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Thread: advice for drilling for 3-inch waste

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  1. #1

    Default advice for drilling for 3-inch waste


    It didn't take me long to discover that I like self-feeding bits for drilling through studs and plates for my vent and drain lines. I have a medium duty 1/2" Dewalt right angle drill (DW120K, I couldn't justify buying a Hawg).

    What advice can you all offer me for drilling the hole to accomodate the 3-inch ABS (main drain and vent) that I am putting into my remodel? Hole saws seem to be too shallow to go through double plates...what does anybody recomend?

    Also, I'm using a 2 9/16ths for the 2-inch ABS and a 2 1/8th for the 1.5"

    What is correct hole size for the 3 inch?
    What about for for 4 inch?

    Thanks in advance,


  2. #2
    In the Trades Bob NH's Avatar
    Join Date
    Oct 2005
    New Hampshire


    3" and 4" Schedule 40 pipe ODs are 3.500 and 4.500 respectively. Add at least 1/16" for the hole saw.

    You may have trouble holding the drill for a self feeding bit in the size you are looking at for 3 and 4" pipe.

    The solution for the double plates is usually to clear the hole saw after each plate. If the wood gets stuck and stays in the hole instead of coming out with the hole saw, you may need to apply a chisel or put a screw in the piece to pull it out.

    I have found that a Roto-Zip with a 1/4" straight carbide bit does a great job where you may not have exactly the right size, or where you may not have clearance for drill access. Just handle it like a big Dremel tool, but with both hands. And hang on tight. I had one come out of my hands once and it fell and tore my pants where it came within a couple of inches of affecting my social life.

  3. #3
    Forum Admin, Expert Plumber Terry's Avatar
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    Aug 2004
    Bothell, Washington
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    You can drill for 3 and 4 inch pipes with a self feed bit, but don't feel bad if you just cut the plates instead with a sawzall or other type of tool.

    It's very hard to drill a large hole like a 3-9/16 or 4-9/16

    Even though I drill them quite well, most of the time it makes more sense to pull out the sawzall for them.
    Last edited by Terry; 01-19-2006 at 09:11 AM.

  4. #4
    DIY Senior Member finnegan's Avatar
    Join Date
    Aug 2005


    Go with the sawzall. You are going to have to use a nail plate either way. No one will see it after the wall goes up. For your vent roof penetrations, go with the hole saw. As suggested, if using the hole saw through plates, clear as you go. If you are doing work in old walls and encounter true 2x4s, the hole saw will not even go through one plate.

  5. #5


    Thanks! Yeah, these are 1916 "old school" 2x4s.

    So if I'm following what you are saying: I should cut out a 3 9/16ths section of the top plate (and hope that the siding and the sheetrock holds the exterior wall up!).

    This is definately going to be inspected...is a building inspector going to have any problems with that method from a structural standpoint? Do I need any *special* nailing plate for covering?

    Ahh. The secrets of the plumbers. I'm a carpenter and my top lip quivers like Elvis when I think of the damage a plumber with a Sawzall can do


  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    drill as deep as you can, remove, stick a screwdriver in the saw kerf, crack off the wood stub, repeat...
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7


    I just went through the same thing with my remodel. You can get 3 5/8" or 3 9/16" self feed bits on ****, but even there they go for $60-$80, so I gave up waiting for a good buy. I ended up with a Blu-Mol 4" hole saw from Home Depot for $17 ( I already had the arbor). I really like the Blu-Mol because they cut 1 7/8" deep and can easily go through 2" lumber.

    I also picked up the Harbor Freight version of the Hole hawg http://www.harborfreight.com/cpi/cta...emnumber=44790
    and it is fantastic. It is a nearly exact copy of the Milwaukee and I got it on a great sale for $59. I have really been using it for boring holes for the wiring and plumbing in the studs.



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