the worse your allergy get to CA. If you are allergic, don't despair, first try some of the 'Foam Safe', UFO, or odorless types of CA. If the same thing happens, try using Aliphatic glues (Elmers, etc.). I've never heard of anyone who's reported to be allergic to those glues, and they can be really strong and lighter anyway (when used properly).]
Click here to read about what Steve Kerry's experience with CA glue has been.
