Originally Posted by
ericm979
The BB30 FM066 chinese carbon frame I just got has a full width aluminium bearing insert. I have seen pictures of BB30 frames with full aluminium inserts and with no aluminium insert, just a carbon shell. I haven't seen one with two small aluminium inserts. That would be more difficult to make and to make the inserts concentric, as you point out. They'd have to bond the inserts in and then bore the frame with the inserts.
The inside of the FM066's shell looks machined, not honed.
I would like to know if the frame is built up around the shell, with the shell held in place by the mold. Or if the frame is built up without the shell, then bored and the shell is inserted and glued in place. The latter would not allow the shell to be 'keyed' to the frame. The former would be easier to manufacture. The heat used to cure CF is too low to cause aluminium parts to warp. But expansion/contraction could be a problem for the built around the insert method.
I am pretty certain that the alloy insert be it BB30 or BSA sleeve is placed in the mold and carbon matrix is injection molded around the insert. This would be by far the most straight forward practice. What is unclear is how PF30 is created. I would say...a male core...possibly out of steel or aluminum is placed into the carbon mold and carbon formed around it...then drafted core is pulled. What is unclear is...is there a finish machining operation with PF30 which is basically a clean up of draft left by the core.
To your point about BB30 being a single alloy inserted sleeve...same as BSA sleeve...quite certain this is how most if not all BB30 frames are made...which makes sense...to control true position of left and right bore centers.
See Specalized BB30 pic below and compare to my BSA Roubaix above...pretty much identical...only difference being diameter of alloy insert...surrounding carbon frame members are the same geometry and size.