Hi!
First the typical question: What is a Chamfer? It is a angled cut usually at a Forty-Fove degree cut. Either to the inside(The area away from the detail. or Toward the detail, say on an inside exterior corner) There are some ways to do this and I believe My method has worked without a problem.
Once you have done your laminating of the paper part to the .005 or .1 mm Cardboard. Look carefully at your part. As Pawel said cut the piece rough. Then when cutting fine do this. Cut the edge at a precise Ninety Degree angle! Now are you ready? Here's the trick. Take your edge and apply Extra or regular fine C.A. Glue to it. Let it cure naturally(DO NOT Use Accelerator!) The Accelerator will discolor the printed colors on the part.
Once cured, then take the part and with an Emery Board or Nail Board..320 or finer sanding tool establish your Chamfered edge. The C.A. Makes a solid Hard surface on which to sand, thereby preventing the paper from getting a "Fuzzy Edge" and Also gives that edge some strength whel gluing it to another part. Ensuring clean edges.