Cutting out the fiberglass arch for a bigger speaker - what rotary bit?

CougarCruiser

CougarCruiser

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Sep 28, 2007
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Seattle, WA
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(sold) 2004 420 Sedan Bridge
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I need to enlarge the speaker hole to complete my JL Audio speaker upgrade. I have a dewalt roto-zip style tool. I am wondering which bit is the best one to use?


I have the basic all around bit for wood and plastic similar to this:
http://www.amazon.com/Roto-SC4-8-In...8&qid=1426606131&sr=8-1&keywords=roto+zip+bit


Or, I can buy more of a grinding bit similar to this:
http://www.amazon.com/RotoZip-XB-TC...8&qid=1426606131&sr=8-8&keywords=roto+zip+bit


Or, is there a better option altogether? SpeakerHole.jpg
 
The first one is what I've always used (generally speaking, do unto fiberglass as you would do unto wood). The fiberglass is thin and it will cut very easily. Although I never quite remember till I start, it usually cuts better in direction than the other. Have someone hold a vacuum hose by your bit, especially if you're not adept at the way these cut. It's better to brace your hands against the tool and the glass at the same time.
 
Did this on my buddy's 320 we made a template from plywood clamped it to the arch and used a trim router. Came out great.


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I do have a rotary tool, I do not own a router... I'm pretty good with cutting drywall with the rotary tool, but am thinking fiberglass may be a different beast. I am going to give it a go though - and hope for the best!
 
You'll be fine. You've got a line already marked and, really, if you're a little off - it doesn't matter. No one is ever going to see it. The only reason your current hole is so nice is because it wasn't done by a person. There are times when various holes are done by a person from the factory - and they can sometimes be a little rough looking. It's like horseshoes - you just gotta get close. BUT... remember - you can always make the hole bigger - making it smaller again is not as easy.
 
I like the idea of making a template and using that if you want perfection. As long as you are close it will be ok. Speakers have a rather large flange.
 
I've never used a roto bit on fiberglass. Does he need to tape it off to avoid chipping?
 
I used the dremel version of a rotozip drywall "drill bit" looking bit to enlarge a stereo remote hole in a friends boat dashboard. The fiberglass was thicker than I thought. I would say to buy a couple bit because as it cuts the fiberglass it gets very hot and dulls down. Also +1 on having someone holding a shopvac hose next to the bit to suck away the fiber glass dust. I was itchy for a while after working that project. The vac and a mask, as well as a sacrificial long sleeve shirt are probably good options.
 
Had a friend use a jigsaw was great also, I would rely on doing it free hand take the time and make a template!


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I use roto yip tile cutting bits they are about 10.00 at home depot cut like warm butter.
 
Bucit said:
I've never used a roto bit on fiberglass. Does he need to tape it off to avoid chipping?
Click to expand...

Although I've used tape, there's other times I haven't. With the way the bit cuts, I'm not sure it's needed. But, certainly can't hurt. Take your time, don't force it.
 
I love using hole saws with that being said that looks like a big hole. the depot sells the circle cutter if you can glue a piece in the middle and try that route.

if you have a 4inch hole and you need to go to a 6 in hole. the trick is screw the 6in hole saw on to the drill. than screw the 4 in over it, the 4 inch will stay in the hole and act as a guide for the 6 inch saw
 
Tape the area you are cutting including a good ways out from the hole to protect t he gelcoat.

With a vacuum, you will barely control the mess, without the vacuum, you will have a freaking disaster on your hands. Wear a long sleeve shirt and tape the cuffs to your wrists with masking tape. Wear eye protection......

Never force or push a Roto-Zip. Let it cut at its own pace. The cutting bits are high carbon steel (or more) and are very brittle. Push them and you generate heat which dulls them quickly which makes you want to force them even harder. The bits are small so they break easily. That means flying metal at 10,000 rpm. Also, the bit is what holds the tool in the hole so you lose control of where the tool and remaining bit is going when you break off the end.

The potential for error, damage and injury is greater than with a jig saw, so I'd rethink the rotozip, but if you are careful, it will work.
 
Before you cut, make sure the arch is deep enough for the new speakers. Not all speakers are the same depth.
 
Maskin tape and jigsaw with fine narrow blade, is what I use in these applications. Narrow blade makes the turns easier. I usually tape the vacuum cleaner hose to the jigsaw (close to the surface), this way it follows the cuts constantly. I'd follow Frank's advice on eye ware.

Definitely check the depth to know whether spacers or something else will be needed.
 
Alex F said:
Definitely check the depth to know whether spacers or something else will be needed.
Click to expand...

as a possible alternative you may be able to use a spacer/adapter and not need to enlarge the holes at all if cutting the fiberglass is not something you are comfortable with...i have not personally used them but have heard of them...

cliff
 
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Alex F said:
Maskin tape and jigsaw with fine narrow blade, is what I use in these applications. Narrow blade makes the turns easier. I usually tape the vacuum cleaner hose to the jigsaw (close to the surface), this way it follows the cuts constantly. I'd follow Frank's advice on eye ware.

Definitely check the depth to know whether spacers or something else will be needed.
Click to expand...
+1 on use the jig saw much easier to handle also be careful on depth of jig saw blade buy a short blade.
I also like the router idea, faster cut and just as messy but you would have to make a template
 
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