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Old 03-05-2004, 09:43 PM
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Default Drilling holes in fiberglass

Any suggestions on how to drill into fiberglass. Doing an installation on top of livewell lid and looking for suggestions on right way to drill holes, without splintering.
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Old 03-05-2004, 09:45 PM
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Default RE: Drilling holes in fiberglass

Drill the hole ...easy pressure and then Champher the Hole ... that will prevent
gelcoat cracking !!...Do not buy Chit drill bit's ...John
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Old 03-05-2004, 10:51 PM
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Default RE: Drilling holes in fiberglass

Good question - I'm taking delivery of my new boat in a few weeks and this will be my first fiberglass boat (currently have aluminum) - I've nervous about drilling also - I thought I recall hearing on an old Shipshape TV episode that you should start a hole by first momentarily running the bit in reverse to break the gel coat - then forward. I thought this prevented chipping and splintering.
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Old 03-05-2004, 11:00 PM
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Default RE: Drilling holes in fiberglass

That reversing technique works great if you've got a hole saw. For a regular (small) drill bit like for a #10 or #12 screw you want to use light pressure and high speed. And the drill bit should be very sharp. Heat becomes a problem if you are going too slow or too deep, but you can use oil to help that. If you've got to cut a large hole, like for speakers, use a Dremel/Rotozip type tool rather than a jig saw -- it's much easier.
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Old 03-05-2004, 11:29 PM
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Default RE: Drilling holes in fiberglass

Drill a small pilot hole first. Then move up to a larger bit. And don't let the drill pull itself into the glass, this causes cracking. Take your time. Never thought about reversing the bit first, sounds like a good idea though.

Good Luck

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Old 03-06-2004, 12:58 AM
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Default RE: Drilling holes in fiberglass

If you're doing a lot of drilling and cutting 'glass, cover up. I was itching for a few days because of the glass fibers.

TCY
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Old 03-06-2004, 01:07 AM
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Default RE: Drilling holes in fiberglass

always drill through the gelcoat into the laminate. Dont drill out or it will fracture and chip nearly every time.
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Old 03-06-2004, 01:43 AM
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Default RE: Drilling holes in fiberglass

I like to start a hole in fiberglass/gel coat with a boring bit. I find the one cutting edge greatly reduces the chance of cracking or chipping of the gel coat. After bit is through the gel coat drill hole with regular drill bit. When using the boring bit, drill to the first size larger than the hole that is being drilled. This will give you a chamferd hole that is crack free.
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Old 03-06-2004, 06:50 AM
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Default RE: Drilling holes in fiberglass

In my experiance to get a clean hole, tape over where you are drilling, make your marks on the tape and drill with high speed and light pressure. I think drilling through the tape first helps get a clean entry into the gel coat. Masking or plastic tape have worked for me.
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Old 03-06-2004, 07:40 AM
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Default RE: Drilling holes in fiberglass

Depending on where you are drilling I would use epoxy to seal the hole after drilling to prevent any water from saturating into the wood core.
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Old 03-06-2004, 02:15 PM
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Default RE: Drilling holes in fiberglass

I do what abysmal said. Put down masking tape, then mark your spot on that. Finish drilling and then remove it. I also put down the tape first when cutting with the sabre saw or roto-zip. Use fine blades. Always chamfer the holes when you are done. If you cut a hole (like for a speaker) sand the edges smooth all the way around. Always make sure that you have drilled the correct size hole for the screw or bolt. If you use a power drill to put in a screw, don't force it. The screw will get hot, expand, and will likely break off in the hole. After making a dry run for fit, I like to put sealant on the threads of the screw. It not only helps the entry of the screw, once it dries it also helps keep the screw from backing out due to vibration or use (and of course, helps keep moisture out).

Good luck with the project. That's part of the fun of owning a boat.
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Old 03-06-2004, 02:36 PM
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Default RE: Drilling holes in fiberglass

Mike - The method that usually works for me ... I use my countersink first so that the width of my countersink hole is slightly wider than the drill bit I use to go through the fiberglass. When it's done you have a nice edge around the hole and no chips in the gelcoat. Good luck. Bob
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Old 03-06-2004, 08:00 PM
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Default RE: Drilling holes in fiberglass

first step cover the area completely with low adhearing tape"bluepainters tape" this stops most small spider cracks and if using a hole saw a quick reverse plunge then forward revs works good.
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Old 03-07-2004, 09:14 AM
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Default RE: Drilling holes in fiberglass

This works 100% everytime giving a clean slightly beveled edge on the hole. First decide whether clean holes in all fiberglass drilling from now & into the future is worth $25-$40 to you. If not, use the techniques above, if you want to make the investment then go & pick up a uni-bit. They have a really sharp edge and tend to shave the gelcoat larger & larger. The result is no chips and a very clean hole. Use the unibit to open a hole just larger than the final hole you want to punch, then switch to a standard drill bit and finish punching the hole. I've drilled more holes in fiberglass than I can remember & this technique has never failed me. I have drilled a couple holes in the wrong place, but did so with a very professional look to them.

examples are here:

http://www.toolking.com/shop/index2.asp?parent=336
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Old 03-07-2004, 12:11 PM
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Default RE: Drilling holes in fiberglass

KevinA, is that what you call a boring bit in your neck of the woods "uni-bit". Well with whatever name the bit is called, it is worth every penny the charge for good ones.

Using a standard twist bit can chip and or crack the gel coat. So there is little benifit in chamfering the hole after the damage has been done. Chamfer first then drill the hole.
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Old 03-07-2004, 05:38 PM
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Default RE: Drilling holes in fiberglass

garret,
I think unibit is a pretty common reference to this bit, but undoubtedly it has other names. Google seems to recognize the name.


One thing I didn't mention...if you pick up one of these, make sure it has a very fine point on it....very sharp to the touch when you tap your finger on it. Some of the bits have a ~45 degree angle point on them, look for sharper than this.
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