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