Cutting a 3" cast iron pipe

I need to cut a 3" cast iron vent pipe to tie to a new PVC vent.
I am using a Milwaukee sawzall with a metal blade and it kept skidding and wouldn't start the cut at the right place. I then used a 4-1/2" angle grinder with a metal blade and cut a little notch and now I can engage with the sawzall without skidding.
However after 15 minutes of cut I don't think I am making a significant dent at all.
I used the same sawzall and cut through copper and EMT electrical conduits like knife through butter. But this CI pipe I am not making any progress.
I can't use the angle grinder there is simply not enough room around it.
I went to HD and they recommended a "grit iron" blade. Got that and it seems to cut a little bit, but again after 15 minutes, I am not even 10% through the pipe. The way I am going it would take 10 hours.
I remember seeing another blade named "ugly metal blade" I wonder if that would be better.
Is there a better way to do this?
I know a chain cutter may be used, but I want to avoid it. Part of the reason I am cutting this is because the lower section was cut by a plumber who used a chain cutter but created a vertical crack line and now I am trying to cut away all the damaged section.
Thanks,
MC
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all blades are not created equal, what brand of sazall blade are you using?
lubing blade with oil may help prevent blade dulling like it does with drilling in steel.
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In the metalworking/machining trade, cast iron is not THAT hard. It does, however produce no "chips" when being cut. Rather, it's a powdery residue that clogs saw teeth and drill flutes. I'd select a bi-metal (high speed steel teeth) sawzall blade with about 10 teeth per inch and use a lubricant such as kerosene to keep the teeth flushed out. Cast iron can be cut dry, but, again, keeping the saw teeth clear is important. I've had some success with candle wax at times, too. But it requires a helper to hold the candle next to the blade while it's sawing. Blasts of compressed air work, but everything within 10 feet is gonna be black. Your face included :)
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cutters would be best. If you have access all the way around the pipe a cut off wheel in a peanut grinder.
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damaged by using a chain cutter. I need to cut it the old fashion way instead of relying on it to break at the weak spot.
MC
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if snapcutter is out, try lennox diamond blade for sawsall.
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I found one at Lowes and bought it. That one did the trick and cut in about 10 minutes. Thanks!
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MiamiCuse wrote:

end, say less than about 4", you can use the method I used in a toilet pipe in a concrete floor. I needed to install an offset flange. I used a 2 1/2" cut off wheel in a 4" drill bit extender. I chucked the whole thing into a router. You can't run the router at full speed as slight unbalances will destroy the 4" extender. It could also be quite dangerous if it flied apart. I used a adjustable auto-transformer (Variac) to keep the speed slow. I worked from the inside of pipe from the open end and slowly but surely, cut through. I did have a nice flat spot to set the router faceplate while going around (the old flange). As I recall, it only took about 10 minutes.
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Interesting, I had to cut out some PVC pipe to replace a toilet flange and did the same thing using. I had started a bathroom remodel and wasnt having enough free time to finish the job so I hired a contractor. He told me he was going to have to charge me extra for demolishing the floor around the toilet flange so he could replace it. Once I rigged up a way of getting the cutoff blade deep enough in the hole it took less than a minute to do the job.
JImmie
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I think 'low to moderate pressure' bears repeating. It is instinctive to add pressure when things aren't cutting- but light pressure and pipe cutting oil are your friends.
Jim
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Get a weld cutting thin abrasive disc for the grinder. Done in seconds if you can get all the way around the pipe. Grit edge Sawzall blade will work fine, but slow. Regular steel cutting Sawzall blades won't work as you already know.
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Some pipe is just tougher than others. I have cut through many of them using a 6tpi Lennox blade that I buy at the plumbing supply store with no problems. Cutting a well baked vent stack in an attic this past summer I even broke down and bought a Lennox diamond dust blade which eventually cut through it. It was still a long process.
Keeping the blade lubed with a water mist from a spray bottle helped. It still took a long darn time.
Colbyt
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MiamiCuse wrote:

If all else fails, try:
* Thermite * Primacord
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Get a reciprocating blade desingen for cast iron!!

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gmail.com> wrote in message

some is tougher than others because it may have been recycled stell from something really tough.
scrap varies a lot depending on what the scrap came from.
cast engine blocks make tough drilling and cutting in their second life
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wrote:

Even more important than the content of the cast is the processing. Chilled cast is a REAL bugger to cur. Case is hard like glass
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