how to route a thin deep slot in end grain of 18mm wood

[John Rumm]

By "later", do you mean a hour and four minutes earlier by any chance?

[John Rumm]

I have never broken a 1/8" router cutter (or any other for that matter)...

(chipped a few though)

[RJH]

Actually yes - I didn't take into account the 3mm from edge part. But if it's a reasonably sympathetic blade, well worth a try. I clamped a piece of wood to the bench as a guide rail and I was very surprised how good it looked - and that was a 5mm strip at most.

[The Natural Philosopher]

Actually no. A good router tool will leasve a 10 thou wafer standing if you set it up right.