i also want to know do you superglue the headpins in the polymer clay before you bake it
Superglue after baking You can just bake polymer clay in a glass dish - like pyrexI wouldn't use wax paper or aluminum foil, not necessary.
Can I suggest the obvious answer - that you are pulling the yarn too tight? Thousands if not millions of people around the world manage to make up their loomsIf you don't get an answer here (and I don't think you will) talk to the places you buy yarn (or their competitors) and get in touch with other people who are weavingThe acrylic knitting yarn my wife uses is so strong that I would bet about 10 strands would hold my considerable weight and I certainly couldn't pull a strand apart with my bare hands without damaging my hands.