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Old 03-08-2012, 05:57 PM   #1
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Default Enlarge cut out?

Want to replace my 6 1/2" speakers with some 8" but of course my cut out isn't large enough. How do you pro guys enlarge a cut out? Is a hand guided jig saw the only choice? Sure wish I could figure a way to use a large hole saw but with no center in place to start a pilot hole it seems like a no-go....
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Old 03-08-2012, 06:04 PM   #2
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I cut almost all of my holes on the boat with a Roto Zip. Works very well in tight areas. Just trace your opening and follow the line. Once you have the opening close, buy a 1" flap sander (about $2.50) that fits in your collit and use it to clean up your opening for a perfect fit.
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Old 03-08-2012, 06:13 PM   #3
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You. Da. Man. Thanks for the hint!
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Old 03-08-2012, 09:04 PM   #4
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You can put a temp patch panel over the existing hole and use a hole saw. You can screw the patch into the part of the panel that will get cut out with the larger hole.
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Old 03-09-2012, 03:46 AM   #5
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Put two hole saws on the same bit. The one that fits the existing hole will be the guide. Be careful. An 8" hole saw can get away from you. Use a low power drill just in case it gets caught! Drill in reverse.
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Old 03-09-2012, 05:50 AM   #6
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I recently did the identical upgrade and used a RotoZip. I used blue masking tape around the hole, traced the template and then used the fiberglass bit on the Rotozip which cut it without issue. I also cut a hole for a 10" sub. Cleaning up the fiberglass dust was a pain but otherwise the project went really fast.
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Old 03-09-2012, 06:02 AM   #7
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Cut yourself a 9" x 2" strip of wood. Insert it into the hole and screw the wood in place through two opposite existing speaker screw holes. Find the center of the hole and mark the wood. You now have a guide for your hole saw! The hole saw is going to give you the best result, but be carefull those big ones have a mind of their own some times!
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Old 03-09-2012, 06:45 AM   #8
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I also need to enlarge a hole for a new GPS unit. Will my Dremel oscillating tool do the job?
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Old 03-09-2012, 06:59 AM   #9
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Quote:
Originally Posted by Mellow Yellow View Post
I also need to enlarge a hole for a new GPS unit. Will my Dremel oscillating tool do the job?
It could, but if you have access to a jig-saw and room to manipulate it on the console, that with the right blade is probably a better tool as it is easier to control and get clean straight cuts than the Dremel/RotoZip type tool.... at least it is for me.....
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Old 03-09-2012, 05:17 PM   #10
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The hole saw ideas are the best, but how much i$ an 8" hole saw? Tough to purchase locally as well and for a one time use?
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Old 03-09-2012, 05:32 PM   #11
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I used a dremel with a new cutting bit to cut a 10" hole in solid glass for my sub. Take your time and let the tool do the work, don't try to move it faster than it wants to cut. I got great results.

BTW, does anyone else like the smell of cut fiberglass?

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Old 03-09-2012, 05:56 PM   #12
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BTW, does anyone else like the smell of cut fiberglass? ]
I'll be reminded if I do or don't tomorrow......
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Old 03-09-2012, 06:12 PM   #13
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A jig saw is a very handy tool and could be used for this cut.
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Old 03-09-2012, 06:13 PM   #14
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Shit is toxic watch out if youre ever grinding large areas
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Old 03-09-2012, 06:38 PM   #15
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I would use a saber saw to enlarge a speaker hole. I have a rotozip, but I don't think it's very controllable cutting dense materials. You might be ok if you use a circle cutting jig-which I have used for about 20 recessed light holes in my house's ceilings. Depending on the material you might want a carbide bit on the saber saw. For rectangular holes, I pull out the oscillating cutter-I have a dremel and a rockwell with carbide cutters
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Old 03-09-2012, 06:41 PM   #16
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Hole saw, make your own guide, piece of cake.
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Old 03-09-2012, 07:27 PM   #17
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Umm, have any of you guys priced an 8" hole saw lately? http://www.customholesaw.com/index.p...e19f478cfa01af
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Old 03-09-2012, 07:30 PM   #18
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Haha, maybe if you buy from a site called customholesaw. Go down to your local plumbing supply place and pick one up for $30. I have sizes up to 12"....all bought at my local plumbing supply. Don't think I've ever paid more than $50 for one. And I live on and island where everything is more expensive.
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Old 03-10-2012, 04:18 PM   #19
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Quote:
Originally Posted by wingless View Post
A jig saw is a very handy tool and could be used for this cut.
I had to enlarge mine to go from 5 1/4" speakers to 6" so I was basically just trimming the hole. I started out trying to use a roto-tool, but found a hand jig saw easier to control. I also didn't center the new hole over the old one. I shifted the new hole so that the bottom edge of the old and new were matched. I was cutting through about 7/8" of fiberglass and wood, otherwise I think the roto-tool would have worked had it been much thinner. I also used tape to protect the gel coat from the foot of the saw as I was cutting.

Last edited by kunzman; 03-10-2012 at 05:29 PM.
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Old 03-10-2012, 06:19 PM   #20
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Went to buy a Rotozip but ended up buying a Dremel 4000. Rotozip seemed pretty big for my long term projects after this is done. Dremel did fine on the two front speaker holes on the forward side walls of my center console. About 3/8" fiberglass I guess, maybe a little thicker. No problem controlling it and it cut well but went through 1 bit per hole though. Then I tried the two on the console under the stearing. Didn't count on it being 3/8" glass over 3/4" plywood. Had to do those with a jig saw. Despite my taping it still did a little damage to my gelcoat so will have to buff and fill a few places with some gelcoat repair.
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