Chipper Chipper Designs - Hammers vs knives?

[ADin]

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.

 

[RalphVa]

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

 

[ADin]

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/leafshredderandchipper/consumershred.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?

 

[MiserableOldFart]

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.

 

[ADin]

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.

 

[RalphVa]

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.

 

[Highbeam]

"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.

 

[ADin]

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...

 

[Cliff_Johns]

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

 

[ADin]

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.

 

[jeffinsgf]

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.

Why would you want to chip hawthorn, anyway? What are you going to do with the chips? I would advise against using them as mulch. You'll find those thorns every time you work in your beds. My bane is honey locust. I use my chipper shredder a lot, but mostly on cedar. The honey locust slash goes straight to the burn pile.

 

[ADin]

I won't use the chips for mulch but will pile them up out of the way to decompose and occasionally add some to the compose pile when I need more carbon. Surprisingly, I looked for thorns in the chips and couldn't find any although I know there has to be plenty of them in there.

My main reason, however, for not burning is because the act of getting the downed hawthorns to remaining burn pile is still worst than chipping (need to cut everything down and load one wagon at a time). It's also much slower do to distances involved. I had many strategically place burn piles when I did the first pass of thinning about 5 years ago, but most of them were only borderline safe for burning and I since have relatively nice grass growing where I would need the piles to be. The only place for burning now is at the far back of my property. I also remember burning all weekend for weekends on end (I think 14 in total) in 90+ degree weather. The piles were so hot I could only get just close enough to throw the wood on (very miserable) and then I would wonder all night if I really got everything put out good enough since I didn't want to burn down mine or my neighbor's woods.

 

[veefre]

I'm out here on "only" 1/3 acre in California. However the property has tall chain link fences covered with English ivy, one is 12 feet tall, and I had to get a chipper/shredder to process all the trimmings.

So about 13 years ago I got a Patriot 6 hp CSV at HD. The price was good, under $400. I notice that a similar machine these days runs over $1000.

Anyway, the machine has two blades for the chipper chute (3" max) and about six hammers (I think) for the shredder rotor. It does a pretty good job reducing the ivy to compostible mulch - generally I can fill a couple of cubic yards of compost bin each year with just the ivy. The ivy nearly all goes through the shredder hammers - there aren't many straight stems that would need the chipper. However I do use the chipper knives to process branches from various trees I've planted that I've decided to stump (avocado, lime, lemon) or remove completely due to poor placement (too close to buildings or blocking sunlight for veggie garden.

The Patriot is a good enough machine. I can't compare its operation to others because it's the only one I've had. In the past 13 years I had to rotate the hammers once, and sharpen the chipper blades twice. I just use a 6" shop grinder to sharpen the blades - and finish off with a whetstone to remove the burrs. Have had no problems using this method. It's not like it's a precision chef's knife. I do like to do a staged sharpening, with a slightly blunter leading edge for more strength. But I doubt that it makes much difference. The last time I sharpened them (yesterday) they were still pretty sharp so I just touched them up.

The 6 HP Techumseh engine used to give me a lot of grief. That's until I figured out it has a pilot jet adjustment screw on the bottom of the carb bowl. Now I just enrich it maybe 1/4 to 1/2 turn for starting, and then adjust to where the motor runs fastest and smoothest at full idle. It burns some oil, always has, but I just top it off before each day's use and that seems to work out ok.

I also had to replace the outboard bearing about six years ago. Most likely because I used to hose the thing down to clean it inside and out while running, and some of the water must have gotten into the bearing. I don't do that any more, no need. I keep a spare bearing around just in case, though.

I'm a bit shocked by the price of replacement hammers, though. The current set will need replacing soon (already turned once), and the list price from Patriot is $75. Ten years ago I think the price was $40. Still seems to be a lot for just some cut, twisted, and hardened alloy steel bits (I'm a machinist). I've looked around but haven't been able to find any alternate sources, so I'm guessing these are unique to the Patriot line. I've thought of fabricating a replacement set, maybe out of 4130, but would have to find someone with a heat treatment oven to harden them.

Of course I've also learned not to put dry wood down the chipper or dry branches into the shredder. Dry sticks are abrasive and wear out the knives and hammers quicker than wet stuff. Make sure the big branches are straight so they'll feed themselves through the chipper chute. Dribble the ivy clippings in gradually, so they don't ball up and clog the shredder chute. Keep the collection bag flowing - a clog there will back up to the rotor and can cause the shredder to stall out. And then freeing the rotor can be a real chore.

I also find I have to wear a full face (beard) respirator when I trim the ivy - I'm a little allergic to the fuzz/dust the ivy produces and would rather not wake up the next morning with red eyes and a hacking cough. No hawthorne here, but I generally don't try to chip or shred roses or blackberry canes. Those go in the green waste for the county to worry about.

Most recently I had to service the rotor because the bolts holding the rotor housing to the motor loosened up and started making a squealing noise. Turns out three of the bolts had rubbed enough to wear off their grade markings. So I got new bolts, touched up the blades, and all is well now.

As far as ear protection and gloves... I will wear gloves when chipping straight stuff and easily managed leaves. However I'm a bit leery of a gloved hand getting snagged by an ivy vine and having my arm dragged into the shredder hammers. So I don't always wear the gloves. As for ear protection, the machine is not so loud that I feel I need it. And so far haven't been hit in the ear with shrapnel. I do wear good polycarb glasses though.

 

[newbury]

Nice post for a zombie thread.

 

[veefre]

Yeah, it's been a while, but it was a good discussion I found via Google.

Anybody ever find cheaper sources for shredder Y-hammers?