Poor Surface at LOW Chipload as well as Perhaps Deflection?

[coryatjohn]

By 1.4" I'm guessing you mean 1/4".

You are going to break end mills. That is a given. When you get to the point where you don't is a matter of experience. I suggest not using Onsrud bits for your testing. They are way expensive and give no meaningful advantage at the stage you are in with your experimenting. Buy some cheap end mills from Amazon or Ebay with no brand. You can pick them up for $10 or less each.

[EricSchimel]

If you're running the right feeds and speeds unless you run over a clamp it something you shouldn't be breaking bits.

If you're in the ballpark for the right feed and speed you won't break anything. Right now you're not even close to being in the ballpark

I'd follow some suggestions here on what people are running and start with those settings. Onsrud had decent phone support too. You can always call them and ask them about feeds and speeds.

To echo what Bill said... Spinning faster and moving slower is not the way to get better cuts and more life out of you're bits... Somewhat counterintuitively it's the opposite. Crank up that freed rate and drop your spindle speed!