shredder design

herbschwabMay 21, 2006

Can anyone tell me the pros and cons of hammermill type shredders, versus serated knives?

Specifically, I'm trying to choose between a Bearcat 70080, with serated knives, and MacKissic LSC510, with hammermill.

I'm trying to make leaf mold and compost by shredding, and chipping branches up to 2" for a wood chip path. I'd say the shredding function is probably most important, to me.


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Chippers: These typically are used to cut pieces of wood into chips of various sizes. "Cut" is the key word. Most chippers have a set of knives mounted on a rotating disk or plate. As the disk rotates, the knives impart a slicing action, cutting the material into small pieces. In a typical landscaping chipper, limbs and branches are sliced piece by piece as they are fed manually through the chamber of the chipper. The pieces that emerge are relatively smooth and evenly shaped particles or chips. Chippers produce premium mulch products because of the relatively uniform shape and size of the chips.

Grinders: Grinders reduce particles in size by repeatedly pounding them into smaller and smaller pieces through a combination of tensile, shear and compressive forces. Nearly all grinders, including tub and horizontal feed grinders, rely on a hammermill as the pounding device. A hammermill has club-like projections - hammers - attached to a rapidly rotating drum (rotor). The high rotational speed (more than 1,000 revolutions per minute (rpm)) gives the hammers enough inertia to shred the material, notes Modern Composting Technologies. As the drum rotates, the hammers spin rapidly and smash against the material trapped inside the hammermill chamber until the pieces are small enough to pass through the discharge screen or grate. To be effective, the material being ground has to be somewhat rigid and brittle, although the hammers will eventually pulverize most anything. Particles coming out of a grinder look ragged, broken and smashed. The particles encompass a wide range of shapes and sizes (smaller than the screen opening).

Shredders: The term shredder is usually reserved for machines that tear particles apart (versus smash). The word "shear" is often added as an adjective, i.e., shear shredder. Compression forces are applied to a particle in offset planes to produce a shearing action. A common shredder in the recycling industry is a low-speed, high-torque shear shredder. This machine uses one or more rotating shafts, each with a set of cutting disks or knives mounted closely together on the shaft(s) that sits in a chamber at the bottom of a feed hopper. As the shaft rotates, the cutting devices pull the material down through the small spaces between the cutting disks/knives and the surrounding chamber. Many shredders use a pair of counter rotating shafts that draw the material down, forcing the pieces out between the two shafts. Particles produced by shredders tend to have an elongated shape.

Help any?

    Bookmark   May 21, 2006 at 11:12PM
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maineman(z5a ME)


Let me point out that the MacKissic LSC510 does not have a hammermill for a shredder. It uses fixed blades which are designed primarily for shredding leaves. The Bearcat 70080 has 12 serrated knives, also designed primarily to shred leaves, twigs, and such.

However, the MacKissic 12PT10 (priced at about $1729) is more comparable to the Bearcat 70080 (priced at about $1699) than is the MacKissic LSC510 (priced at about $959), as you can see from this comparison table in Horticulture Magazine, and the MacKissic 12PT10 does use a hammermill shredder with 24 free-swinging hammers and 1-inch holes in its standard included discharge screen.

The Bearcat and the MacKissic are both good machines, but I chose the MacKissic for several reasons. The Bearcat's blades act by cutting, so their performance degrades as the blade dulls. The MacKissic's hammers act by repeated impact, so they are much less affected by wear and sharpness isn't a worry.

The Bearcat's serrated knives can be reversed once to expose fresh cutting surfaces, while the MacKissic's hammers can be reversed and/or flipped to use all four corners of a hammer. After three years of heavy use I am still using my first set of hammer corners with no problems. The MacKissic's hammers are essentially just pieces of hardened bar stock with pivot holes in each end. Sharpening is not an issue with them. I suspect that it isn't all that easy to sharpen the Bearcat's serrated knives.

Both machines have optional discharge screens, although the MacKissic offers a wider selection and its finest screen has .250" holes while the Bearcat's finest screen has .375" holes. In other words, the MacKissic can produce a much finer textured product, which is of particular value if you are making compost piles or mulch.

Since a hammermill doesn't cut, but pulverizes, you can put things through it that wouldn't respond at all well to knives. I toss in big pieces of old tree bark or pour in acorns and they get pulverized to a fine fluffy material with lots of surface area for rapid composting. The tree bark would tend to jam fixed knives and the acorns would confound them. You can easily run oyster shells through a hammermill, but you wouldn't want to try that with the Bearcat's knives.

