Nick,
The issue with steel on aluminum is that aluminum ends up with an oxide coating -- the same stuff normally associated with "sandpaper." It is counter-intuitive, but aluminum will wear most steels long before the steel wears the aluminum. In normal usage, this should not be an issue so long as you lubricate surfaces each time you use it. A thin UHMW PE (Ultra-High Molecular Weight Polyethylene) washer is another cheap and easy solution.
To those who will say that I am being too conservative on this, I had a customer back in the 1970's who made parts that had to be cut and routed using long aluminum skate tracks. The skate carriages were made out of medium carbon steel with a heat treated glide plate. The carriages would be worn to non-compliance (tolerance) within 100 parts. A simple UHMW PE insert solved the problem. I have run into this exact situation with fair regularity, so I am sensitized to the more than most.
Good luck with your radius cutting attachment.
