Forget alu.
99.9% of all tools in the world able to cut steel, are cast iron or steel.

If You wanna make watch parts, it´s not hard but a bit expensive.
Everything needs to be upsized 3x vs a wood router, and preferably 10x the mass.

Expect about 5-10k in costs for a medium diy setup.
No ??
The worlds best guys regularly spend 20k for similar.

I sold a similar industrial setup, 5 axis, for 100k€.
To one of the worlds best watchmakers, Pita, in Barcelona.
Pita is the Only Spanish member of the Swiss watchmakers horological society, about 40 members.

You *can* cut brass and alu parts with anything light, like a chinese barebones router.
But they wont be round or cylindrical or repeatable to watchmaking standards or metrological standards.
You will need to mount adjust and finish every part individually, to size, flatness, square, cylindricity, etc.
Pita used to do that.

Until I sold them the Haas OM-5 axis office mill.

And it was a knife-edge decision by Haas to approve the specs that premium watchmaking needed.
Because Haas will never ever fail, (at least Hitec Mexico and Spain) and will fix anything at any cost, they ever sold.
I know, I was part of the executive.

I personally sent the case to Oxnard, cali, and they guaranteed that the Haas OM would deliver.
They were happy with the product in Pita Barceloa.

I´m NOT saying You need to buy a HAAS mill, to do Your work.
I´m pointing out that repeatable work, watchmaking, comes out from good machinery.
Reducing manual rework.

Potentially, changing the screws (ground c0), mounts (ac bearings abec5+), linear guides (heavy preload precision class), and using industrial epoxy to fix a granite base under the bed You would get a good tool out of a basic router.
Then change the router to
1. high-speed spindle, water cooled, == 800w (you don´t need power),
2. Nakanishi NSK.