I have a 20 tooth Ø3.00 x .375 wide side mill cutter with a custom form grind for my product. I ran over 500 parts then I sent it to my tool grinder for sharpening and only got half the tool life as when new. It is made out of M42 what would be the best coating to apply to it? I am cutting 6061 T651 aluminum. Also where can I get the coating applied?