The Cowells ME90 should deal easily with 18mm silver steel.
If you are getting belt slip I suggest you should use the backgear. In any case I would start with 240rpm.
I use HSS tools and in this case would want around 10 degrees top rake (opinions vary). Make sure the cutting edge is really sharp.
If the cut is any length I would use the auto-traverse and probably a touch of neat cutting oil.
I have not tried this out but I would expect a 0.5mm cut to be reasonable. Perhaps less to finish.