I was talking to a friend about rodbuilding and bubbles in epoxy. I was actually talking about two part guide epoxy i.e. LS Supreme, when he said he took a model airplane class. He said the instructor mixed like three different epoxies (5 min?), and used to assemble different parts. The epoxies that were mixed carelessly with quite a few air bubbles were substantially weaker than those that were mixed very carefully and didn't have any air bubbles, and they demonstrated that in their class.

Understand that model airplanes and rods are apples to oranges, model airplans tend to be somewhat fragile critters I guess( never owned one), but just wondering if those of us who mix up our rod bond/whatever we use for reel seats, gimbals, etc. rather carelessly since we don't see the airbubbles, are weakening our bonds/joints? Or is the difference in rodbuilding not worth worrying about due to the amount of material covered w/ epoxy?

I think you need to make sure that on rod bond or reel seat paste or any epoxy you are using for glueing up reel seats or cork that the two parts are mixed throughly. On the paste type epoxy you can tell when it is throughly mixed by the smoothness as you mix A and B together. When you first start mixing the paste epoxy it feels stiff as you mix it and as you continue to mix it, it becomes what I call looser but not loose to where it's liquid. So I don't think air bubbles are a factor as much as making sure the two parts are mixed throughly. I hope this is of help to you.

Neal Cissel
Neal's Fishing Products

It is interesting how we evolve in this wonderful but addictive hobby. Two years ago I was not aware, well skilled or meticulous in several areas of rod building. But oh what trial and error teaches us if we watch and remember! Two areas where I very carefully make sure I am thorough and consistant now are : A .... guide foot preparation.... B .... mixing epoxy ( C... cleaning fingers/hands well!) Concerning the mixing of epoxy : careful on equal parts, clean shot glass well, clean spatula for mixing well, ( denatured alcohol), resin first, warm bottles of epoxy a little before hand, warm shot glass a little before hand, PRIME... PRIME... PRIME... once I start stirring the epoxy with the spatula, I stir SLOW and NEVER remove the spatula from the epoxy. Stir for approx. 2 mins or until the epoxy is very clear. I pour it onto a mirror that I have thoroughly cleaned ahead of time. It spreads and levels on its own. There are rarely in bubbles and if a few small ones appear, I give them about a min to get closer to the surface and then I easily pop them with a less than a 10 sec. blow from a straw. I do this using Threadmaster but would think it would work for most epoxies. By experimenting , I found that when I remove the spatula while stirring I was intoducing bubbles and if I stirred faster I tended to create bubbles. My finish work has become very consistant now with this method and in the winter it can often be below zero outside here in Iowa when I am down in my cave working. Find what works for you and then get consistant with it. Good epoxy mixing and solid guide preparation will pay big dividends.

Rod Bond being a past type well have what I call an off clear look an being a past that generates its own heat when mixed. So being a past I do not think that you have to worry about generating a lot of air bubbles mixing. With Rod Bond your measurments can be off a little, without jeopardizing its streangth.
Good Wraps Bob

Sitting here reading Steve's post and thinking about how meticulous I am also. Something I discovered recently while finishing guides with FC regular build. The only time I had bubbles was during application to the guide wraps. I would dip my brush into the spread out puddle on the Al. foil and apply it to the wraps. Now I don't brush it on, I sort of wick it off the brush and lightly spread it. I finally realized, the dipping straight into the FC was introducing bubbles right on to the brush. Now I sneak up on it from the edge of the puddle with brush flattened out and just lift the brush up through it to load it. Sort of like using a spatula. I guess I better try that !

For finish, it is a moot point. For the adhesive side, it's a matter of what works. Any adhesive, in any application, will be weaker with less contact area. The more bubbles that exist in the adhesive, the weaker the joint will be. It comes down to the question of how strong is strong enough? No matter how bubble-free you mix an epoxy, once you start moving parts into position, you have no idea what is going on under that grip/reelseat. Are you breaking any bubbles or are you incorporating bubbles? Bottom line is that if you have a good fit, and a good mix (one that will cure properly), you will have no worries. Then it just gets into a matter of comfort level. I doubt a model flier lost a plane due to epoxy failure alone.

As an example, many folks and mfgrs have been using masking tape as arbors for decades. They work. But if you do side-by-side testing against a solid arbor such as graphite (brick foam), cork, or the new poly type ones, you'll find that the masking tape ones are weaker. The tape is elastic. It moves in the middle no matter how well it is encapsulated. One crack in the epoxy and you are relying on the material, which is not solid. I'd wager that all repairs done on "loose reel seats" are done on masking tape arbors. Overall though, in the real world of fishing, a masking tape arbor is "good enough" and can and will/has last(ed) a long time. I hate using tape as an arbor, but I've done it in a pinch. I've never questioned any bonding epoxy I've used, be it liquid, paste, short set or long set.

