HarleyBob: hayden mentioned knife condition and this is something to consider. One of the reasons I purchased the smallest Valby is because the knives (2) were relatively large--about 4 x 8 inches. When you look at the specs for the smaller PTO-driven chippers, you'll see that the knives on some of them are quite small--2 x 4 inches or such. Knives need to be sharpened so ease of removal and replacement is another criterion. The dealer I worked with indicated that I would probably have to sharpen the knives each day and I had resigned myself to this but have found that I rarely have to do this. So far, I have removed the knives a couple of times and touched up the edges lightly and that's been enough. Although I sharpen lawn mower blades regularly and have no trouble doing so, I don't have the equipment to do a good job of sharpening
chipper knives. Fortunately, there is a local person who does custom sharpening. By the way, I purchased two extra sets of knives so that I can change around and keep working if necessary and also to have sets on reserve in case I can't purchase any in the future (in case we declare war on Finland and stop importing stuff from them). Bearings are another consideration hayden brought up. The ball bearings on some chippers appear to be rather small. My Valby has massive roller bearings which probably never will have to be replaced. However, when it is time to clean them and apply new grease (every 200 hours), it's going to be a pain. You actually have to unbolt the top half of a cast iron bearing housing and remove it to get at the bearing. No zerks here! Another thing comes to mind--belts. Some belts look pretty flimsy. It would be nice to have standard V belts which could be acquired locally instead of having to special order unique and expensive ones. Before I purchased my
chipper, I wondered if a direct-drive
chipper would create greater stress on the tractor than a belt-driven one and I talked to the dealer about this. He pointed out that a shredder (Bush Hog) is direct driven, so there shouldn't be a problem. I have found that the momentum of a heavy
chipper disk absorbs shock nicely. When my 220 pound disk is revolving at 540 rpm, it takes alot to slow it down; you can imagine what the same disk would do when belt drive and revolving at about 1,500 rpm (more or less; I don't remember the exact speed). One last item; some of the belt driven chippers have heavy, cast-iron pulleys that contribute to the momentum of the disk. When considering the weight of the
chipper disk, you also need to add in the weight of the pulley.