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  1. #1
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    JD2305, 1948 B.F. Avery Model V

    Default Chipper Designs - Hammers vs knives?

    Is there an opionion here as to whether chippers designed using knives for the chipping function operate better, worse, or basically equal to designs using swinging hammers (all other things being equal). There seems to be many here advocating machines incorporating one or the other although I haven't yet seen this aspect of the design come up as a criteria for selection.
    JD2305 w/ 62MM, 200CX, Markham toothbar, RB1060, sprayer, Ballast,
    1948 B.F Avery (Model V)

  2. #2
    Elite Member RalphVa's Avatar
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    Default Re: Chipper Designs - Hammers vs knives?

    I think all chippers, at least on smaller hp rigs, have knives. Shredders use hammers. Some chippers have both: MacKissic, TroyBilt, DR maybe offers both.

    The knives cut chips from the ends of wood inserted and throw it out a discharge. Some have fans to assist the throw.

    Hammers just smash wood into pieces, generally only for smaller stuff with size depending on hp: hp goes up by square root of diameter ratio. Smallness of pieces is determined by the outlet screen. With a finer screen, the hammers smash it more and more times until small enough to go through the screen.

    Ralph
    The natural gardener
    God's original intent

  3. #3
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    Default Re: Chipper Designs - Hammers vs knives?

    RalphVA,

    This is what I would have thought also except that I currently have an old (circa 1975) chipper shredder which has the small chipper chute feeding the hammers and the large shredder hopper feeding a single small blade, mounted on the motor shaft like lawn mower blade within the radius of the hammers, and then material is thrown through the impellers/hammers and out. The small stand alone chipper/shredders like the Mackissic (http://www.mackissic.com/consumer/le...sumershred.htm) look similar to mine except that the chipper chute is on the chute side, not the motor side.

    Looking at the mackissic photo, if the knife is on the chipper/motor side, then is there also another blade (perhaps called something other than a knife) on the shredder side? Otherwise it's not clear how the shedder material is passed solely into the hammers without being feed into the impeller area within the rotating disk of the hammers due to size of typical shredder openings. Also doesn't seem like feeding even small sticks directly into the impeller area would be good on the machine.

    Also confusing is that mine also has an additional panel behind the shredder hopper who's purpose I've never quite figured out except that it also a second path for material to enter the shredder (if I have my terminology correct). Perhaps I've somehow gotten terminology mixed up somewhere or I've got a real oldball unit coloring my understanding of how these things work. I'm wondering if what I originally thought was a knife on the shedder part (single spinning blade which cuts twice per revolution is really just a blade - definitely doesn't mount/look like planer type blade). Thoughts? I'll try and get a photo or two to post.

    Any case, are you saying all "chippers" today are knife based?
    JD2305 w/ 62MM, 200CX, Markham toothbar, RB1060, sprayer, Ballast,
    1948 B.F Avery (Model V)

  4. #4
    Gold Member MiserableOldFart's Avatar
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    Default Re: Chipper Designs - Hammers vs knives?

    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.

  5. #5
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    Default Re: Chipper Designs - Hammers vs knives?

    So naturally my first usage of the chipper/shredder is for clearing out hawthornes...

    Attached (hopefully) are two photos of the chipper/shredder. Note no knife on chipper and shredder with blade/hammer combo. Inherent design, coupled with limited throat capacity, coupled with challenging material (Hawthornes) probably explains it less than stellar impression so far.

    I realize the thread has morphed from my original intent, but the information has been useful trying to figure out where to go next with this.
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    JD2305 w/ 62MM, 200CX, Markham toothbar, RB1060, sprayer, Ballast,
    1948 B.F Avery (Model V)

  6. #6
    Elite Member RalphVa's Avatar
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    Default Re: Chipper Designs - Hammers vs knives?

    ADin,

    That's a really odd machine. My experience runs along the lines of OldFarts.

    I also had a 20 year old Tomahawk that I'd sharpened the chipper blades on a number of times and replaced or turned the hammers about 3 or 4 times. Did it one more time before selling it. I always just sharpened my chipper blades on my monster grinder by placing the blades along the side of the grinder wheel. With my big grinder, this is easily done. Just have to slowly do it to keep from overheating the tempered blade.

    My Mac is like the Tomahawk, almost identical, except the Mac doesn't have through-bolted blades and has A BUNCH more (and maybe harder? No wear shown yet) hammers.

