I am building a foam wing and tail feather airplane for aerial photography with a carbon fiber (CF) tube fuselage and CF braced landing gear. I was planning to tack the CF matrix together and then wrap each joint several times with Kevlar thread in such a way that the Kevlar would hold the CF in position. I would then soak the Kevlar reinforced joint with epoxy and have a substantial joint, probably stronger than the CF itself. I sanded the CF and used Hobby Town epoxy to tack the structure together. The structure falls apart with very little force.

The epoxy does not stick to the CF tubes. It's like I used a release agent. Then I scraped the epoxy off, cleaned the contact areas with alcohol and re-sanded the joints and tried CA glue. It would not hold the CF tubes together either. It's like the CF wouldn't allow the adhesives to stick.

Does anyone know what I'm doing wrong? This should work. I know people glue CF tubes together and I thought the strongest adhesive would be epoxy.

Attached is a photo of one of my joints and one of the broken joints.

Thanks,

Fred

use ca glue, carbon graphite loves it...

I've glued CF rods together with 5-min epoxy with no problem and just a little sanding on the rods. I would think CA would be too brittle but I haven't done it so I can't say for sure. You're right though, it should work the way you've tried... Silly question, but is your epoxy good (and did you mix it right?)

I bought the 5 minute epoxy a month or so ago and have used it several times. I like it because of the small nozzles that facilitate pouring out equal beads of each part. I have not destructive tested an epoxy joint on anything I've used it for. I have used it to glue some 1/8" oak scabs on two CF rods supporting a dihedral wing. Those joints have not broken yet, but they have not been involved in a "rough landing", yet. I guess I need to do a destructive test of my epoxy on some other material. I'll try it on some wood tonight.

I feel like this problem has something to do with the CF itself.

Thanks,

Fred

Every time I use epoxy on carbon fiber, I sand the area, wipe it down with rubbing alcohol and glue. Whenever I am removing the epoxy off the carbon fiber tubes, I have to scrap it off. Try sanding the area and cleaning off the residue, then wipe it with rubbing alcohol (91%), before gluing. I use 15 minute epoxy...

Challenger413

I bought some CF tubes for spars on a 1/4 scale project from a local kite shop need 6 to have enough length for the 4 spars as it comes too short. They sell a fiberglass ferule that slips into the joint and locks with CA. 3/8s tube the ferule is about 2" long, CA it 1/2 in one piece then slip the other over & CA it.
IFOs are built with CF rod, you bind it with kevlar thread and soak it with thin CA, works real good especially if you hit it with kicker.
I don't know if you could cut a scarf joint with a cutoff wheel, bind it and CA it or not, might be worth a try though.

It is very hard to find and pretty expensive but Loctite 404 CA iwill make a permanent bond to carbon fiber rod and Tubes
I used to work as an Archery Technician for High Country Archery out of Dunlap TN and we used to have problems with keeping the aluminum inserts from pulling out of the ends of the carbon arrows until we came across this loctite 404 Cyanoacrylate adhesive .
Also, as C43 said you will want to sand the area that will be bonded, I would go a step further by cleaning the sanded material with alcohol.
There is an outer oily film on carbon which is a waxy residual release agent used in the tube manufacturing process that keeps pretty much anything from sticking very well to the carbon material.
Also, if you plan to paint the rod you may as well go ahead and sand the whole rod in order to get the paint to stick.

EDIT: OH I almost forgot JB Weld works excellently for bonding carbon tube together as well but has a longer cure time than CA like 24 hours but works better than CA. one other method and probably the best method would be to tack together the parts with CA then wrap them with thin strips of carbon fiber mat then applying polymer epoxy resin, AKA Fiber glass resin.
you will still need to sand and clean the tubes regardlessof which method you decide to use.

what kind of ca glue are you using? i just did some gluing to CF today and my 5 min epoxy didn't stick. then after that i cleaned it up and tryed odorless ca. and it broke off because i didn't clean it good enough. the third time i used a regular old super glue with my kicker and it did the trick! thin super glue is so much easyer to use.

I've had luck with doing a wrap of fibrous thread wrapped around a tack bonded connection. Then soak the thread with thin CA and let it air cure or super light misting. This has been rock solid for me.

I've even used this to mount hacker cross style mounts to firewalls and had no problems with the motor ripping out (on an A30 mind you!).

Warydragon, Try high temp hot melt. It will hold almost anything and is slightly flexible. You may be surprised (and delighted)!

Originally Posted by warydragon

I am building a foam wing and tail feather airplane for aerial photography with a carbon fiber (CF) tube fuselage and CF braced landing gear. I was planning to tack the CF matrix together and then wrap each joint several times with Kevlar thread in such a way that the Kevlar would hold the CF in position. I would then soak the Kevlar reinforced joint with epoxy and have a substantial joint, probably stronger than the CF itself. I sanded the CF and used Hobby Town epoxy to tack the structure together. The structure falls apart with very little force.

The epoxy does not stick to the CF tubes. It's like I used a release agent. Then I scraped the epoxy off, cleaned the contact areas with alcohol and re-sanded the joints and tried CA glue. It would not hold the CF tubes together either. It's like the CF wouldn't allow the adhesives to stick.

Does anyone know what I'm doing wrong? This should work. I know people glue CF tubes together and I thought the strongest adhesive would be epoxy.

Attached is a photo of one of my joints and one of the broken joints.

Thanks,

Fred

Last night I re-sanded my CF parts and applied another epoxy, Scotch Weld 2216 to the joints. It took overnight to cure and seems to be holding today. I'll clean and re-sand the rest of the CF structure today and tack the joints with the Scotch Weld 2216.

I guess I wasn't sanding and cleaning the joints enough to remove all of the release agent from the carbon fiber tubes.

I may use hot glue the next time.

Thanks for the advise,

I'll let you know how it turned out.

Fred

Hot glue, CA, and 5 min epoxy do not work well for CF. If you need good adhesion and strength slow set epoxy and PU (Gorilla/Sumo) are the best choice.

Hello RogueTitan,

do you mean this one : https://i.ebayimg.com/images/g/VHYAA...nSX/s-l500.jpg ?

Best regards,

Originally Posted by RogueTitan

It is very hard to find and pretty expensive but Loctite 404 CA iwill make a permanent bond to carbon fiber rod and Tubes
I used to work as an Archery Technician for High Country Archery out of Dunlap TN and we used to have problems with keeping the aluminum inserts from pulling out of the ends of the carbon arrows until we came across this loctite 404 Cyanoacrylate adhesive .
Also, as C43 said you will want to sand the area that will be bonded, I would go a step further by cleaning the sanded material with alcohol.
There is an outer oily film on carbon which is a waxy residual release agent used in the tube manufacturing process that keeps pretty much anything from sticking very well to the carbon material.
Also, if you plan to paint the rod you may as well go ahead and sand the whole rod in order to get the paint to stick.

EDIT: OH I almost forgot JB Weld works excellently for bonding carbon tube together as well but has a longer cure time than CA like 24 hours but works better than CA. one other method and probably the best method would be to tack together the parts with CA then wrap them with thin strips of carbon fiber mat then applying polymer epoxy resin, AKA Fiber glass resin.
you will still need to sand and clean the tubes regardlessof which method you decide to use.

Another good thing to use is the type of epoxy designed for plastic repair. It generally sticks better and has some kind of plastisizer/flex agent so it doesn’t get brittle like regular epoxy and withstands shocks better due to having a little give.

Instead of butting it, drill a hole in the larger tube, insert the smaller one and put a drop of thin CA on it. Done. Epoxy will work too with proper surface prep.