Having trouble with stainless warping when I'm cutting it and wondered if someone could help. I have a piece of 3x50x500mm flat stainless 304 and cutting into 15mm widths. I clamped it down to a piece of ply with another piece of flat steel as a straight edge then ran the angle grinder back and forth till it was about half way through then took off the straight edge and finished the cut. Used a1mm slitting disc and kept it moving as I cut through. It's now bent as per the picture. What am I doing wrong?