Cutting Vents

The object of this article isn't just to cut vents - in this case the kind with parallel sides and rounded ends - but to do so in a way that is as hard to screw up as possible. It's still fundamentally a tricky thing to do, so practice first anyway, but this is the careful approach.

Mark out the area you want to cut (if you're cutting out an existing recess this is obviously done for you already, and makes the whole thing easier.

Drill series of holes to take out most of the 'bulk' of the area you want to remove. (This is a common trick to remove sections of existing pieces.)

Use a small pair of clippers between the drilled holes (CAREFULLY!) to clip out the centre section that's waste.

Use a sharp knife to shave off most of the plastic up to, but not quite meeting, the edge.

You can use the side of a drill bit (so long as the bit is wider than ~1mm, otherwise you risk snapping it accidentally) a bit like a circular file to cut a round corner at the end. You may have to 'drill' it a little in the first place to get it in, be careful not to go off-centre if you do.

If you want square corners then you'll have to find something square, like a neatly-cut bit of thick styrene, and glue a bit of sandpaper to it to do this stage. I've ended up using a sharp blade to carefully slice the deepest section of the corner to actually be square in those cases 'cause sandpaper typically doesn't give a sharp enough inner corner when it's folded over something.

Glue a bit of high-grade sandpaper to a thin strip of plastic. I'm using 600-grit and ~.66mm styrene here - it just needs to fit inside the vent, basically.

Very Gently sand down the inside edge - it'll take time, longer if you didn't cut very close to the edge with the knife earlier, but you get a lot of control when you're sanding lightly and it's important to not sand too much off. Finer-grit sandpaper sands slower, don't go too low. As always, wet the paper first to carry the plastic dust away.

After this stage you may find you need to go back and file away with the drill bit again if you sanded too far into the corner.

Polish off the front lightly with another bit of high-grit paper, to make sure the front corners of the edges are nice and square.

There you go - neat vent with rounded edges.

You'll also probably find the whole thing easier (or at least, quicker) if you sand the width down a bit from the back so you're not cutting through so much plastic...

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