Paul S.

Yes I see, well I just wanted to make a successful go at it, CA is like crazy glue right?

Paul

Paul S.

Yes I see, well I just wanted to make a successful go at it, CA is like crazy glue right?

Paul

piper_chuck

My Feedback: (12)

Yes, but there are many different formulations, stick with the hobby varieties.

piper_chuck

My Feedback: (12)

What is "milled fiberglass"? Just kidding. I have several big pieces of fiberglass cloth in the shop. If I end up with small scraps, I cut them up and add them to a small container that I keep full of the stuff.

acerola

According to TowerHobbies specs page, Devcon 5 min epoxy can hold a pressure of 1500 PSI, and 30 min epoxy can hold 2500 PSI. So, it is much stronger.

NHP epoxies have different timings. For example:

Working Time: 10 min.
Sets In: 30 min.
Can Be Handled In: 2 hrs.
Curing Time: 8 hrs.

Also, there is a 3 hours epoxy, that gives you 45 min of working time:
http://www2.towerhobbies.com/cgi-bin...&I=LXBH70&P=ML

maxpower097

I like 6 min epoxy makes really good filler and you can start sanding it in an hour. Plus its gonna be more air tight siliconish then and CA.Thus it will give

Liberator

Other than working time for me the big difference is that 5 or 6 minute is a lot more brittle after it has been cured then 30 minute. This can make a difference on firewalls and the like where vibration is more of an issue.

cdub50

Rodney, in an earlier response, got it absolutly correct. It is a molecular bond, longer chains are formed during the longer cure times. And that is what gives it tensil strenth as well. You cannot get that with CA.....so that is why for the items of significant stress (engine firewalls, wing joins etc), they say use long curing epoxies.

Not to say you may not have had success with CA, in fact many do. Epoxies however are stronger, more flexible, over the long run.

Cdub

kzimmerman

I have been using various formulations of epoxy in an industrial setting for about ten years now, and i have seen alot of funny things done by hobbyists with epoxy. But, the gist of epoxy is this: Epoxy must be mixed in the exact quantities to fully cure, ie. adding more "hardner" will not make it cure faster. The longer the working time of the epoxy, the stronger it is, and the more it penetrates into the joint, resulting in a longer lasting bond. The elasticity of epoxy is more a result of it's formulation, and will vary from manufacturer to manufacturer.

Is this important for us? I don't believe that it is, as the joints that we use epoxy on don't have that high of a strength requirement. For us, it's more a function of working time, and joint preparation. A joint that goes together cleanly and with little gap will always be stronger than a wide open one. Also, with epoxy, you need to make sure that you get good coverage on both surfaces being glued, as this allows the chains to form across the pieces, glueing them together. A definite advantage that epoxy has over ca's is gap filling. Ca's just don't have the gap filling strength that epoxy does.

So, in conclusion, take what I said, use what U want, we can argue the merits of diferent glues until we are blue in the face, but were all gonna use what we want.

richrd

[quote]ORIGINAL: kzimmerman

Is this important for us? I don't believe that it is, as the joints that we use epoxy on don't have that high of a strength requirement. For us, it's more a function of working time, and joint preparation.


your on the right track kzimmerman
I was thinking as I read these testimonials about 5 minute epoxy and 30 minute epoxy being of different strengths. Use the 30 minute in the high stress areas … in balsa designs how can their be any area of 1500 psi requirements. I mean if I stood on my wing with 5 minute epoxy used in the wing jointer area no way will the jointer epoxy break first. So what if 30 minute is twice as strong the balsa it’s just so over kill at 5 minute strength. It’s just the time you want to work with, also the penetration is so small to think about … the shear at 20 % into the wood or 80% into the wood is still sheared and broken. To lead people to believe their wing or tail feather is going to hold up longer with 30 minute is miss leading. IMO Rich

JohnW

My Feedback: (6)

On Milled Glass...

