I like the stamp!
Looks like you’re using one of the cutters meant for drilling PCB vias. Just thought I’d let you know, we also do a lot of milling here with very small endmills. McMaster sells a series of solid carbide endmills in very small diameters; they’re pricey but also they last forever with soft materials (we mostly cut polycarbonate and ABS with them).
Since they’re meant to mill from the side, the aspect ratio (length to diameter) is much lower, so they’re much more rigid than a via drill. You might be able to run at much higher feeds that way, without breaking the cutter?
The image I’ll paste in below shows an 0.7mm endmill; they get much smaller than that though.
Just a thought!
Nice work anyway!