    Yes, about 90% of the stuff you'll do wants to go into a big chute and to the hammers. That Unico seems to be designed all wrong.

    For leaves, the Mac is MUCH superior to the old Tomahawk. There's a section of the chute that can be lifted up out of the way to allow a bigger hopper for putting leaves into. Still, you have to kind of dribble them in. Can't just dump them. Do this, and you'll need a stick to make the leaves drop. The Tomahawk was really tough to do leaves with.

    I had a Mac that went onto my Gravely that was a shredder only machine. I used it to do the leaves before I got the JD and the Mac for it. Missed the chipper on that made-for-Gravely Mac.
    The natural gardener
    God's original intent

  7. #7
    Super Member Highbeam's Avatar
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    Default Re: Chipper Designs - Hammers vs knives?

    "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."

    That's freaking hilarious. You have a way with words.
    Kioti CK30HST, FEL w/toothbar, 60" RC, 60" BB, PJ 10k trailer. Weekend warrior hauling 50 miles each way.

  8. #8
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    Default Re: Chipper Designs - Hammers vs knives?

    I can definitely relate to the ear pain and will paint you another picture for you to have a good chuckle over...the memory was so bad I had mostly blocked it out but maybe sharing it here will allow the mental healing process to begin.

    My hatred of the hawthorns that I am now in the process of clearing came about as a result hooking my ear on one of those wicked 2" thorns when trying to cut close and under one on my JD335 (ducking + lifting limb with left arm -- whoops, hand slips). Between the initial piercing pain causing temporary loss of motor skills, I traveled another 1' or so before I came to my senses and got my foot on the brake. At that point I'm stretched out and nearly pulled off the rear of the tractor as the limb is now under tension and I'm caught like a bass on the hook. Everytime I move at all I am jolted with excruciating pain. As I try to reach up to unhook myself I realize this crooked thorny limb has side limbs wrapped across my forehead and top/back of my head. Everytime I move any part of the tree limb (which I can't actually see) I either grab a thorn with my hand or some part of my head is pricked by a thorn. After what seem like an eternity, I finally manage to extricate myself from my crown of thorns. I sneak inside to clean up as I now realize I look like I've been in a horrible chain saw accident and will freak my wife out if she sees me first. The hawthorns may have won the battle, but I vowed to myself that day that I would win the war. It's been tit for tat between me and the hawthorns for the past 3 years, but D-day for the hawthorns is coming this weekend. Fortunately for me, no permanent damage (hole in ear closed up quickly) except for the longterm mental scarring that I'm sure I suffered. Come to think of it, I think I'll go out and some pour salt on the spot where that hawthorne once was...

    Oh, and later that day I realized my 335's front left tire had also fell victim to the hawthorn's wrath. I've patched thorn punctures multiple times since and to this day I still have a very, very slow leak in a rear tire which I can't find but know is related to the hawthorns. It's became a "thorn in my side" so to speak that I live with to this day...
    JD2305 w/ 62MM, 200CX, Markham toothbar, RB1060, sprayer, Ballast,
    1948 B.F Avery (Model V)

  9. #9
    Elite Member Cliff_Johns's Avatar
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    Default Re: Chipper Designs - Hammers vs knives?

    So ADin,
    I think the piece of information you may be missing is that there is a slot behind the blade on the chipper input of the MacKissic so when the chip is chopped, it passes through the flywheel and gets pushed into the hammers which hack it up until it falls through the screen.

    I don't know of any manufacturers that use hammers for chipping except where the material is less that 3/4" or so. You can drop larger sticks into the shreadder hopper on the Mac, but it makes one heck of a racket, and I try to avoid it.

    If you search on MacKissic, you will find a few reviews of the chipper/shreadder have been posted on TBN including one by me.

    Cliff

  10. #10
    Bronze Member
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    Default Re: Chipper Designs - Hammers vs knives?

    That's exactly how I figured it should work, but this goof ball chipper/shredder I've got through me off, especially since I never really used it more than a one time experiment. It behaved poor enough that I wanted to a) ensure anything I else I was considering was of a different design, and b) ensure that other units actually work better. Perhaps what I have is not technically a chipper/shredder per se, but just a shredder if such an animal existed. Any case, all is clear now - thanks all.
    JD2305 w/ 62MM, 200CX, Markham toothbar, RB1060, sprayer, Ballast,
    1948 B.F Avery (Model V)

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