In article . com,
mark wrote:

Could you use a router at slow speed with a small 1/4" endmill on
steel or aluminum taking very light cuts with coolant? How about a
1/4" spiral up carbide woodworking bit?

You can route aluminum, but steel is hopeless.

Woodworking bits may be too light, unless we are talking about trimming
the edge of a piece of thin sheetmetal.

Coolant recommended for thicker stock, but what a mess it will make.
Bit spins at 10,000 rpm min, and will throw the coolant everywhere.

Coolant must not be flammable. Water-based coolant recommended. But
keep it out of the router motor and bearings.

This isn't sounding like a very good idea, even if you can make it kinda
work. What are you trying to make?

Joe Gwinn