First question... is it a
vertical cast iron stack or a
horizontal cast iron stack?
If
cutting vertical stack then there are very special rules to cutting into these pipes because you need to worry about the
vertical load that is above the cut... if this is the case and you want to discuss vertical stack cutting post back and I will go into details. Can also click on this link and scroll down to post #3 for more information and
safety precautions:
https://www.askmehelpdesk.com/plumbi...om-252241.html
If this is what I suspect and connects into another question you posted (I also answered that post) then I am guessing that you want to know how to
cut into the horizontal cast iron pipe and then how to
transition from cast iron to PVC... am I close?
Like John said... there are a few ways to do this. For most homeowners I recommend using a sawzall and a carbide tipped sawzall blade (Lennox makes a great diamond sawzall blade but you probably can't find it)...
simply the safest way to go especially when you consider the fact that the next tool for this is famous for crushing some of the cast iron...
You can also rent a ratchet chain cutter (1st pic.) or a snap cutter (2nd pic.). These wrap around the pipe and you ratchet handle or twist knob to cut pipe. They usually work great but can crush the pipe or cause linear cracking of pipe which could cause issues back to the vertical stack... and you don't want to start messing with the vertical stack... so probably best to go sawzall and carbide blades.
To
transition from
cast iron pipe to pvc pipe you will need to purchase a
shielded clamp, commonly referred to as a mission or proflex shielded clamp... see picture. Any other clamp that you see at home depot is really illegal for what you are doing... ok? If going from 4" cast iron, then purchase a 4" cast iron x 4" pvc shielded mission clamp, then buy a 4"x3" flush bushing and install that into the pvc end of clamp. Pipe 3" to the toilet, 2" to shower, etc...
Let us know if need more information here...
MARK