I run all sorts of things through my MacKissic's hammermill, like old leafmold riddled with tree roots, all kinds of deadfall, anything I can sweep up with my leaves like twigs, rotten wood pieces, and dirt. Sometimes I recycle a compost pile through it to rescreen it through a finer screen and to really remix it. You probably wouldn't want to be shovelling old compost into the Bearcat's shredder. I considered the Bearcat, but chose the MacKissic for its versatility. And I prefer its four-wheeled wagon design, as well.

The MacKissic can chip 3" versus only 3" on the Bearcat. That's a bigger difference than it sounds like. I also prefer MacKissic's single chipper blade design over the two chipper blades on the Bearcat. The single blade lets the MacKissic make thicker, heftier chips for landscaping use, when you want big chips. For maximum sized chips I simply remove my discharge screen. It goes on and off with no tools required, another handy feature. The MacKissic 12PT10 gives you 10hp versus only 8hp on the Bearcat. I've been using my MacKissic 12PT9 (a 9hp predecessor to the current 12PT10) for three years now, and I really like it.


    Bookmark   May 22, 2006 at 3:16AM
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Thanks, both. Helps lots!

I suppose the serrated knives don't get sharpened at all, just replaced.

It's an expensive machine, either way, and I don't mind spending a few more bucks to buy something of quality that will be used for years.

I'm going to track down a MacKissic dealer, and check out the 12PT10.

    Bookmark   May 22, 2006 at 7:13AM
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maineman(z5a ME)


You can sharpen serrated knife blades. It's just not as easy as sharpening non-serrated blades. My guess is you could use round files of a certain size. Or if the knives are too hardened for a file, you could probably also find a Dremel tool stone that would fit the serrations. Where there's a will, there's a way. The serrated blades probably stay sharp pretty well as long as you just feed leaves to the shredder.

The Bearcats are credible machines. I gave Bearcat serious consideration before I decided I needed something a little different. The serrated knife thing was not a deal breaker for me, although I was partial to the idea of a hammermill, based on my experience with a hammermill on our home farm many long years ago.

I don't even remember its brand name, but we bought it used at an estate auction for $15 (that was a long time ago.) Among other things, we used it to make our own chicken feed out of corn and wheat and we processed corn cobs to make litter for the hens. It had an even wider range of screens than the present day MacKissic 12PT series, going down to some very small screen sizes, some of which we used to make feed for baby chicks, and to downsize oyster shell for them.

Incidentally, I see that Echo has purchased the parent company of Bearcat. I have no idea what the significance of that is, if any.


    Bookmark   May 22, 2006 at 1:37PM
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None of the MacKissic dealers near me have any of the shredders in their shops. Guess they're not big sellers, around here (Chicago suburbs). The 12PT10 sounds like a real workhorse of a machine, but I'm concerned about 1.) its' size. Will take up a lot of space in the shed, 2.) may be overkill for my needs, and 3.) I'm kinda funny about buying an $1800 machine sight unseen.

What you said about the hammermill makes a lot of sense -- we have tons of acorns, and I can see on MacKissics website, that the chipper chute is much wider than the smaller machines, allowing for whole branches to get eaten up in there.

What about the SC763? Does this model have some of the heavy-duty features of the 12PT10, in a smaller package?

    Bookmark   May 22, 2006 at 10:47PM
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Have you even considered something like a DR chipper/shredder?

They are nice because they are both woodchippers and hammermill shredders.

Also, have you considered renting one?

    Bookmark   May 22, 2006 at 11:25PM
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nor_easter(z5 MA)

Organic Herb,

If I may ad another consideration, try to look for a used Kemp chipper/shredder. These were produced in PA, but went out of business in the mid 90's due to increased liability insurance associated with homeowner chipper/shredders. Your can still buy parts for them and they are built to last. I've had mine since 1988 and use it about 15hrs a year and it just keeps taking whatever I throw at it.

    Bookmark   May 23, 2006 at 7:42AM
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maineman(z5a ME)


"What about the SC763? Does this model have some of the heavy-duty features of the 12PT10, in a smaller package?"

The MacKissic SC763 is indeed the least expensive MacKissic model that has a true hammermill shredder. It swings 16 hammers. If I were getting it, I would also buy the optional ½" screen. I would probably use the ½" screen most of the time. On my 12PT9, the ¼" screen gets the most use.


    Bookmark   May 23, 2006 at 12:33PM
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maineman(z5a ME)


The DR CSR180EDR 18hp Chipper/Shredder that you linked to is the "spitting image" of the MacKissic Mighty Mac 16hp SC183-16VE, except for the engine options.

