One thing to check in the actual cnc program, would be to make sure that there is an \"M31\" within a few lines of code after any tool changes. This ensures router is up to full speed before continuing cut. If this line of code is not after each tool change, it is possibly that the spindle could stop and the machine axises could continue exicuting program.
Hey guys, It still sounds like you may have an loose armature wire or a neutral wire in the control losing connection somewhere. It may have ran for a while after you replaced the frequency converter because the wiring was moved around. Now, the same problem has come back. A technician is coming there on monday to check it out.