I am trying to cut perfect circles about 100mm in diameter. The file gets about half way complete and decides to plunge straight into the acrylic. I believe it is a tool heating/ wrong tool type issue but wasnt sure since I am new to this. I am using a sold carbide 1/4 in fish tail double flute. Each pass only takes off about 1mm of acrylic. After 3 or 4 passes i can hear the router struggle and it plunges into the acrylic. I am using PORTER-CABLE 690LR router. Any suggestions?