Tips on Lots of Hole Sawing In Fiberglass?

Discussion in 'Fiberglass and Composite Boat Building' started by Jeff in Boston, Jan 10, 2022.

  1. Jeff in Boston
    Joined: Sep 2020
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    Location: Boston

    Jeff in Boston Junior Member

    I'll be making LOTS of backing plates and spacer plates as I redo the hardware on my conversion project (see thread in design forum). I figure I'll be cutting 50+ donuts out of fiberglass with a hole saw using a pretty heavy duty drill press. I'll be cutting 3/8" and 3/4" thick fiberglass / GPO sheet.

    Based upon what I've found in my google searches I want a small tooth bi-metal saw and want to run it fairly slowly. I have a Festool HEPA vacuum and will be hooking that up to make sure almost all the dust goes into the vacuum.

    Anyone have any other suggestions or tips?

  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Here is a link to Jeff's other thread (mentioned above) - if it is not referenced here, then nobody will be able to find it in a few years (or a few months even) if they come across this thread.
    Project Log - New Keel, Who Dis? (Pearson 26 to Electric Cruiser)

    That is very sensible re how you cutting all your backing and spacer plates out of solid fibreglass sheet.
    So many people would simply cut them out of timber, or plywood, and then face the very real risk of them rotting at some stage in the future.

    Just a thought - do these plates HAVE to be circular in shape?
    I am just thinking that if it is possible for them to be square or rectangular in shape, then you would have much less wastage of material (as they could all be next to each other), and it might be then easier to cut them out with a band saw (if you have one)?
    hoytedow likes this.
  3. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    This kind of job makes one appreciate giving some random guy on the internet money to waterjet cut them on his CNC.
    If you must DIY try a diamond grit wet hole saw made for tile. Water from the garden hose, clamp down the workpiece and have at it. For straight cuts wet tile saw or abrasive bandsaw.
    If you must cut dry, make a dust enclosure with a clear plastic face to attach the vacuum to, wear full suit and respirator.
    hoytedow and fallguy like this.
  4. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Get carbide tipped holes saws, they cut fast and last a long time, bi-metal blades won't last long at all.

    Or grit edge holes saws, they may not cut as fast, but do hang in there and take the abuse.
  5. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Fiberglass is super hard on tooling.

    Lotsa holes; use advanced tooling and run some water.
  6. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    This does sound like doing things the hard way, and the plates sound way too thick for anything on a 26'er except the keel bolts. The plate size is based on fastener diameter and on skin thickness. If the plate is just to provide a good land for the fastener and washer, the plate should be about 5/8 the diameter of the fastener. If the added plate is to be bonded to the existing skin or liner, go ahead and count that skin thickness.

    As a point of reference, the 50:1 Lewmar primary winches on my Catalina 38 are bolted to the fiberglass cockpit coaming which is about 1/8" fiberglass layup. Six 1/4" bolts hold the winches. I use 5/8" triple braid sheets that will hold 10,000 pounds. No backing plates, just washers - no problems after 40 years. This is a 600 square foot genoa and I can fly it in 20 knots on a 15,000 pound boat. Fiberglass is a lot stronger than you seem to think.
    bajansailor and hoytedow like this.
  7. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    actually, this is a realy great point

    Some of the backing plates might need to be larger as well. Cleats come to mind..
  8. Jeff in Boston
    Joined: Sep 2020
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    Location: Boston

    Jeff in Boston Junior Member

    Thanks folks! That gave me alot to think about.

    I need the 3/4 thick spacers because I plan to mount the outside stanchion base screws on the toe rail, and then use the 3/4" thick spacers between the base and the deck for the inside screws. But I will try cutting in water.

    I will look at other options instead of 3/8" thick backing plates for the inside. I'm looking at adhesive mounted nuts as I am working alone and I *really* want to minimize my time under the cockpit messing with hardware.
  9. Jeff in Boston
    Joined: Sep 2020
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    Location: Boston

    Jeff in Boston Junior Member

    Just did a test:

    Drill press at 250 rpm
    2” hole saw
    Cutting wood
    Wood submerged 1” deep in bucket of water.

    Cut clean, no splashing.

    Will try fiberglass next.
  10. comfisherman
    Joined: Apr 2009
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    Location: Alaska

    comfisherman Senior Member

    Having drilled way to many holes in lots of thick fiberglass while plumbing refrigeration systems in commercial boats, carbide go slow and have dust collection. Fiberglass is hard on tools, but that's part of why we love it. No special tips or tricks, it's just one of "those jobs".

  11. redreuben
    Joined: Jan 2009
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    Location: South Lake Western Australia

    redreuben redreuben

    Go to the ceramic tile section of your nearest big box store and get a diamond tipped holesaw the type used for cutting tap and plug holes in ceramic tiles, whizzes through FG no problem.
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