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Old 09-01-2010, 00:21   #1
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Drilling into Gelcoat Successfully

I have to drill some small (1/8" ) holes into FRP through gelcoat. How can I keep the surrounding gelcoat from splintering/cracking? Thanks
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Old 09-01-2010, 05:12   #2
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Try this, asuming you start from the frp side, put some blue scocht tape in the gelcoat side and use first a small pilot drill bit to make the pilot hole, and use the right drill bit to make the next size hole, use a sharp bit and be sure the bit dont be out of balance in the drill machine, or after the pilot hole is made it , Best regards.
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Old 09-01-2010, 07:04   #3
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If you drill a hole with a sharp 1/8" drill bit you won't have trouble. The trouble starts when you drive a screw into the hole. To solve that, counter sink the hole after drilling it so that the threads of the screw don't touch the gelcoat when you drive it in. Put a little 3M 101 or Boatlife Lifecaulk into the counter sink cavity before driving the screw in.

When you use bolts, follow the same procedure so that the bolt can never put any pressure on the gelcoat.

If you get cracks while drilling, buy better drill bits. I use cobalt bits for stainless steel which works great in gelcoat. Check the bit with your fingers to see if it's still sharp. That is easy to learn when you can compare with a new bit of the same size.

cheers,
Nick.
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Old 09-01-2010, 07:51   #4
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All of the above plus use 4 piont bits if you can find them.
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Old 09-01-2010, 08:59   #5
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Also, go with a light pressure when drilling the gelcoat itself.
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Old 09-01-2010, 09:37   #6
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Use a reversing drill and before you actually drill the hole run the drill in reverse to get the drill bit to 'burn' through the gelcoat and not cut or split it, then drill through the rest of the fiberglass.

If you intend to put a screw into the hole, or tap it with a thread, then use a phillips or pozidrive bit in a drill or electric screwdriver to countersink the hole and snooth out and seal any fine cracks that may have occurred during the drilling and prevent splitting the gelcoat when the screw is installed. Works every time
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Old 09-01-2010, 10:27   #7
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center drills

I have found having a set of center drills invaluable for a lot of things, including not chipping gel coat.... Suggest 1/4, 5/16, and 3/8.
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Old 09-01-2010, 13:12   #8
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Drilling Gelcoat

Good question! I have found that using drill bits made for cutting Plastic sheet (Lexan etc) works well. You can buy them or make your own if you have a bench grinder or for small bits a dremmel tool.

The "web" of the drill must be thined down as much as possible and the angle of the bitting surface should be steeper than a regular drill ... about 70 Deg. ( A deeper V not a shallow one) Then the two cutting surfaces should be flattened Much like a paddle type bit so the edge that cuts is more like a scraper. This way the cutting edge does not cut like a chisel. I will try to post a picture.
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Old 09-01-2010, 13:26   #9
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BTW, the scotch tape idea is often mentioned, I found it never works as the forces involved are too grat for the tape to hold. Good sharp drill bits will not cause any cracking. Most of the cracking comes with pressure from the screws or bolts.
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Old 09-01-2010, 14:22   #10
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Although it might not stop cracking, the masking tape is still a good idea if the cosmetic finish of your gel coat is important. It will help stop the drilling/cutting shrapnel from scratching and generally messing up the remaining gel coat. This is especially the case when cutting larger holes with a hole saw or cutting irregular shapes. And it makes measuring and marking out the shapes really easy!
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Old 10-01-2010, 02:12   #11
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thanks everyone. we are currently in Cape Town and will hopefully start sailing our new catamaran back to the Caribbean by the end of next week.
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Old 10-01-2010, 06:23   #12
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You might find this link useful for a number of projects. Compass Marine Project Articles Photo Gallery by Compass Marine at pbase.com
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