What Did I Do Wrong?

[Bill C.]

Fly cutters are used to cut large areas like a face end mill. If the chips are dark blue then the speed is to fast. I have used HRS and I know its used for weldments all the time. I've used angle iron to make small angle plates after cleaning the outer surfaces of scale.

I never used a coated end mill that I can recall. Not sure why they are coated. I would ask HF to replace the end mills, can't hurt to ask.

 

[gaston]

looks like you took too light of a cut and didn't get thru the plasma affected zone. I have done the same thinking I was being easy on the tool.
you need to cut deeper and slower till you see how it reacts. As for not useing carbide in a hobby machine, I think thats BS. I have used carbide end mills in a drill press many times to "fix a screw up"to cut hard material that ate a drill or tap and never hurt one.(be careful as they are easy to chip). Can't beat carbide tooling for dealing with hard stuff.