What's this Carbide coating.

[Boyan Silyavski]

I remember somebody using plan drill bits for the purpose. A good bit like Dormer is quite balanced. Leave, flatten or ball nose the face. But a proper reamer I belive is what will do the job.
As you can see bellow more or less the special foam cutters look similar.
http://www.3dcutting.com/solutions/frogtools.html

so why not just buy proper foam cutter or try some of what I suggest for a diy solution

Look at this baby
http://www.ballewsawandtool.com/inde...hk=1&Itemid=31