the spindle i choose is a normal router, it can take quite a lot of momentum, since the tools for machining wood ( its normal purpose) are quite long, thus generating a lot of momentum.. if it can withstand that kind of force, i think it will even do hardened steel.( not that i intend to, but just in case...)
i did a "test cut" with a standard HSS end mill, 3 mm @ 32000rpm ( cuttingspeed 300m/min) it will "eat" thermoplastics with hardly any burrs..
this is very nice, because this will enable me to make Sheet Styrene model kits.
To do this, i will glue a sheet of styrene ( evergreen ) onto a Nylon plate, with a waterbased glue, bolt the lot on my machine, mill out the contours and Hey presto!!,, parts like brakediscs, wheel spacers, or small parts to create assemblies, like why not even ship models?... mill out the bulkheads, and cover the lot with styrene sheet..