Thanks Irving - a great reply.

Fortunately, my router (a Proxxon BFW 40e), has a range 900rpm-6000rpm, so dropping the RPMs is not an issue.

That said, it's only 250W...which I guess isn't great wrt cutting steel - I guess it'll be a suck & see job ....need to order up a 2 flute cutter & give it a go.

Would it be better to go with an even thinner sized endmill? (say 2mm diameter )....my thinking here is the less steel it has to channel out around the part, the less stress there'll be on everything? But then again, I guess you've then got to start wondering about the physical strength of the endmill at such smaller diameters (ie snapsville)?