I could be wrong, but I suspect that MacKissic made that machine for DR. I would be curious to see a picture of the 12hp DR CSR120# model, and how it compares to the new MacKissic Mighty Mac SC150-12E & SC150HT-12E models.

The MacKissic SC150 models are designed to fill the gap between the 12PT series and the upscale SC183 "Brute" models, and their prices would put them in a league with the unpictured DR 12hp CSR120E model.


    Bookmark   May 23, 2006 at 1:55PM
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I'd love to buy used, but none available. I'd be happy to rent, too, but only 18 h.p. Vermeer chippers are available in local yards.

I'm starting to like the 12PT10 a lot, 'cause its got bigger chutes than the Bearcat. I like the idea of being able to grind up acorns, and 1" thick bark, too. The only thing is, the wife's gonna hate it, 'cause it's so big! :)

    Bookmark   May 23, 2006 at 9:09PM
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maineman(z5a ME)


"The only thing is, the wife's gonna hate it, 'cause it's so big! :)"

Well, it's not small, but I wouldn't say it is huge, either. Here are some approximate tape measure readings I made today: length: 48 inches (with the tow bar folded back over the rear axle), width 40 inches (including the chipper chute), and height 42 inches. The highest part is obviously the shredder chute.

My work area is down a slope from our garage, so I decided to avoid pulling it up the hill after every use by simply leaving it outside in the work area. I purchased the optional all-weather cover to keep it covered when I am not using it.

To prevent it from "wandering off," I used a bicycle cable to lock it to a tree in the work area. I tied the cover's cinch ropes to the hand towing handle (another option) to prevent the cover from blowing away. We have had a couple of storms with winds exceeding 60mph that probably would have blown the cover away if I hadn't done that. Over the years, high winds have caused significant tree damage here. A lot of dead or weakened limbs were dislodged and several trees were blown down, providing more material for the shredder-chipper. I hope we don't have a serious hurricane here, because the tree damage would be devastating.

Despite all that, the shredder-chipper seems to survive well in the woods under its cover, and starts dependably on the second pull, even when it is cold. This scheme has worked well for me for the last three years. And it's handy having it ready and waiting right at the work site.

I had originally thought I would pull my "Mighty Mac" from one work site to another. But, since a lot of the limbs and brush have to be dragged anyway, it has worked out better for me to leave the shredder-chipper at a central location in the woods and to pull the limbs to it. For convenience, my compost piles are all clustered around that site as well, and that has turned out to be a good location for them, well away from the house. It's not hard wheelbarrowing the finished compost to the garden. I'll be doing some of that tomorrow.


    Bookmark   May 24, 2006 at 11:27PM
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Hey, you answered what was gonna be my next question: Can it be left outside, covered?

If you leave it outside, does it start up o.k. in winter, too? I suppose using straight-weight synthetic oil is the way to go. Also, doesn't the steel housing, chutes, and frame tend to rust, being under a cover?

    Bookmark   May 25, 2006 at 8:17AM
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maineman(z5a ME)


Normally it starts on just the second pull, even in winter. Once, when the temperature got down near zero, I got some ice frozen in the fuel line or fuel filter and it wouldn't start until I warmed it up with a small electric heater on a long extension cord. I would guess I got a little water in the gas. Possibly water vapor condensed in the gas tank. I use regular 87 octane gas, with no additives. The manual recommends against additives. I put the little electric heater on the ground under the cover so the heat would rise in the cover and thaw out the ice, wherever it was. After 30 minutes of that it started on the second pull. In general, it has been very good about starting easily in cold weather. The only thing is, when the machine is real cold, you shouldn't stick your tongue on the metal frame. (grin)

My 12PT9 came with two manuals, one for the Briggs & Stratton engine and one for the MacKissic shredder-chipper. The engine manual has a chart showing to use 30 weight oil from 40°F up to over 100°. For starting in 0° up to 40° it recommends 5W-30 or 10W-30. For operating anywhere from -20° or lower up to 100° or higher it recommends Synthetic 5W-20 or Synthetic 5W-30. To be on the safe side, I have been using Mobile One 5W-30 synthetic oil exclusively. My dealer had installed regular 30 weight oil originally but, after a few hours of "break in" use, I drained that oil and replaced it with the Mobile One. As per the manual, I also retensioned the V-belt after the break-in.

The engines are shipped to the dealers dry, and they install the oil. But double check to make sure your engine has a good oil level before you start it. Starting it without oil would ruin it.

After a few hours of break-in use I think you should drain the original oil and replace it with Mobile One 5W-30 synthetic. That would be my recommendation. In my opinion, it's false economy to skimp on the oil.

