What bits are you using to cut 4" thick hardwood?
You might try blowing a stream of compressed air right on the bit. ENCO sells a unit with a magnetic base, a valve, and two flexible loc-line nozzles for about $25. The plate on our model 40 that holds the spindle motor is steel, so the magnet works there. you can cut a hole in the yellow dust shroud to pass the nozzles thru, and aim one on either side of the bit.
Not only helps clear the kerf, but cools the bit, too. You might even be able to tap into the compressed air supply at the top of the z axis. Ask Thermwood first.
Docket Legal pad; Eagle USA, HB, #2 pencil; Radio Shack C100 solar powered calculator.