Bonding with epoxy:

Loading scenario: Ensure a sufficient adhesive is selected for the loading scenario. For example, 3M DP420 has an estimated shear strength of ~2,200 /sq. in. with common materials like aluminum and steel. When bonding to unique materials, such as HDPE, other adhesives may be better suited.

Proper fit: A bond-gap of ~0.005”-0.010” (per side) is recommended. This will ensure the proper amount of adhesive is used. Other adhesives may require a thinner, or thicker, bond gap. Consult the adhesive supplier for proper fit recommendations.

Bond Length: For ferrule tubing***, a good rule of thumb is a minimum bond length of 2-3x the inside diameter. For tubes <1” diameter, we recommend a 3” bond length as a default.

***our tubing is not ferrule tubing, I don't think

Galvanic Corrosion: Carbon fiber can cause galvanic corrosion on aluminum. If the aluminum is anodized, this should prevent corrosion since there is a layer of oxide between the carbon fiber and bare aluminum. The epoxy adhesive also can act as a layer to prevent corrosion. Another common way of preventing galvanic corrosion is to use a non-conductive outer (or inner) layer of fiberglass in the carbon fiber part to ensure the aluminum and carbon fiber do not come in contact.

For gluing the carbon fiber and aluminium, the 3M SCOTCH-WELD constructional glues are recommended. These are epoxy-type glues: (https://exelcomposites.com/guide-to-composites/fabrication-methods/gluing-of-carbon-fiber-composite-to-aluminum/)

Bond prep

Abrade: Using 120 grit sandpaper, or one of the other methods mentioned above, remove all gloss from the bond areas. This will increase the surface energy, thus increasing the strength of the bond.

Clean Surface: Wipe bond area with solvent. Gloves should be worn during all steps, so oils are not transferred to the bonding area. Allow solvent to evaporate (surface should look dull, gloss should to be removed). Can do a water bead test to verify sanding is adequate.

Bond: Apply adhesive liberally throughout both bond surfaces. 100% coverage will ensure a proper bond. When connecting the parts, adequate adhesive squeeze out should be observed.

Clean-up: After application, wipe away all excess epoxy. Use solvent to clean the non-bonded surface.

Fixture: Fixture or secure the bonded assembly to prevent movement while parts cure. As the epoxy cures, there is a possibility the bonded components will shift, affecting dimensions of the assembly.

Cure: Refer to the adhesive tech data sheet for the correct time, temp, and sometimes humidity cure process. Some epoxies require multiple days at room temp to cure properly. Do not handle the part until fully cured.

Information from: https://www.clearwatercomposites.com/resources/how-to-guides/bond-carbon-fiber-tubes/

Old information:

Noninvasive Connections:

https://www.mcmaster.com/structural-pipe-fittings/aluminum-slip-on-framing-and-fittings/

https://www.mcmaster.com/structural-tube-fittings/clamp-on-framing-and-fittings/

https://www.mcmaster.com/structural-tube-fittings/flush-fit-framing-and-fittings/

Not 100% sure what this is used for: http://www.xindawind.com/tube-clamp/57443569.html

Invasive (drilling, epoxy) Connections:

https://www.rockwestcomposites.com/shop/connector-accessories/carbonnect/carbonnect-system-components

We could also make our own connections pretty easily if we allow ourselves to drill

Materials to use to bond CF together: https://www.permabond.com/materials_bonded/how-to-bond-carbon-fiber-2/

There's a section on connecting CF with rivets instead of threaded fasteners. Overall this would result in less structural damage to the CF I assume: https://dragonplate.com/how-to-connect-carbon-fiber-tubes

The good, better and best way to drill CF: https://www.elevatedmaterials.com/drilling-carbon-fiber/

Bonding 2 tubes of CF (no drilling): http://www.carbonfibertubeshop.com/cut%20&%20bond.html

Youtube comment about drilling a CF Bike frame:

“No, don't drill a carbon bike frame. Carbon frames with through the frame cables have been specially constructed to have those holes and will be internally reinforced to deal with it.

But if you insist on doing it, then you'll have to buy a Dremel and use grinding tips to make the hole NOT DRILLS! A drill will almost certainly snatch forward at some point, creating a big risk that the material around the hole will split. If it does that, you may have to throw the frame away. But any hole you make without splitting the frame will need reinforcing and I recommend that you buy some carbon fibre "braided sleeve" https://www.easycomposites.co.uk/#!/fabric-and-reinforcement/carbon-fibre-reinforcement/carbon-fibre-braided-sleeve  to fit inside the hole and teflon tube in several smaller sizes https://www.ebay.co.uk/itm/PTFE-Tubing-Metric-3-15mm-OD-Sold-by-the-Metre-Air-Tube/331894146125?hash=item4d466ec44d:m:m0eLw1oKxdYHZPq29YhQOqg and some epoxy resin https://www.easycomposites.co.uk/#!/resin-gel-silicone-adhesive/epoxy-resin/EL2-epoxy-laminating-resin.html 

You will then have to wet out the carbon sleeve with a suitable sized teflon tube inside it, so that you can get it through the hole in the frame. Then you'll have to wiggle and circle the teflon tube about to try and spread out the carbon inside the frame, while also spreading out the carbon sleeve on the outside and smoothing it onto the surface. Then you'll need to leave a long piece of teflon, following the route you want the cable to go, in there till the epoxy sets. The teflon will hopefully not adhere too much to the epoxy and you should be able to remove it once set, then you'll have to do the same thing again, I suggest a minimum of three layers in all. When you do the final carbon sleeve, I suggest you'll need to leave your largest teflon tube in there full length, to help the cable go through.   And you'll need to consider sanding down the carbon sleeving on the outside as little as possible to retain as much strength as possible. So the end result may be kind of ugly.

So, that's what I'd do, if I was forced (at gun point) to make holes in my carbon bike frame.

Good luck.”

Comments

Nobody actually says how much a piece of CF is weakened when you drill holes into it - goes back to the knockdown factor from asha's interview. That being said, it would probably be wise to reinforce any holes we drill somehow. We can also try emailing other URC teams who have clearly drilled into their CF in their sar videos. It might be worth knowing if they've had any issues by drilling instead of clamping or epoxy. Anveshak for example just made aluminum gussets and bolted the CF to them, or at least that's what it looks like.