I'm working on a personal project and am cutting some 3D characters from 20lb HDU. For the roughing pass (1/2" end mill) I was running it at 6 IPS and am doing the same for the two finish passes (1/4" and 1/8" bullnose bits). All bits (other than the 1/2" end mill which came with the shopbot starter kit) are Amana brand. I had already run this project but neglected to allow anything under my 3D model and so it broke free and the job got ruined. My own fault I know. Was I just lucky with running at that speed that nothing broke? The bullnose bits are nearly brand new, this being just the 3rd or 4th thing I've cut with them, all being cut in 20lb HDU, 1.5" thick if that matters. Could I run it even faster for the finishing passes or am I already pushing the envelope?