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Thread: how to cut 7" ducting?

  1. #1
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    how to cut 7" ducting?

    I am starting to place the ducting away from the cyclone. I am using Nordfab 7" for the main lines. Almost immediately I have the need for a piece shorter than the standard 60" length. I can make this by cutting a 60" pipe and using an adjustable nipple.

    My question is what is the best way to cut this 7" diameter pipe? I do not have access to a metal cutting bandsaw and the future need to cut pipes will arise at unpredictable times, so I would rather not take each piece as the need arises to a shop with a metal bandsaw. I have a standard 12" hand hacksaw, but I won't have much stroke after I subtract the 7" pipe from the 12" blade, nor do I have a really good way of holding the pipe while cutting. My other obvious choice is a handheld electric jigsaw with a hacksaw blade. A little worried again about control and getting the cut started. Also I have a reciprocating demolition saw that can be fitted with a long hacksaw blade.

    Any suggestions on how to do this? I am hoping a missed an obvious home remedy.

    James

  2. #2
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    I use tin snips to cut my ducting. Is the Nordfab too thick for this low-tech method?

  3. #3
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    Quote Originally Posted by Todd Burch View Post
    I use tin snips to cut my ducting. Is the Nordfab too thick for this low-tech method?
    I am not sure. I think it is 22 gauge. Also not sure how I would start the cut since each end is rolled for the clamping. Ideally one cut pipe would give me 2 adjustable length pieces if I do not damage either rolled end.

  4. #4
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    I would use an angle grinder with a 6" cut off wheel/disc. Mark the line with a sharpie and cut it. It is actually pretty easy to maintain good control for a nice quality cut.
    Brian E. Cosgrove

  5. #5
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    I am a retired sheet metal worker so I would just cut it with tin snips. You might want to get a pair of "double cut " electric shears. I think Harbor Freight has them, fairly cheap. Either way you start the cut by drilling a hole ( about 3/8") and cut from there all around the pipe.
    No PHD, but I have a DD 214

  6. #6
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    I'll second the side cutter with a cut off wheel if you have one. Then I removed the burr with another 4" side grinder with a grinding wheel. I did mine with a old 4" grinder and it worked great + it's nice and light to hold and control.
    Last edited by keith denbesten; 10-10-2012 at 8:24 PM.

  7. #7
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    Angle grinder with a cut-off disc, definitely. If you don't have a grinder, you can get one from Harbor Freight for about $15.

    Forget about snips. You aren't getting through this stuff with snips. Any kind of blade will have to have super fine teeth to avoid being really grabby and dangerous, and therefore it will be slow. A plasma cutter would probably do great if you have one.

  8. #8
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    And to draw a straight line around it, wrap a piece of newspaper around it - line up the edges - and mark with felt marker pen....
    Funny, I don't remember being absent minded...

  9. #9
    I usually just take a sharpie and measure from the square end and put a mark every so often, then start the cut with a hand hack saw, then use a jig saw with metal cutting blade to saw the piece the rest of the way around. I have a bench with a vise on the end, and put the pipe in the opening to hold it.

  10. #10
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    I just used a jig saw with a metal cutting blade. Piece of cake!
    Last edited by Philip Rodriquez; 10-11-2012 at 10:12 AM. Reason: typo

  11. #11
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    I start the cut with a very thin cutoff wheel on my angle grinder (you could probably use a dremel with a cutoff wheel) to get a starting hole then go around the pipe with a very fine metal cutting blade in my jigsaw. Less sparks and stink in my wood shop that way. I found it difficult to get a nice even cut with just the grinder due to all the sparks messing with the sharpie line. Then debur with a rubber cratex wheel in my grinder. I hold the pipe in my woodworkers vise that opens to at least 7". And congrats for going with steel duct. To me, a DC system with steel duct vs PVC pipe is like using hardwood vs MDF on furniture. But that is just me.

  12. Quote Originally Posted by Brian Cosgrove View Post
    I would use an angle grinder with a 6" cut off wheel/disc. Mark the line with a sharpie and cut it. It is actually pretty easy to maintain good control for a nice quality cut.
    I did my whole shop like this (used a 4" grinder instead). Worked perfectly, cleaned up the inside edges with a fine rat tail file and the outside edge with a fine flat file.

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