Originally Posted by MichaelBaku

I'd take an earlier train from Aachen to Cologne to be on the safe side. I don't see any point buying a ticket from Aachen to FRA as most trains involve a change at Cologne anyway. If you're up for a bit of risk, take the 10 mins connection at Cologne but you only need a small delay (and it happens) for you to miss the connection. Better to give yourself more time and less stress/worry. A longer connection will maybe give you time to pop outside the station at Cologne and see the wonderful cathedral which is just outside the station or get yourself a coffee in one of the many outlets in the station.