The ability to add fillers are one key aspect of epoxy I really like. I have used milled glass to modify epoxy. Stuff I have is 1/32" cut and very fine, power like. Anything much larger would be considered chopped strand, not milled. The resulting mix is really strong, but what I don't like about the milled stuff is it tends to be very heavy. If you want a filler to beef up a joint, or to create a fillet, my recommendation is to use hollow glass bubbles and micro fibers. I use 3M bubbles and West Systems #403 fibers. The fibers are basically milled cotton. By volume, I'll mix about 1 part epoxy, 2 parts micro fiber and 2 or more parts bubbles. Depending upon how you mix, the viscosity is around that of mayo to peanut butter. This mix is strong, light and bonds well. Had very good luck with this mix and I like it a lot better than the milled glass. Add more or less of the fillers as per your application. Sometimes I'll use micro fibers as the only filler, other times when I mainly need a cosmetic fix, I'll mix only micro bubbles.

Cheapest source I've found for fillers is www.uscomposites.com. I've had good luck with all their products I've tried, including their labeled epoxies, and I believe their pricing is very reasonable. Only about $40 for a gallon of epoxy.

Cheers

Paul S.

JohnW, By the size of you aircraft, it looks like you just might price it by the gallon; to -get'r dunn. Nice craft.

So guy's I think, I hope, I got it; in reality, epoxy is actually overkill, med CA is quick and adequate for most well fitted/already prepped joints, but for firewalls, bulkhead joints, wing halves etc. the 30 epoxy is the better way to go both timewise and strength. Somebody mentioned CA can be used to pin an epoxy joint while it dries, and you can totally use CA or Epoxy from start to finish if you really wanted to. There's +'s and -"s with each but both seem great. You've really brought alot to the table explaining the chemical make-ups relevant to each too. This is a good thread, cause I just opened my TF 60 Corsair box and there's a whole bunch of glu-in ahead.

Paul

AQ500

I use 30 min epoxy on all high stress areas due to working at a hobby shop for over ten years. The amount of wreckage I saw over the years was astounding. I got to see what failed and figured how to make it so it won't fail. I saw a number of joint failures and most were caused by using fast curing epoxy or CA in high stress areas. You could see where the glue would just set up on the surface and the surface fibers gave way causing the failure. I never saw a glue failure where 30 minute epoxy was used. Usually if anything broke it was the wood just outside the joint where stresses were the highest.

Sure, most people will have success with any glue and can go for ever without any problems. I just don't take any chances after what I have seen.

elenasgrumpy

My Feedback: (4)

Give me 30 minute everytime. I need the extra working time to get it all right & where i want it. Being stronger in the end is a big plus too!

Paul S.

Yup, very good. I know I'm going to need more than normal time being my first so slower the better is for me.

Paul

RCKen

My Feedback: (9)

Planechucker,
Yep, it's real easy to feel "fumble fingered" when you are trying to put parts together when the clock is ticking on epoxy drying. What I do when I get ready to join parts like this is actually "rehearse" what I'm going to do. Put all your parts out and practice assembling them "dry" without using the epoxy. Do this until you feel comfortable with how you are going to assemble them, and you know exactly where all the parts go and how the go on. Once you do that then you're ready to actually mix your epoxy and glue your parts together.

Hope this helps

Ken

jaka

Hi!
I prefere Ca when glueing firewalls, both thin and medium.
I never use Epoxy for this!
Ca is much stronger!

Regards!
Jan K
Sweden

Paul S.

Ken yes it does help, I'm looking at the plans and the pieces here now and contemplating steps. I have one more question, CA is lighter? Say you fillet'd (read slobbered) all your seams with glue both sides, not just neatly tacking them, we're still talking just oz.'s from CA to Epoxy difference right?

Paul

ttolliver

My Feedback: (1)

Great discussion. I was first introduced to CA glues and epoxies with my first R/C airplane about 15 years ago and it's become a mainstay in my workshop. Lots of great advice here, but I feel compelled to make a comment to the newbies following this thread...

30 minute epoxy will occasionally surprise you and cure (start to gel) to the point where you're out of time in as little as 15 or 20 minutes, but I've never had it go quicker than that. The only reason I mention this is not to argue with others who have experienced the 5 minute cure, but to keep the newbies from being too afraid. Yes, definitely have a healthy respect for epoxy cure times. Know that heat accelerates the cure and be ready for it to suprise you, but don't break into a cold sweat over it.

One thing I haven't seen yet in the way of epoxy advice is anything about cleanup. Acetone (nasty stuff, I know) is the best chemical I've found to clean up epoxy off of fingers, tools, and such.

Tom