I have an approximately 20 year old TroyBilt Super tomahawk
chipper/shredder that has just had its first full replacement of all 16 hammers.
Most of the
chipper/shredders that are built for PTO use are built similarly, from what I have seen. The
Chipper feeds into a blade. The shredder feeds into the hammers. The chips from the blade pass through into the shredding chamber as well Most larger
chipper/shredders have two blades, my 8hp unit has one. The hammers are much, much faster than the blade. They handle material (in my machine) up to 1/2 inch, and they suck it in very quickly and shred it with tremendous force. Surprisingly, (not really when you think about it, though) brush, particularly dry brush shreds much faster than leaves, which are more strain on the machine and take longer to process.
The blade part (
chipper) works fine on bigger material, but much slower, and the blade wears much faster than the hammers. If you burn wood for heat, I think you will find, as I do, that the shredder gets 90%+ of the work. A a lot of the stuff that goes into the
chipper part is already rotten or otherwise unsuitable for firewood.
There are certain types of wood that give the machine particular fits, and by far the worst that I have ever run across is hawthorn. This wood is tough and fibrous and raises **** with both the blade and the hammers. In addition, the thorns are more than capable of penetrating the tires of outdoor power equipment, which I learned to my chagrin with my DR Powerwagon this spring.
Sharpening the blades takes equipment that can precision grind a bevel, so you either have to get that kind of equipment (the only one I know of made for home use is made by Mikita and sells for about $250.) or find a sharpening service that has the equipment to do it. I have accumulated a set of 5 blades for the Troybilt, and when they are all sharpened I can usually get a couple years out of the set before going back. Keep in mind that I chip/shred maybe 3 full days a year, spring and fall, and you might do a lot more or less of it.
Dry wood and brush feed much more efficienty than green, especially in the
chipper side because the bark can get twisted into the machine and cause real problems when green. It's best to turn the wood as you feed it, and occasionally pull it back to be sure it isn't being twisted into the machine.
Since I bought a tractor this summer (New Holland 26 DA), I will eventually be looking to replace the old troy-bilt with a bigger machine that runs off the PTO. I would never consider one that didn't have the shredder capability, because from experience, the greatest amount of stuff will go in there, and of course, the bigger machines have larger than 1/2 inch capacity in the shredders. The larger capacity on the
chipper (4 or 4.5 inches instead of 3) will be much more welcome for its ability to better handle branches that aren't straight rather than larger ones, again, because branches or limbs this large are suitable for firewood. While units that have only the
chipper part might have some uses somewhere, I have about 30 acres of wooded property, burn wood for fuel, and have found the
chipper/shredder type to be the most useful machine on the place. I would recommend to anyone, unless they are going to get a really large
chipper like the ones the tree surgeons use, to get one with the shredder hopper, because that's the most useful part of the machine. Most of the hammers have four "corners" that can be rotated, and they last a long time, as I mentioned, my original set lasted about 20 years.
Oh, and here is one very small piece of advice that I learned the very hard way.. Nobody in their right mind would ever use one of these machines without good eye and ear protection. Gloves that have some padding to them help with the chipping part. Always wear protective equipment, but NEVER, repeat, NEVER use the kind of hearing protectors that go inside the ear. Use the earmuff style ones, because I can tell you that until you have had an ear hit by a flying wood chip, you have no idea the kind of exquisite pain an ear is capable of rendering. It's kind of comical to think about it in hindsight but I think I actually cried from the pain from that sucker, and was wanting to laugh at my own stupidity at the same time. Lastly, because goggles fog up easily, (and I don't trust any other kind of eye protection), it's best to reserve chipping for the cool or even cold weather. Since most four cycle engines run at peak hp at 32 degrees, you'll get the most power out of your machine that way, though of course, a 1% dropoff for each 10 degrees isn't a big deal.
From what I've seen, the newer
chipper shredders carrying the troybilt name are nowhere near as heavily built or as heavy duty as the ones they had in the era when mine was made.