SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Feb 20, 2013, 11:32 AM
rip
ripacheco's Avatar
United States, FL, Niceville
Joined Jan 2013
1,655 Posts
Quote:
Originally Posted by Rodney View Post
If the container you mixed it in had a wax coating or finish, this would cause just such a problem. Be careful of what you mix the epoxy in.
I didnt' think about that... The plastic containers I used to mix the epoxy were from my wife's cake decorating class... maybe they had "something" on them that could have contaminated the Epoxy.

I am going to mix a new batch of that epoxy and let it dry by itself and make sure I dohn't get "rubber" after it cures.
ripacheco is online now Find More Posts by ripacheco
Reply With Quote
Sign up now
to remove ads between posts
Old Feb 20, 2013, 11:36 AM
rip
ripacheco's Avatar
United States, FL, Niceville
Joined Jan 2013
1,655 Posts
Quote:
Originally Posted by kenh3497 View Post
If the epoxy is still soft after you let it set, you can still save the wing. Carefully heat the joint with your heat gun and when it is nice and toasty warm VERY CAREFULLY start to pry the joint apart. Try a thin putty knife to start and work in in the joint. The heat will soften the epoxy to allow this to happen. Even well cured epoxy will respond to this treatment. Be patient though, as it does take some time.

Ken
I am going to try to "dislocate" my wing as you indicate. I'll make new ply wing joiners... i will try to clean as much as i can of the "bad epoxy" from my spars. (i can't sand it but i may be able to remove it with an xacto knfe)

Question though... will the "good" epoxy bond to the ruberized residue of the "bad epoxy" when I rejoin?
ripacheco is online now Find More Posts by ripacheco
Reply With Quote
Old Feb 20, 2013, 10:43 PM
KNS
Registered User
Switzerland, SO, Olten
Joined Dec 2012
363 Posts
Well, this would be something I would most certainly avoid.
Remove the crap completely. If this means having to make a new center-wingrib or the like then that's the way to go. Wing joints get much stronger if you pry/drill small holes in either side of the wing you are joining, then applying epoxy to both sides of the joint and then firmly joining pieces. Masking tape helps with excesss spillage and to fix the joint while curing.
Show a picture if you can, makes giving suggestions much easier.
Edit: don't drill holes in spars, of course!
KNS is online now Find More Posts by KNS
RCG Plus Member
Last edited by KNS; Feb 21, 2013 at 01:04 AM.
Reply With Quote
Old Feb 20, 2013, 11:05 PM
Registered User
New Bethlehem, Pa
Joined Nov 2006
824 Posts
If the epoxy is old, or if it is cold, I will nuke it in the microwave for 7 or 8 seconds, and it will flow like water. I use a piece of cardboard and place equal size portions (blobs) on the surface (I use my eye to gage them) and mix them with a toothpick. It hasn't failed me yet. For larger portions I mix them in a mixing cup with graduations. John
jbrooks01 is offline Find More Posts by jbrooks01
Reply With Quote
Old Feb 21, 2013, 12:10 PM
Registered User
United States, TX, Kerrville
Joined Oct 2003
2,273 Posts
Quote:
Originally Posted by ripacheco View Post
I am going to try to "dislocate" my wing as you indicate. I'll make new ply wing joiners... i will try to clean as much as i can of the "bad epoxy" from my spars. (i can't sand it but i may be able to remove it with an xacto knfe)

Question though... will the "good" epoxy bond to the ruberized residue of the "bad epoxy" when I rejoin?
That epoxy may still be working. I'd let it sit for at least a week. What's the rush?

CR
Charley38 is offline Find More Posts by Charley38
Reply With Quote
Old Feb 21, 2013, 12:19 PM
rip
ripacheco's Avatar
United States, FL, Niceville
Joined Jan 2013
1,655 Posts
Quote:
Originally Posted by Charley38 View Post
That epoxy may still be working. I'd let it sit for at least a week. What's the rush?

CR
You are right there is no rush. Just frustration. And a desire to find out what in the world I did wrong. Althought the evidence points to not mixing it enough.

I guess I can turn my attention to my power model that has been sitting there ignored while I finished the glider build.
ripacheco is online now Find More Posts by ripacheco
Reply With Quote
Old Feb 22, 2013, 12:52 PM
Registered User
Florida
Joined Aug 2004
4,135 Posts
It has been awhile since this post first appeared but; if it is still a problem sometimes just heating the bad area with a heat gun or storing in an area where you can get the ambient temperature up to about 160 to 180 degrees F for 24 hours or more, the old epoxy may set up harder.
Rodney is offline Find More Posts by Rodney
Reply With Quote
Old Feb 22, 2013, 12:58 PM
rip
ripacheco's Avatar
United States, FL, Niceville
Joined Jan 2013
1,655 Posts
Quote:
Originally Posted by Rodney View Post
It has been awhile since this post first appeared but; if it is still a problem sometimes just heating the bad area with a heat gun or storing in an area where you can get the ambient temperature up to about 160 to 180 degrees F for 24 hours or more, the old epoxy may set up harder.
I left the wing inside for almost a week now. It has hardened more. But if you press with your nail on a "blob" of epoxy on the joint you can feel the epoxy giving-in a little. I have the left over epoxy used on that joint and you can grab it folded as if it was hard rubber... (I heated this left over epoxy and let it cure for days.)

