Have big disc chipper, awesome machine to work with, Morbark 2100D 15" disc. MASSIVE machine to tow, but fills big truck very well, easy and inexpensive to maintain and it is very simple to sort out knives and work on despite its shear girth, chips big tops well and has 'crush/lift' feature meantioned above to help material through. Its very important to keep a close eye on anvil sharpness and adjustment, makes a big difference on a disc. Drum has its place but the bearings are very expensive to replace and if your unfortunate enough to own a bc1000 and try to chip wood with it you will find your drum is also very expensive to replace. I have heard very good things about the 990 however and the Morbark 15 and even 13 were good drums for sure.