Update: Adding ventilation aka the swiss cheese offensive.
To improve the air flow in this case not only do I plan on adding a 140mm fans to the top and front, but also adding some ventilation holes in the sides, behind the plastic side decals.
I wanted to cut some holes out from between the fins it the same way the front of the decal is cut.
Here's a pic to remind you what it looks like.
To start with I carefully marked out two holes, that cover about 60% of the length of the decal.
I didn't want to make them any larger or a single hole as I don't think the plastic is strong enough.
It is possible to see from the back side where the fins roughly are and I was hopeing to cut it out from this unpainted back side to help preserve the paint work as much as possible.
I started by drilling 4 holes in the corners of each section I planned to cut out, but on investigation of the back side it's just too indistinct to know where the fins are.
As the fins are not straight I didn't want to risk cutting it from the back.
So I just had to be careful and work from the painted outter side, out with the rotary tool and get cutting.
As you can see from the image this has not been a neat or easy job, which is why I gave myself lots of clearence and didn't want to risk cutting from the back side.
You may also tell from the image that I tried many different bits, with varying degrees of success.
Both the normal cutting disc and saw disc could cut down a couple of mm but then got to awkward to go much deeper. (this plastic is about 5mm thick)
The best bit I found for this was the larger of my two small milling bits (I think that's what they are called)
However it still took multiple passes and I could only work small sections at a time.
It was a slow process but I finally got the 1st section cut out
As you can see from the bit, the biggest issue I was haveing is that it was not so much cutting but more melting it's way through.
The molten plastic both wrapping around the bit and resolidifying in the cut behind the bit, meaning I had to constantly go back over it just to clear the cut.
After getting half way through the 3rd line I had to cut I was so fedup with it I decided on a new tactic.
The trusty spare hacksaw blade and elbow grease.
My reason were, that I'd had no hassle makeing the holes with my hand drill so I was unlikely to saw so fast that I'd melt it as I was cutting
And the ease at which this methord had worked on the aluminium which while soft is still harder than this plastic.
It worked a like a charm Once I'd drilled some extra holes to get the blade in to start the cut.
Cutting the rest of line for this first section this way took half the time it had taken me to get this far with the rotary tool.
With the first 4 sections removed and time getting short I decided to just clean up the holes.
I first tried my files, however they are too fine and designed for metal so gummed up fast with plastic dust.
I then tried whittleing the excess off with my stanley knife, this was better but was still going to take too long.
I had an idea and tried to use a drill bit as a cutting bit, it didn't work very well.
Thinking back to my work with the aluminium I thought I should give the rotaty tool sanding drum a try.
The sanding drum is too large to fit in the holes So I gave the grinding bits a try.
Success! after trying a couple to find the best one and best technique, I was soon rappidly carving away the excess.
I didn't take a pic of the bit, it's the largest one I have, that still has flat sides.
It looks like this, only a bit thicker
I worked along the length of each cut, slowly nibbling away the excess as I went.
I think the combination of the larger diameter and sanding rather than cutting action of this bit is what made it work.
I still did get some melting, but not as much and what there was didn't get in the way or wrap it's self around or coat the bit.
I then used my stanley knife to trim off any melted flashing, give it a quick shave to smooth it and square up the corners.
To shave plastic, use a decent knife (craft knives can work but the snap off blades are often too weak) hold it at 90 degrees to the surface, as if you're going to cut down into it.
Then draw the blade across the surface, you'll shave off thin layers and get a very smooth finish
You could hold the blade at an angle like the blade in a shaving razor, however I find this cuts down into the surface too much/often and 90 degrees works better.
Here's the final resault
ok this one is not quite the final resault, this is before I finished Stanley knife trimming
At this point I regret drilling the holes for the 2nd cut out section as I don't think it'll be needed.
I did manage to catch the silver paint a few times and the shaving removed a lot more from the sides of the fins.
I'll probably have to fill the holes and repaint these side decals when I'm done.