I have a very rigid cnc router. It has a high speed spindle which isn't very good for cutting steel and aluminium. The router is also very open so cutting with coolant is out of the question.

I want a slower spindle, something like this...

BEST Spindle with synchronous belt for CNC milling BT30 ATC petal clamp+ disc spring+drawbar-in Machine Tool Spindle from Industry & Business on Aliexpress.com | Alibaba Group

The plan is to initially use it on my router, then in the future, build my own small desktop mill that can cut like a golmatic (1.1kW spindle ploughing through cast iron)...

GOLmatic MD23 & MD22 Demo - YouTube

I still need to select a motor/controller/gearing that will give my speeds (I'd be happy with a max of 5000rpm and min 50-100).

And pick a method to operate the draw bar (air/electric)

And work out how to get air flushing working.

And how to automatically change the tools.

(lots of fun projects)

Anyhow...

Is there anything I need to be aware of (wary of) with these spindles? I can't seem to find many example projects using these.