I am currently doing microfluidics research and kind of stuck on this situation.

I am using a 0.79mm or 1/32 inch tool to mill a "bean" shape that is 1.2mm wide on a Polystyrene sheet.
However, my tool keeps breaking after milling one "bean" shape on a polystyrene sheet.

I used 7000rpm and 250 mm per min.

Can anyone of you give me a tip or method that I should take to successfully mill without breaking the tool?