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  1. #1

    How to properly cut round duct (rigid)

    Hi,

    I was wondering how to properly cut round (rigid) ducts. I use the classic snips tool but I rarely get a decent cut and I always end up with sharp edges.

    Is there a tool available that can make perfect straight cut with smooth edges ?

    Any feedback would be appreciated.

    Mark

  2. #2
    Join Date
    Mar 2005
    Location
    Houston, Texas
    Posts
    11,864
    "They" sell a three jawed snip made for this. It could be Malco, I don't remember.

  3. #3
    Join Date
    Mar 2005
    Location
    Houston, Texas
    Posts
    11,864

  4. #4
    Join Date
    Sep 2002
    Location
    Northeast Ohio
    Posts
    4,842
    Depends on the pipe. Smooth lighter gauge galv cuts well with electric or manual double cuts as stated above. For pvc coated or galv spiral we use mini grinders with wizz wheels (metal cut off wheels)
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  5. #5
    Join Date
    Aug 2008
    Posts
    416

    Keep Forward Pressure on Snips

    If by sharp edges, you mean those nasty little burrs that make a needle look blunt, the key is to keep forward pressure when releasing and re-squeezing handle.

    When you release handle and cutting jaws open, you tend to "back" the jaws away from your last cut. So when you start to squeeze the handle you start your next cut a little ways back and create the sharp burr.

    So, after releasing grip and jaws open, push snips forward to make sure jaws opening is fully seated in last cut and then squeeze handle. After awhile it will become second nature.

  6. #6
    Join Date
    Apr 2009
    Location
    Texas
    Posts
    236
    I have the following:


    http://www.kett-tool.com/product_det...duct_model=KIT %23215

    The shear works pretty good for spiral pipe.

  7. #7
    Thank you the dangling wrangler and Heaterman for your help.

    The "Double Cut" pipe cutter is the tool I'm looking for.

    Heaterman: I want to cut 6" galvanized pipes.

    I was also told a simple hacksaw would do the job; well it will make straight cuts but will probably leave sharp edges.

    I found this tool online. This should do the job I assume:
    http://www.klenktools.com/Main/Produ...ew.asp#MA71500

  8. #8
    Join Date
    Mar 2005
    Location
    Houston, Texas
    Posts
    11,864
    If I've got a lot of pipe to cut, I use a cordless sawsall,with a metal blade. The cut isn't as bad as you'd think.
    If your gonna seal the joints with foil tape, be sure to use a rag, or wear gloves.

  9. #9
    Join Date
    Apr 2004
    Location
    Muskegon, Mi.
    Posts
    425

  10. #10
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,741

  11. #11
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,179

    Cool offset snips

    Wow! I'm really shocked no one mentioned offset snips yet. This is the std. in the hearth industry for cutting stove pipe: http://www.malcoproducts.com/products/snips/m2006.asp

    Note these are rated to cut 18ga. galv. but it gets tough at 22ga.. Fortunately, galv. vent connector is 26ga. up to 6" and should be 24 ga. from 6-10 then 22ga. for 10-16" diameter. These blow right through 30ga ducts.

    I wouldn't do a reline job without them--red for right circle/ green for left and bulldog snips for cutting drives.

    Another method involves using my Dewalt cordless minigrinder with metal cutoff wheels. It makes a dust cloud, sparks and stinks and you get a wicked burr but it is fast and I can usually cut pretty straight. Wear goggles--not just safety glasses and an N-95 respirator.

    Ditto on the fwd. pressure to prevent those nasty 'cat's whiskers'.

    To cut a hole in sheetmetal, take a crummy screwdriver or other piece of mild steel on an angle and whack it with a hammer to make a slice into the sheetmetal near the center of the circle or a few inches from a rectangle. I use a crummy Stanley 1" wood chisel because the tapered sides allow me to guide it in circles and it doubles as a scraper to remove caulk or duct pookie. Using the screwdriver, pry down to raise the metal up a bit so you can introduce the snips's foot below the metal then snip away. Hacks just use the screwdriver and hammer and leave out the snips part....

    When cutting snaplock pipe, make sure you engage the snips all the way into the jaws as you go to cut the lock joints as this is much tougher than the flat metal alone. When done, the female pocket will be pinched closed. Take the screwdriver and pry this open so the male end can fit in. Otherwise, your seam may pop open once heated. With the pipe lying down, take the male side and add an extra inward curl to it, which makes it easier to introduce into the pocket. It will straighten out once snapped together or you can round the pipe manually once snapped. Be sure to take pliers and clench the lock seam at the female end so it cannot come apart--I use long handled duckbill pliers from Sears for this.
    HTH,

  12. #12

    Thumbs up

    Thanks to everyone for your help.

    I think I will go with the double-cut snips. I will take my time to make a straight cut.

    Thanks again

  13. #13
    Join Date
    Dec 2007
    Location
    Cedar Grove, Wi-Sheboygan
    Posts
    1,582
    Easier to cut the rd. ducting before you snap it togeather, makes life alot easier.

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