What is the best way to cut holes in fiberglass to install speakers
6.5 and 10" subs

Jig saw works best unless you have a hole saw that big but that could be difficult to manage. Speaker holes are pretty low tolerance as they usually have a large flange to hide any inconsistencys

Or a roto zip. Love that damn tool

Roto-Zip or similar rotary cutting tool works great. I have a similar tool made by Ryobi.

Advice:
Buy and use the TILE bits for cutting fiberglass, as they are stronger than the wood bits. Ask me how I know that.
You have to go just fast enough that you don't start to burn/char the cutting material, but slow enough that you don't overheat the bit and break it. Ask me how I know that.
It helps to have three hands: two hands on the rotary tool, and a third (second person) right there with you holding the shop vacuum nozzle right behind your cut. Make sure you have the smallest filter on the shop vac, and this will save you a LOT of clean-up effort. Ask me how I know that.

Sydwayz, how do you know that? Seriously I agree I used one for the same thing & found out everything you did. They are pretty slick though.

yeah its a scary feeling when the roto bit snaps & u hear it flying around the cockpit. once you get a feel for the speed it works pretty well.

Have you guys tried the circle cutter attachement for the Rotozip or do you just freehand it? Nice tip about using the tile saw bits. I'm headed to Lowes!

Dan

I use one of these:
http://www.amazon.com/Milwaukee-2420...words=hackzall

with these blades:
http://www.amazon.com/Milwaukee-49-0...ackzall+blades

Works great and that little tool has a ton of uses.

Put some blue masking tape on the area to be cut regardless of the method will prevent scratches and help reduce chipping.

I lost my circle cutter attachment for years, and just found it the other day. I've never used it.

If you are cutting think fiberglass, perhaps with backer board or what-have-you; the bit will flex with the force of you moving forward on your cut. For this reason, I removed the collar guide on my particular tool so I could get the chuck holding the bit as close to the cutting surface as possible. Remember, it does not have to be perfect with speakers as you normally have a speaker bezel/cover that covers at least 3/8" beyond your cut. But check to be sure; and feel free to try the circle cutter, especially in thin fiberglass.

Also: wear goggles--not just safety glasses, but goggles. It's not only the bit you are worried about coming at you, but you want to keep that fiberglass dust out of your eyes too. A breather mask is a good idea as well.

I could be wrong but I think most of 6 1/2 speakers fit in a 5 1/4 hole. So I use a 5 1/4 hole saw.

http://www.amazon.com/MK-Morse-AV84-.../dp/B000E8BFHU