Bits keep breaking

[graysenKobi]

I’m trying to rotary a car model again using poplar and being mindful of the pass depth recommendations of my bit. However, my robust hogging 1/4" bit keeps breaking during the first roughing pass! Do I need bigger bits like 1/2" for roughing? I’m reluctant to reduce the pass depth as it’s already 5+ hrs of roughing for initial pass.