I'm having an issue with snapping bits on my cnc router. Working with 3/4" boards, typically MDF, melamine or plywood, 1/4" solid carbide bits, 1/4" depth per pass. I believe it's an issue with the speed and feed rates. Currently set at 20,000 rpm. I'm finding conflicting info on recommended feed rates and as the problem is still occurring I am obviously doing something wrong. Any input would be appreciated. Thanks.