You should grease the main rotor bearing initially and after every 10 hours of use. I got a small manual grease gun from Home Depot just for that purpose.

I haven't noticed any undue rusting after 3 years out in the weather. Most everything has a heavy coat of paint on it. Of course, the hammers, mounted screens, and chipping blade are now bare, but relatively frequent use keeps them shining. The unused screens do have some signs of rust, but nothing beyond cosmetic.

I have replaced the paper air filter after it got too hard to clean. It's a standard filter available at Home Depot.

The engine muffler looks rusted. It gets red hot in use. I've used my "Mighty Mac" some at night and you can see the muffler glowing. I always let the machine cool off for several minutes before using the cover, to keep from scorching the cover on the hot muffler. I think the muffler will probably be the next thing that needs replacement. It probably should have been made of stainless steel. But it may go on, looking rusty and glowing, for the next several years.

I have a spare V-belt that I plan to install on my next maintenance session. I have smoked my original V-belt a couple of times, so it's probably due for replacement, but I'll keep it as a spare. It's a little stretched and scorched in a couple of places, but it's still usable in a pinch.

I also bought a chipper knife replacement kit that I plan to use then as well. However, I will keep the original chipper blade and resharpen it for future use.


    Bookmark   May 26, 2006 at 2:18AM
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Well, I finally broke down and bought the 12PT10.

I was fortunate however, to be able to rent a BearCat 70380 before making the decision. One of the dozen-or-so Home Depots in my area happened to have a BearCat in their rental center. It was out of service for about 6 weeks, waiting for replacement blades. This was 2 strikes against it: the serrated blades, and the serviceability. One thing that I did like about the BearCat, though, is that you could disengage the shredding unit with a clutch. This made for easy transport across uneven surfaces without having to shut down the whole machine.

I've only got about 3 hours on the MacKissic, but I'm already happy with my purchase. It definitely handles thicker limbs in the chipper, the chipper chute is bigger, and I'm more confident throwing acorns and tree bark into the shredder. Sometimes it makes scary noises when a chunk of wood is mixed in with the leaves in the shredder section, but I think the hammermill handles it better than serrated knives would.

Thanks for your advice. By the way, I purchased from West Power Tools, and I think that it's the best deal out there, with delivery included in the purchase price. I'll now need to experiment with different screens.

    Bookmark   September 19, 2006 at 9:05AM
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maineman(z5a ME)


Congratulations on your new Mighty Mac! I don't think you'll miss the BearCat's feature that lets you leave the engine running while you transport the machine. My 12PT9 starts on one pull when the engine is warm, and usually just two pulls when the engine is cold. So shutting it off and restarting it is no big deal. And I have found a good spot for it, so I leave the machine in place, under a cover, and drag limbs and big plastic baskets of leaves to it. My compost piles are clustered conveniently near that spot.

West Power Tools gives free shipping on orders over $250. I purchased some optional tine sets for my Merry Tiller from them and added enough stuff (plowbar, plows) to the order to get the free shipping. The extra stuff was, in effect, free.

I use my Mighty Mac mostly in the gardening offseason, which includes pretty much all winter. I dress warmly enough to use it nearly all winter. I change the oil to Mobile One 5w30 for the winter's cold weather running, so my chipping and shredding season is not far off. A big pile of limbs is waiting at my machine now. I like to process dry leaves and brush through a ¼" screen for a fine textured, very compostible product.

Happy chipping and shredding.


    Bookmark   September 19, 2006 at 11:02AM
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I've had my 12PT10 for years now and it just rocks. By the way it is a great nail trimmer if you don't stay focused! Also watch getting your sleave caught on debris when you shove it in the top... I've stalled it twice (but I deserved it). I highly recommend you purchase the following:
1. digital hour meter for service (20 dollars)
2. Oil checker. plastic device that screws into the oil fill hole and you push on the rubber top and it shows the oil level. (10 dollars)

Enjoy the years this unit will give you!

    Bookmark   September 21, 2006 at 1:00PM
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I've thought about a dipstick -- where can I get one? And the hourmeter?

The leaf tamper sounds like it'll save your sleeves and fingernails -- do you have one of these? Or do you just push leaves through the hopper with a stick, like I do?


    Bookmark   October 2, 2006 at 7:19PM
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Regarding the 12PT10 hammer type shredders or any others for that matter.

How good of a job will this one, 12PT10, do with green stuff. I've got mostly tropical palms and plants, so I am mainly concerned with shredding up huge palm fronds, banana leaves and giant bird of paradise leaves.

