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Cutting larger holes in GelCoat


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I have cut a LOT of holes in many boats and understand how to drill/cut the proper way to avoid spider cracking, etc....  However, my buddy bought some Exile 8" cabin speakers and needs me to install them.  Considering the biggest hole saw I can find is 6", what are others using for larger holes?  I'm not sure I'm a fan of a fine tooth jig saw since I cant reverse cut it and that might have the ripping effect.

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On ‎5‎/‎7‎/‎2018 at 2:58 PM, footndale said:

Maybe something like this in the correct size to at least the score the gel before using normal hole cutter?



that would be killer to use, but I could only imagine if that cordless drills went off 16th of an inch unleveled because it's by hand, then the thing could bite and rip of a section of gelcoat?



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1 hour ago, boardjnky4 said:

I’ve used a dremel in the past


no coffee (well 1 cup)? well rested? did your yoga that day?  well then break out the Dremel! I love that tool. I used it to open up the cutouts for the RF 8” to fit my JL 8” speakers. Freehand all the way. There were some sketchy moments  fiberglass would have been worse  

Another idea is make a jig out of plywood for a router guide and use a dremel router bit to cut out the FG. That should be tight. 

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Put a backing board in the hole, secure it (I can think of a few different ways), then use a Dremel "circle cutter". I've used a dremel circle cutter when making speaker cabinets (wood) but wouldn't be afraid to do the same thing with fiberglass. Make sure you get talc all over your exposed skin before you start cutting fiberglass, it helps keep the glass fibers from sticking to you and itching for days.


Edited by mikeo
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2 hours ago, robtr8 said:

Draw the circle you want.

Put an aggressive grit sanding sleeve on a drill drum.  https://www.harborfreight.com/4-piece-quick-change-sanding-drum-set-35455.html

Makes a hell of a mess but there's no way you screw up the gel coat.

I've done it this way.  be sure to rig up some method to control the dust.  I taped my shop vac hose to the back of the hole and had it running while I was sanding.  It worked fine.  Still messy but not insane.  Wear a resperator/dust mask because you'll be glad you did.

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