I remixed another batch and made sure i mixed it for a long time. I applied epoxy to a test-join... I let it cure overnight in the garage AVG temp 60F It did cure but the epoxy is not as "hard" as i'm used with other brands.

I think my wing will be ok. It is not going to break at the joint but I will NEVER be able to sand the epoxy around the joint. Its not hard enough.

I will try the heat gun as u mention. I remember reding "somwhere" that they used heat blankets over epoxied joints...
ripacheco is online now Find More Posts by ripacheco
Reply With Quote
Old Feb 24, 2013, 06:25 PM
Registered User
United States, TX, Kerrville
Joined Oct 2003
2,273 Posts
[QUOTE=ripacheco;24216781
I think my wing will be ok. It is not going to break at the joint but I will NEVER be able to sand the epoxy around the joint. Its not hard enough.

I will try the heat gun as u mention. I remember reding "somwhere" that they used heat blankets over epoxied joints...[/QUOTE]

Is there so much excess epoxy around the joint as to require sanding? If so, it may load the sandpaper rapidly but I'll bet you can sand it anyway.

Some epoxies will break down if enough heat is applied. I remember a ply firewall I had slip out of position after I left it all blocked up overnight. The epoxy was Devcon 30 minute. I was able to get it apart by blasting the joint with a heat gun, just short of scorching the balsa fuse sides. After that experience I pinned firewalls with hardwood dowels so they couldn't move!

I don't know if it's a good idea to try heat to that extent on a wing joint; that much heat might damage other glue joints.

FWIW,

CR

CR
Charley38 is offline Find More Posts by Charley38
Reply With Quote
Old Feb 25, 2013, 10:40 AM
rip
ripacheco's Avatar
United States, FL, Niceville
Joined Jan 2013
1,655 Posts
I will just leave my wing "as-is" after a week inside the house the epoxy is harder now. If i press hard with my nail I can still feel the epoxy "give" a little. But the joint seems very strong.
One thing is for sure. I will not use that kind of epoxy any more. Sig Epoxy and other epoxies sold by modeller companies are better. I have never had problems before.
Also the temperature 50-60s didn't help. I may use the "electric blanket" trick i read online.
ripacheco is online now Find More Posts by ripacheco
Reply With Quote
Old Feb 25, 2013, 04:51 PM
rip
ripacheco's Avatar
United States, FL, Niceville
Joined Jan 2013
1,655 Posts
Epoxy methods

And I thought I knew "everything" about Epoxy:

http://www.epoxymethods.com/faqs.htm
ripacheco is online now Find More Posts by ripacheco
Reply With Quote
Old Feb 26, 2013, 06:53 PM
20+ years of RC flying
BigIron357's Avatar
United States, FL
Joined Aug 2012
1,460 Posts
Okay, I just started my test of the Parbond #329. I squeezed out a small amount of each component spread equally next to each other on an index card. Then I mixed it like crazy for about a minute and a half. Stuck a test piece of 3/32 balsa onto the card and smeared it with epoxy then placed the ultralight fiberglass over the top and smeared a thin coat all over the wood, affixing it to the index card.

We'll see how it goes. Better be good because I'm ready to glass my wing center section! Temp in here right now is 77 indoors, 65 outdoors (windows are open) and the humidity inside is 52%.
BigIron357 is offline Find More Posts by BigIron357
Reply With Quote
Old Feb 26, 2013, 08:10 PM
20+ years of RC flying
BigIron357's Avatar
United States, FL
Joined Aug 2012
1,460 Posts
Well, it's been 90 minutes since I started the mix. The epoxy is still so soft that when I touch it lightly, my fingerprint shows. Not good.
BigIron357 is offline Find More Posts by BigIron357
Reply With Quote
Old Feb 26, 2013, 09:50 PM
20+ years of RC flying
BigIron357's Avatar
United States, FL
Joined Aug 2012
1,460 Posts
It cured!

Been 3 hours since mixing start but the epoxy is dry and hard. Still feels a little tiny bit sticky but is definitely kicked off and very strong already. Should be 100% cured by the morning.
BigIron357 is offline Find More Posts by BigIron357
Reply With Quote
Old Feb 27, 2013, 07:25 AM
20+ years of RC flying
BigIron357's Avatar
United States, FL
Joined Aug 2012
1,460 Posts
This morning my test bed is fully cured, completely dry and non-tacky and cannot be dented with a thumbnail. I guess I mixed it right this time.

However, it should definitely not be advertised as "30-minute" epoxy since it takes several hours or even overnight to cure.
BigIron357 is offline Find More Posts by BigIron357
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Question Epoxy for a Sky Raider Mach II trixieandme Balsa Builders 1 Jan 21, 2013 04:33 PM
Discussion Epoxy vs Hot Glue Gun cloud_9 Beginner Training Area (Aircraft-Electric) 24 Jan 16, 2013 05:50 AM
Discussion will fiberglass resin cure like epoxy? jeff262 Composites Fabrication 7 Jan 12, 2013 07:10 PM
Discussion 1/4scale FG/epoxy parts need a good home packardpursuit Giant Scale Airplanes 0 Jan 12, 2013 01:59 PM