I've heard of problem with some shredders where they can get clogged when trying to shredd these types of materials.

I don't want to spend half my time unclogging the machine.

Appreciate any advise you may have.


    Bookmark   November 3, 2006 at 6:40PM
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We are looking for a chipper and shredder. Our house sits on 0.93 acre. All you talking about those wonderful equipments seem too big for our yard. I wonder what is best size for our yard. We live in east of Seattle and have a lot of pines, cedars, overgrows. I am wonder in between SC763 and 12PT10. A local store recommended bearcat 70050 for us, but that is very $$$. is any one have similar yard like us?
Thanks in advance for any advices

    Bookmark   April 4, 2008 at 8:45PM
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"I am wonder in between SC763 and 12PT10"
I have a half an acre and an older 7hp model of the 12pt10. The guy next door has a SC763 and has one acre. I simply pull mine behind my tractor while he has to drag his all over the yard. So if pulling a 200lb machine over an acre doesn't bother you get the SC763, it is a great machine. For me, my back and the hill in my yard made the choice. BTW, i found mine used on CR for 300 bucks. Worth its weight in gold.
What ever you get make sure you do the simple maintenance it requires. My neighbor has never sharpened the blade, changed the oil, etc. Last time he was using it, the wood was literally smoking from the blade being so dull. On my suggestion, he tried to change the blade, but gave up and took it to the shop. Cant wait to see the bill on that one....

    Bookmark   April 5, 2008 at 11:02AM
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I've had a bearcat 70080 for a few years. (I have a one acre lot.) It's been renamed SC3305 (I think). I had been advised to get 8hp because 5hp is too weak; so I got an 8. It's heavy; quite a bother to pull around. Maybe I should have gotten the tractor pull option. Good thing I'm a flat-lander.

When it's setup and working well (most of the time) I just love it. When I'm having difficulty I cuss it a lot.

I've broken 3 engine plates. I say that's a defect; the factory says no one else has this problem. It's reasonably easy to replace the motor plate; takes an hour.

The factory says I have too much vibration. Well, yeah; it vibrates and always has. What can you expect from a fire breather like this?

I replace/rotate the knives yearly. They're pretty beat up by then. 8hp chips well even with dull knives. It takes a couple of hours to change the knives.

I really recommend getting a chipper/shredder combination like the 70080; not just a chipper. I'm not familiar with other brands; Bearcat is ok.

    Bookmark   August 28, 2011 at 12:48AM
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Well, here goes... I have had the Mackissic 12PT10 for about 7 or 8 years or so now... I primarily bought this model hoping to shred my crazy jungle full of palm fronds and giant bird of paradise here in So. Cal.

First of all this hammermill chipper/shredder works awesome for any woody type material... it just eats em up without any problems at all.. The circular knife shredder/hopper portion of the unit works awesome for long branches also.

As for wet stuff like palm fronds the hammermill can work fairly well, but you gotta have a system down, otherwise the thing will just get clogged up with a bunch of wet mush. Another problem with palm fronds is that they can wrap around the shaft and bind it up fairly easily... Don't put the fronds in the hopper, it will bind and cause problems.

Steps to keep this thing from clogging or binding..
1. the metal screen that comes with 1 to 2 inch holes is no good for palm fronds and wet materials.. I ended up cutting out the holes so that they were about 3 inches or so with my handy grinder. Bigger holes in the screen is better, but can't just remove screen because the fronds will just shoot out and not get shredded at all, so just use a screen with giant holes. Works waaaay better.

2. It's best not to throw full length palm fronds in the hammermill, it will slow it down.. Recommend cutting them first into 12 or 16 inch lengths first before shredding them.. Same with the giant bird of paradise leaves/stems. Note: recently I have been using an electric lawnmower to shredd my giant bird paradise leaves/stems... it will shredd em so dang fast.. just tilt the lawn mower up and open the side exhaust/bag connection shoot and feed the giant leaves (stems first). Whatever is left at the end can easily be thrown into the 12PT10..

3. Also after a few years, the hammermills do get a bit dull. Just take a cheap carbon fiber grinding disk and sharpen up the edges of each of those small steel hammers.. Doesn't take long. Just remove the screen and you can sharpen them up while they are still mounted on the machine.

My yard has about 50 palm trees and 20 giant birds that I need to tend too myself along with tons of other tropicals, so this 12PT10 has come in real handy for creating my super mulch pile.. Beets putting out 12 or so cans each week overfull of fronds and cuttings.

    Bookmark   November 26, 2012 at 7:13PM
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