Originally Posted by Rogue Wave
...using a high reving edge cuttin rotatin tool can go very badly wrong if you don't use these tools regularly..
Well, the following comments are made recognising that all tools are potentially dangerous. However, judging by this thread and its predecessor, a good number of folk on here are not entirely comfortable or confident with tools.
General (very important) rule. To be in proper control of a tool you must not be forcing it.
Examples; use a big hammer softly rather than a small one forcibly, use a long spanner smoothly rather that a short one with all your strength, and, topically, use an angle grinder gently rather than pushing a god awful jigsaw to make it move forward!
I agree with Matt about circular hole cutters. These are cutting the whole way around their circumference and that is a bigger cut than any other tool I can think of.
Jig saws are awful things. By definition they are designed to cut curves, therefore cutting dead straight is difficult. The surface always needs protection because the foot invariably bruises it. It cuts by vertical movement which tears and chips in action. It is often used from the top side of a surface which means the damage it inflicts matters. They rarely cut freely so force it necessary.
On the other hand, an angle grinder wants to cut. It can be applied very gently allowing full control. It is also possible to rest one's hands on the workpiece to steady it. It runs straight once into the cut. The down side; you need dust, eye, ear and hand protection.
A router is a very dangerous tool. They are becoming common but they need great care. For one thing they're a gyroscope and they can fight you. And they can win.
General note about boat materials. Fibreglass responds to abrasion. Sanding, grinding, filing, rasping all work well. Tools with cutting teeth generally don't.
Rubbers, surprisingly, respond to abrasion also. Sanding and grinding work well. It can be sliced with a very sharp blade, eg. a Stanley Knife but it hates toothed cutting tools and drilling.
Back to the thread. When making holes in fibreglass, don't underestimate chain drilling. It's much quicker than might be imagined and complex shapes can be generated.
The tedium of drilling a series of holes seems daunting but it really isn't too bad. Buy the time you make your way to the shop for this special thingy, you can have the hole drilled and finished!
Finish the shape with a file. Buy half round files, they are much more use than a flat file. Better still, buy a selection.
The big plus, no special tools are necessary. It's dead cheap and it'll improve your hand skills. So you'll be able to cut up that non-sliced bread a lot straighter.