So here is a frame I’m building for a customer that is primarily titanium but we’ve put in a carbon seatube and seatstays. These are tough to build for a few reasons. One is that you essentially have to build it twice. You have to make the frame and connector tubes as thought it’s whole and then you have to miter and fit the carbon tubes and bond them in. Another challenge is alignment. When you are building a frame that is missing tubes you don’t have the structure you typically depend on to maintain alignment. The last big challenge is bond line clearance. The space between the metal and the cabon in which the epoxy is used has to be exactly right to assure a strong bond. I’ve been mixing carbon into welded frames for about 10 years so I have lot’s of little tricks that keep me on track.