The Natural Philosopher wrote:

Dear tabby. PLEASE read what has been read. We are not talking about a
3mm dia cutter, but a 40mm or gretaer diameter cutter used on edge like
a precisioon saw with a 3mm kerf.

e.g. This axminster 47mm cutter, which with a 22mm bearing on the arbor
will cut a 12.7mm groove, unfortunately they don't seem to sell e.g. an
19mm bearing arbour which would give the 15mm groove required.

http://www.axminster.co.uk/axcaliber-2-wing-slotting-cutters-ax809783

Or they do a 4mm x 15mm intumescent slot cutter, if a 4mm groove would
do instead of 3mm?

http://www.axminster.co.uk/axcaliber-intumescent-strip-cutters-ax834745