Front vents - Part Three

After I was done with the hole saw I used a sanding drum, that I made to go in my drill press, to finish the inside of the vent surrounds. The outside diameter is the right size for the curves on the inside of the vent surround.

 I then marked out the four corners that needed to be removed. The width from the inside to outside is 5mm and so I used a washer with this thickness running up against a cylinder that I clamped on the inside of the vent.

I then trimmed off the excess with a saw before sanding the outside to the correct shape.