Quit buying cheap router bits. Just joking, but seriouly don't by the bargin bin bits. Your probably getting the heat build up because the bits are dull. Oak will eat up the blades in no time, so you need a good bit. When the edges of the bit are dull, you are causing your Hitachi to do more work, hence more heat build up. Also blow out the motor vents, so you can get some nice cool air to enter the motor housing and cool things down. It is natural to get some heat, but not excess heat.