32 years of experience has taught me to use a few tricks when it comes to repairing plumbing problems. A reciprocating saw and a few metal cutting blades will cut your cast iron pipe and then you can attach your fernco coupling and you are all set to run your plastic pipe. When cutting castiron pipe it is best to buy blades that are better in quality as cast is very hard. I prefer Lennox blades with 18 teeth per inch and the gold brand if possible. You can try a set of cast iron cutters, but you are taking the chance of the cast cracking or crushing if it is old. Recipprocating saw works best for me. good luck...Please subscribe and have a great day.