Bonding a carbon seat-tube into steel sleeve

[Noize]

May one of you can help me out with this question..

In my current project I want to glue a Dedacciai carbon tube ( ID: 35,0 mm on bottom bracket side - 35,8mm at top) into a steel sleeve on the junction top-tube/seat-stays), similar to that what Nate Zukas is doing (see below)

I am curious how to do this in the way to ..

• make sure the sleeve on the top-tube junction is absolutely concruent with the sleeve on the bottom bracket. I cannot braze a seat-tube in and cut the unwanted part out. Because of the different diameters of the carbon-tube I have to use 2 different sleeves for that tube.
• how to get the glue into the sleeve without extracting it with the carbon-tube while pulling the tube through the sleeve and which gap in the diameters of sleeve and tube is preferably the best suitable for such bonding.

Thanks for the support, Ernst

[Andrew R Stewart]

Build the frame with a ST that can be cut away and the remaining ends can be shimmed per each end's needs. The "sacrificial" ST might not be from the bike world. It will be interesting to see what smart people suggest. Andy

[Noize]

Has one heard about a vacuum method to get the glue in ?
That would sound to be an alternative to tons of acetone required to clean the tube afterwards

[Mark Kelly]

The optimal bond line thickness will be called out in the data sheet of the adhesive. For the one I use (Huntsman 420AB) it is 0.1mm, that's a pretty typical value for high strength epoxies. The reason for this is that epoxy isn't very strong or stiff so you want a bond line thin enough for plastic constraint to apply.

Assuming your 35.8mm ID at the top of the tube is actually the OD, that calls for a sleeve with 36.0mm ID.

If your surfaces are correctly prepped and the two parts are round to less than 0.05mm and on exactly the same axis, getting the epoxy into the bond line isn't very difficult. If any of these conditions are not met don't even think about bonding the joint.

[shirk]

Firefly uses a segmented "dummy" tube between their lugs on the carbon/ti frames they make. Check out their IG feed to see it in use.

[Will Neide]

I use a dummy seat tube and just slide it out once I'm done brazing the frame.