It depends on what you expect the machine to do. 200W is not much more powerful than a Dremel tool, which is 135W. You'll be able to mill out stuff with a 3mm or 1/8" end mills with a depth of cut (doc) of about 1-2mm depending how hard the wood is, at about 300mm/min and how sharp the end mills. I went with a 1.5kW spindle, it can easily plane a piece of fresh oak wood with a 16mm planing bit at 5mm depth of cut and a load of 40% (40% of the 16mm diameter of the end mill engages with the wood) at 1500mm/min. Being able to remove large amounts of wood is great when 3D carving. You can usually do a roughing pass to remove most of the material with a stock to leave of 1mm, with a large flat end mill, then use a small ball nose end mill for the detailed work.
500W spindles would be a better start. If you build your own frame make sure it can support heavier spindles if you wish to upgrade. You'll be able to mill small Aluminium projects too, depending on the rigidity of the build. I've build my corexy printer by milling out aluminium plates and using 20x0 extrusions (which my CNC is also build from, which is an openbuilds OX).
1.5kW spindles will get expensive quickly since you need a variable frequency drive (VFD) to run them (they convert AC mains to 3 phase AC for 3 phase spindles). The VFD does make the spindle very powerful, and can supply more power depending on load making the spindle rpm constant instead of dipping, which normal spindles tend to do. If the load gets too high, the VFD is smart enough to cut the power to prevent damage. Good spindles usually run quieter compared to router spindles.
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Kind regards
Imqqmi
NFAN CoreXY printer:
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reprap.org]