On Sep 1, 4:31 pm, 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?

Mark,
This is definitely an interesting concept!
I feel that what you are trying to achieve is to make an impression
onto an aluminium flat sheet?
Would it be a better idea to get the top (Thinner) sheet cut by laser,
and then layer this on top of a solid sheet of aluminium, thereby,
giving the effect of indenting the top sheet with the pattern you
require?
Just a thought.
Best regards,
Anthony.