I have been cutting on an old oak. Its huge, maybe 3 to 4 feet in diameter. It blew over around 5 or so years ago and it seems the longer its down the harder it is to cut with my saw. The trunk that I have been cutting is up off the ground. It seems like I cant cut for 20 minutes without my saw getting dull. Is this a know things that people have had trouble with. I dont notice this type of problem with the red oaks. It s bad enough that Im considering not even messing with it from here on out, as I have plenty of other good wood, and I can be choosy. I can cut maybe 20 big rounds and my saw is dull. I have a Stihl 290 farm boss, 18 in bar. thanks,bd