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  1. #1
    Petty Officer 2nd Class watchinthebobber's Avatar
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    Question Drilling fiberglass with hole saw

    I need to drill a 1 1/8" hole in the fiberglass of my boat to install a plug receptacle. Can I accomplish this with a standard hole saw without problems? The fiberglass is about 1/4" thick. I've read about starting the hole with the drill in reverse to prevent the gel coat from chipping. Is that my only concern? Will the hole saw cleanly cut through the fiberglass otherwise?

    The instructions for the plug just say 1 1/8" hole saw, but I thought I'd ask before I butcher something.

    Thanks
    '94 Bayliner Capri 1850 4.3LX / Alpha One Gen II

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  2. #2
    Lieutenant Junior Grade marine4003's Avatar
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    Default Re: Drilling fiberglass with hole saw

    Yup..a hole saw is your best bet..if possible attach a piece of duct tape on the hull and mark your hole location on the tape..then drill,use a good quality NEW bit to minimize gelcoat damage.
    Nec aspera terrent

  3. #3
    Honorary Moderator Emeritus tashasdaddy's Avatar
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    Default Re: Drilling fiberglass with hole saw

    drill a small pilot hole first, then start the hole saw in reverse to score the gel coat, then go to forward and cut it.
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  4. #4
    Captain Tim Frank's Avatar
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    Default Re: Drilling fiberglass with hole saw

    Do you have access to both sides?

  5. #5
    Petty Officer 2nd Class watchinthebobber's Avatar
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    Default Re: Drilling fiberglass with hole saw

    Quote Originally Posted by Tim Frank View Post
    Do you have access to both sides?
    Not really. It's the inside edge of the bow. I can just barely reach my hand up there.
    '94 Bayliner Capri 1850 4.3LX / Alpha One Gen II

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  6. #6
    Captain Drowned Rat's Avatar
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    Default Re: Drilling fiberglass with hole saw

    Covering the cut area with tape is a good idea to prevent chipping. Use the blue painter's tape for a best result. Duct tape is a little gooey and will stick to the saw blade and make a mess on your hull.
    “We do not inherit the earth from our fathers, we are borrowing it from our children.”

  7. #7

    Default Re: Drilling fiberglass with hole saw

    i just drilled 2 holes with a holesaw in my fiberglass boat and had no problems.....i didn't know about the"backwards trick"....and i didn't have any chipping, but i would try it, wouldn't hurt.

  8. #8
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    Default Re: Drilling fiberglass with hole saw

    In addition to the good advice already given I'd like to add that the backside of the hole will end up a little rough. Can't be avoided unless you can get to the back side and partially cut thru.

    The other thing to know is to use a low speed and high pressure. High speeds and hole saws don't go good together. Use a dust mask, you'd be surprised at how much fiberglass dust it will create.

  9. #9
    Vice Admiral jay_merrill's Avatar
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    Default Re: Drilling fiberglass with hole saw

    I'll add another trick, If you ever have to enlarge a hole you will find it difficult, because there is no place for the pilot bit in the hole saw to drill into. Trying to place the large portion of the hole saw in the correct position, while engaging the drill won't work - you won't be able to keep it in place and will end up with a scarred boat, and a hole in the wrong place.

    Instead, clamp or firmly wedge a thin piece of wood (1/4" ply or similar) to the area to be drilled. Measure carefully to find the correct center point, and start the pilot bit in the wood. The bit will then keep the hole saw in place, resulting in an even hole, in the location that you want it.

  10. #10
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    Default Re: Drilling fiberglass with hole saw

    Quote Originally Posted by jay_merrill View Post
    I'll add another trick, If you ever have to enlarge a hole you will find it difficult, because there is no place for the pilot bit in the hole saw to drill into. Trying to place the large portion of the hole saw in the correct position, while engaging the drill won't work - you won't be able to keep it in place and will end up with a scarred boat, and a hole in the wrong place.

    Instead, clamp or firmly wedge a thin piece of wood (1/4" ply or similar) to the area to be drilled. Measure carefully to find the correct center point, and start the pilot bit in the wood. The bit will then keep the hole saw in place, resulting in an even hole, in the location that you want it.
    That's a pretty cool trick. It occurred to me, although I haven't tried it (yet) if you used a piece of plexiglass you'd be able to keep track of progress. Also less chance of messing up measuring.
    Why does a round pizza come in a square box?

  11. #11
    Honorary Moderator Emeritus tashasdaddy's Avatar
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    Default Re: Drilling fiberglass with hole saw

    plexi tend to melt, and gum up hole saw.
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  12. #12
    Lieutenant Commander Beefer's Avatar
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    Default Re: Drilling fiberglass with hole saw

    Quote Originally Posted by tashasdaddy View Post
    plexi tend to melt, and gum up hole saw.

  13. #13
    Petty Officer 2nd Class watchinthebobber's Avatar
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    Default Re: Drilling fiberglass with hole saw

    I just wanted to report that this install was a success. The hole saw worked beautifully! I didn't bother taping the spot. All I did was run the drill in reverse nice and slow to begin cutting the gelcoat. Worked great and no chips at all!

    I would like to post some pictures, but I've been way too busy.
    '94 Bayliner Capri 1850 4.3LX / Alpha One Gen II

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  14. #14
    Captain mthieme's Avatar
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    Default Re: Drilling fiberglass with hole saw

    Thanks for letting us know how it turned out.
    Glad it worked out for you.

    Nothing is so broken that Government can't make it worse.

  15. #15
    Vice Admiral jay_merrill's Avatar
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    Default Re: Drilling fiberglass with hole saw

    Quote Originally Posted by tashasdaddy View Post
    plexi tend to melt, and gum up hole saw.

    True, dat!

  16. #16
    Lieutenant Commander 109jb's Avatar
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    Default Re: Drilling fiberglass with hole saw

    You can use a hole saw on plexi without melting it if you know how to do it. You need to run very slow, clear the shavings periodically. You can also use a squirt bottle and cool the plexi and saw by spraying water on them.

    Most people run hole saws way too fast. By slowing them down and periodically clearing the shavings the hole saw will give better results and last longer too. You can burn up a hole saw in a matter of seconds on steel if you run it too fast.

  17. #17
    Seaman Fish~n~Chips's Avatar
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    Default Re: Drilling fiberglass with hole saw

    I think in general people use "all" drill bits improperly. Kinda like sand paper, works so much better when you do it right. Just my 0.02!

    ~Jason

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