So this is my first post so please bear with me. I just setup a new Kreg router table with a Jessem Mast-R-Lift II and Dewalt 618 2 1/4 HP router. The initial project I wanted to get done learning to use this new table was to simply make some speaker adapters for my car using some 3/8" King Starboard. I have a 1/4" spiral flush trim bit that I am using in the table and I am making sure to feed the material from right to left into the table rotating counter clockwise, the problem im getting is the bit will grab the material and leave a ton of chatter marks when doing this, I have the speed set at 20k rpm, im not sure if its a problem of not maintaining proper pressure into the material or the fact of trying to cut 3/8" with a 1/4" bit or if the material im trying to use just isnt router friendly. I am looking to make these out of plastic because water in doors will destroy MDF over time. Any pointers or help would be GREATLY appreciated.