I didn't think about that.... Rod bond being a paste epoxy, you don't see very many bubbles in it vs 5 minute Devcon or something to that effect. Agree that finish is definitely a moot point.

Phil,

The mixes with tons of air bubbles in effect put less adhesive between the parts. But as others have said here, how strong is strong enough for what we're doing?

I'd try to do the very best you can with the known best practices for our epoxies. I'd get a water break-free-surface and mix my epoxy adhesive slowly enough that I didn't generate a ton of bubbles, but wouldn't worry over that handful that are just about guaranteed to appear. As you mentioned, we're generally bonding large areas and if you're careful about having good surface preparation and make sure you get adhesive coverage completely on all mating surfaces, you won't likely have any problems.

..............

Phil
I would certainly like to know just how they DEMONSTRATED in that class how a bubble filled epoxy is weaker than a non bubble filled epoxy. I have been trying for years and years to find some method of demonstrating in a class just this same thing. All of my research has told me that you can purposely fill your epoxy's with jillions of bubbles and there is no way on gods green earth you can tell the difference -- for all practical purposes-- between the bubble filled and the solid non-bubble filled joint. I refuse to believe that this issue can possibly be a problem for model airplane builders who deal mainly with a very very fragile balsa wood. Our blanks, real seats, handles etc are far more rugged than the flimsy balsa woods and tissue paper used by modelers. I believe that somebody is blowing smoke rings and using mirrors to prove a point that doesn't even exist.
Ralph

How big a air bubble are you taking about?? I have gluide formica with Rod Bond to a peice of glass and left gaps. I left a 2 inch space at the end of the formica strip so I could have a leverage when I went to remove it. when I tried to remove the the formica from the glass. I broke the formica right at the thin line of RB. I agree with Ralph.
Good Wraps Bob

Ralph- you may very well be correct. All I know is what my buddy was telling me he saw, not sure exactly what they did. It just got me to thinking....

I would be curious if this demonstration took place over several classroom sessions. If in just one session, I would be very suspect of the results.

I've worked with epoxies and polyesters for at least forty years, and all of the guick set products that I am familar with need 24 or more hours to acheive full strength. Maybe there are some that do not, but I am not aware of them.

I am sure it's a ratio thing (bubbles to contact area) but I would think that to tilt it to the point of integrity degradation the mix would have to look like froth.

I have been told that 5 min. epoxy really has no true shear strength. Compared to a slow curie epoxy is that true?.
Good Wraps Bob

Bob,

NOT at all!!

I use 5 min for many things and it holds very well. Just the other day I was trying to replace a butt cap that was put on with 5min several years ago. I had to destroy the cap to get it off!

DR

I used epoxy on wood products many years ago and learned a valuable lesson. With slow curing epoxies, the wood will absorb the A part and the B part differently. I found sometimes, depending on the porosity of the wood, the expoxy never cured. Same effect as poor mixing or off ratio. This problem disapeared when I went to a faster curing epoxy because there was not enough time for either A or B part to soak in. This may have something to do with your friends experience with model plane. Balsa wood is very absorbant.

Bob, in Rodmaker volume 9, issue 5 (if I remember correctly) Ralph O'Quinn pretty much exposed that as a myth. I had also heard that in the past, but never experienced it, and Ralph more or less set us straight.

Gary: How did you apply the A&B. To me it sounds like you applied A to 1 piece of wood and B to another piece of wood and stuck the wood parts together. Am I wrong? Did you not mix the 2 parts together and apply a portion to each piece of wood then put the wood pieces together?
Good Wraps Bob

Royce you are correct I do recall reading that in RodMaker. Thanks for the refrisher. I do not use 5 min. epoxy. So I have no true experience with it.
Good Wraps Bob

Dr.: I just slide a case knife between the butt cap and blank and it pops off. But remember a butt cap and gimble does not receive the twisting and torque stress as reelseats and corks do under the stress of a fish fight.
Good Wraps Bob PS I do have to admit that some builders have had great success using 5 min. when they glue tip tops on. Just my weak thoughts an 2 cents. Just remember no one is wrong and everyone is right. Expressing one’s thoughts or ideas is how we all learn. I learn some thing new every day on this site. Like spelling (LOL)

Bob, I mixed part A & B together just like rod epoxy and applied. This was for outside wood products I was experimenting with at the time. The mixed sample in the container I used would cure fine, but not on the wood. After a little experimenting, I found the A & B parts absorbed differently over time resulting in off ratio mix and incomplete cure.