Thanks for any help appreciate any help.
Dremel is a company. Did you just want a tool from them, or were you referring to a roto tool in general?
The best is again preference. Did you want a small light weight tool or a more industrial tool? Most say they want one with slower RPM/s not a high rate of speed for plastics. I like the tools that hang up on a stand with a long flexible shaft. The top of the line have a foot pedal to control the speed as you work.
. The smaller the tool, the less torque at low speeds so you get high rpm’s to get the job done. If the motor is larger, it has more torque and can do what ever you need at low speed.
I would not use any routing or grinding bit for this type of work.
It is WAY too easy to damage the area around the flood hole.
Sand down the plastic from the inside of the “hull” until the hole
opens “by itself”. Power tools, unless mounted in a machine
risks unwanted movements of the machine.
Plastic needs to be worked at low rpm’s to avoid melting.
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The globe shaped steel sutter. I have used it for exactly this purpose. You have to go at slow RPM though. You want tiny chips of plastic. You don’t want to melt it. For really small holes, like on the back of the fairwater on a Gato, countersick from the backside with a hand twist bit about twice the diamater of the hole. You get a lot better control this way, and the hole will look like it’s in plate steel rather than tank armor if you’re careful. 
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I second @18bravo’s recommendation of the ball cutter. They’re available down to about 1/50 of a inch diameter and when mounted in a good rotary tool of the type @TopSmith recommends are very controllable. I have a Foredom model that turns happily as low as 10 rpm (or slower) with good torque. They can be pricey but a good one lasts - 20 odd years of not always gentle use for mine.
All that being said, the only solution I’ve been happy with was to cut out the holes as best I could and overlay the flood holes with photoetch parts slightly recessed to match the hull profile.
Cheers,
Colin
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Should have asked which sub you’re building. If it’s a IXc, Uncle-Heavy’s sand from the inside will work well as the moulded in holes are nice and deep.
My two cents.
Cheers’
Colin
It’s the Type VII but to your point I’m taking your advice and using sanding blocks from the inside. It will take more time but I think it’s safer and will look a lot better in the end. Thanks
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