JonnyHK 

Dear All,

I know this has been discussed before, but for the life of me I can't find the correct key words to find it with a search.

What type of glues are best for bonding the alloy dropouts to the carbon seat and chain stays?

There isn't a lot of surface area there so I'd like to ensure I use the most suitable glue for bonding.

Any advice or help to find the old posts appreciated.

unterhausen

I think you just use a suitable epoxy. My understanding is you need to ensure that galvanic corrosion does not occur. Someone recently told me that epoxy is a good enough insulator, but some of the things I've seen at the bike shop make me wonder if that's true.

Dancingbear

3M DP420 is a good choice; although I don't know about it's availability in Hong Kong. Your surface prep is just as important.

Andrew R Stewart 

I'll just underline the OP's comment about the contact surface area amount need. A simple method of figuring out the contact surface needed might be to push the math of brazed drop out connections and the tensile strength of the filler used then compare to the strength of the intended glue/epoxy. Of course when in doubt do destructive testing of test pieces after doing so with brazed or bonded samples from known sources. But this step is too costly and/or time consuming for many from what I read often on these forums... Andy.

JohnDThompson 

At Trek we used a fiberglass sleeve to insulate between the carbon fiber and aluminum.

Canaboo

Nova lists epoxy choices on their site. 3M P 460 actually seems to give the best numbers from that brand. Loctite-Hysol and Araldite are also mentioned.
It might be hard to prep the surfaces depending on how much apart the pieces are.

taras0000

This. Don't just rely on the epoxy for insulation. Epoxies come in many formulations, some of which have filler reinforcements (kind of acts like re-bar within the plastic) which may alter it's conductive properties. A wrap or two of lightweight fiberglass is enough to insulate from galvanic corrosion.

JonnyHK 

Thanks all.

I'm guessing that the amount of bonding surface I have is OK since that is how it was supplied.

My easiest glue options (i.e. what I can get simply) are West System 105 or Techniglue CA. Obviously I'd need to thicken up the West System, but with both I'd have added chopped strands of fibreglass to thicken, strengthen, and also help with the galvanic problem. I do have some very light glass cloth, but not sure if there is room for that unless I am very careful or sand things back a bit.

I might also quickly investigate what other products I can get. The old discussions I was searching for did mention the strengths of various glue systems.

I can clean and prepare everything OK, but just had a feeling I should provide a bit more of a mechanical key as well. My thought was to use a tap to cut some small ridges on the alloy part (circular), possibly a diamond cut. Needed? A mistake?

Canaboo

Can you get West G-flex? That bonds tenaciously to Aluminum.You can us a hacksaw blade to rough the surface of the metal. You could wrap it with glass and form an elongated tang of glass that will bridge the alloy carbon junction with more total surface area.

JonnyHK 

I'll check.

taras0000

Look for adhesives specific to aluminum, or ones that are known to bond well. Aluminum tends to be trickier to bond with, unlike steel. Make sure that the surface is prepped really well to remove all of the oxide layer. You can add some "tooth" if you like, but it isn't necessary. Epoxy bonds on a level much smaller than what you can generate to make a mechanical interface.

Canaboo

G-flex was developed for repairing aluminum hulled boats. A toothing of a surface still increases total surface area plus it give the glass fibers a surface that they can interlock with. All of these little gains add up over the typical insert which isn't prepped much better than a glued in cork in a bottle.