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?

Forget steel. Even if you can get the speed down the chatter is going to
wipe out your carbide em.

The spiral up carbide sounds like it might work in aluminum but be prepared
to ruin it. If you are trying to get any sort of depth in aluminum, I
wouldn't try for an end mill diameter slot. Better to go with reduced
diameter so you won't be bouncing against both sides of slot.

This opinion is worth what you paid for it Report back results.

Wes