Application: General-purpose Aluminum and Brass machining, both roughing and finishing. Recommended Surface Speed: Up to 1200 SFM in Aluminum Alloy. We've recently started offering a line of 3-flute CrN coated end mills that our machinists really enjoy. These tools have 3-flutes with a cutting geometry optimized for aluminum machining, but what really sets them apart is the performance CrN coating. There are four main considerations when evaluating a cutting tool coating: