How would you cut cast iron pipe?

[KSever]

I have seen cast iron waste pipe cut before (with a sawzall) but it never came out smooth. I am planning in the future to replace a few sections and add in another drain pipe section to part of this cast iron pipe. I would appreciate any and all of your ideas on how to cut out a section smoothly without cracking the cast iron.

[LazyPup]

The preferred method is to use a cast iron snap cutter. Snap cutters are relatively expensive tools but they can usually be rented at a local tool rental company for a modest price. (Typically about $25 to $30 a day).

Cast iron is very rugged as a DWV pipe, but it is also brittle. In some situations it is just as easy to break out a section of the pipe back to an end hub, clean out the hub, then run your new pipe forward from the hub.

Before you begin cutting any cast iron pipes you must examine it thoroughly to insure it is adequately supported. Cast iron is extremely heavy and often it is installed in such a manner as to be self supporting. If you cut a section out their is a severe risk that all the pipe above the cut may come crashing down. IF you have any doubts whatsoever take the time to install additional blocking, strapping or other means to insure it will not fall down.

[Shelly]

Would a cutting grinder work?

[LazyPup]

There are numerous tools that will work such as a side grinder fitted with a cutoff wheel or a demolition saw, however in many cases the pipe will be too close to a wall or other obstruction to permit the required range of motion for the tool. The other consideration is that most abrasive cutoff tools will introduce a tremendious amount of vibration into the pipe during the cutting process which often results in cracking the pipe.

In the past I have cut cast iron using sawzall's and grinders but it is really a false economy. Cutting a 3" or 4" cast iron pipe with a sawzall will typically take about 20 minutes and consume 2 or 3 quality blades (about $2 each) or more per cut. The same is true of using grinders with cutoff wheels. When one considers the time involved and the cost of the Blades or cutoff wheels in my opinion you will be much further ahead to rent a cast iron snap cutter which can make the cut in a matter of moments.

The snap cutters are very easy to use. Basically it is a variation of a chain wrench. A chain similar to a bicycle chain is wrapped around the pipe at the point of the desired cut, then a handle is cranked, which tightens the chain until the pipe is snapped off clean. The whole process takes less than 2 minutes and leaves a nice clean end where you can then connect the new pipe by means of a Fernco or Mission coupling.

[thedcdude]

Lazy Pup

So when using the snap cutter, you don't have to rotate it (like a tubing cutter)? Just crank till the pipe snaps off?

[LazyPup]

You are correct, you do not rotate a cast iron snap cutter.

The snap cutter chain is wrapped around the pipe at the point of the desired cut then connected back to the cutter head in the same manner as attaching a chain wrench.

On the inside of the chain there are a series of small cutter points or teeth. As the chain is tightened by the crank the points create a series of stress points around the pipe. Cast iron is a very brittle metal and as the chain stress increases it will reach a point where you will hear a distinct snap. When you hear the snap remove the wrench and you will see a clean fracture line completely around the pipe.