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Old 28-01-2010, 18:07   #1
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Drilling Holes in Gelcoat

I've drilled lots of holes in fiberglass, but this time I really want to avoid chipping the gelcoat.

What tool minimizes the chipping ? I've heard of using a hole saw run at first in reverse, but this is a 1/2 inch hole, and I haven't seen a hole saw this small. I'll put a layer of masking tape on the surface, and test drill a smaller size bit first, but I'm open to suggestions. Would scoring the gelcoat with a spade bit help ? A Forstner bit ?

Or perhaps I should I drill a 7/16 hole and grind it out to 1/2.
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Old 28-01-2010, 18:15   #2
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carbon bit is what i say to use, the reason you get chips are from the teeth taking big bites as it drills. The finer the teeth the better.


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Old 28-01-2010, 18:20   #3
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Also start with the drill in reverse. It works with an ordinary bit as well as with a hole saw.
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Old 28-01-2010, 18:23   #4
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Step-bit, used by sheetmetal workers. Expensive, but comes in many size ranges
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Old 28-01-2010, 18:26   #5
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Step-bit, used by sheetmetal workers. Expensive, but comes in many size ranges
I had a similar idea, drill a smaller hole, with a piece of tape to minimize chipping, then work it out with a tapered reamer. I have an old hole punch kit I picked up years ago with a reamer that can go up to something like 3/4". The punches are pretty worn out, but I use the taper whenever I want to gently work up a hole.
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Old 28-01-2010, 18:28   #6
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You want a brad point bit or a 1/2" Forstner bit. They will not chip the gelcoat and you can still start both in reverse if you are still skeptical. I only use brad points or forstner bits on gelcoat...

Clean holes in gelcoat (ignore the Dremel bit, the holes were made with a brad point):



This is what they look like:
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Old 28-01-2010, 18:28   #7
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I've has good results with brad point drill bits up to 3/8. I've never tried a half inch one. You need to be careful on the back side as they will tear out if you don't have some backing, but I've never chipped the front side. Take it slow until your through the gelcoat. I see that they're available up to 1 inch on the internet. I got mine at Sears.
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Old 28-01-2010, 19:40   #8
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Thanks all ! Lots of options.
Maine Sail, I wondered about the forstner bit, but was concerned whether it would get dull too quickly cutting fiberglass rather than wood. What's your experience?
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Old 28-01-2010, 19:45   #9
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I have used a wood bore without any chipping
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Old 28-01-2010, 20:09   #10
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Thanks all ! Lots of options.
Maine Sail, I wondered about the forstner bit, but was concerned whether it would get dull too quickly cutting fiberglass rather than wood. What's your experience?
Mine are from Grizzly and are high speed steel. The kit I have is the H7956 and includes 31 bits (in the barn right now that's how I remembered the number). I think you can buy a smaller kits from Grizzly that are also HSS. I buy lots of my tools through Grizzly, great company with excellent value to quality ratio..
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Old 29-01-2010, 22:26   #11
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I use the tape method too - start with a smaller bit, and go from there directly to the right size with nothing more than a piece of tape and low drill RMS...
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