[Jim27]

Looking at milling with some 3/16 to 1/2" end mills and some profiling with ball end mills. Looks like AlTiN coating is not a lot more. About $11 for carbide 3/16 ball end mill and less than $2 more for coating. Is there any down side to the coating? I am guessing it would not be good for Aluminum and some other materials. Just a hobby shop so would be good to be able to use them on different materials but the 4140 project is significant so other use is not a big factor.

[joeavaerage]

Hi,
I personally buy coated tools especially for steel and stainless. They also work in just about all materials including aluminum, so I don't see any downside aside from cost.

AlTiN is a trivalent coating and has affinity with aluminum which is also trivalent and is not therefore recommended despite that it works. The best coating I've ever tried
for aluminum is either no coating at all OR Titanium-di-Boride. It's a 'greasy as a butchers prick' in aluminum, just the ticket for sticky 3000 series and some of the stickier 5000 series alloys.

Ferrous metals are tetravalent and AlTiN shows good lubricity in steels.

I don't know about you but I need all the help I can get to get good tool life and coatings are a part of that.

Craig