By Bill Kleiman

Updated March 2026. We are on our second winter using a knife mulcher.   

Link to a 2 minute time lapse video of a hammer mulcher clearing small brush to show off a treasure: https://youtu.be/6SrNRwR49tY

Above is a Cat 110 horsepower 299 D3XE skid steer we use with a new Denis Cimaf DAF-180D brand knife mulcher.   You can see some of the 27 knives there which are bolted to the rotor.  Note the thick ribs that go around the rotor.  The ribs keep the knives from grabbing too much of a bite of the wood.  Like on a chainsaw chain the rakers in front of the cutters keep the knives from grabbing the wood and stopping the saw abruptly (which leads to kickback in the case of a chainsaw).  Without the ribs the knives would grab a stump and stop instantly, causing a lot of stress to the machine.  The ribs keep the rotor spinning fast so the knives can slice off wood in bite-sized pieces.  The dealer claims the hydraulic motor that spins the rotor is also well designed to spin fast and recover its speed (spool up) when it does get slowed down.  For sure, the rotor does slow down when you are cutting heavies.  There is a limit to the magic.

Above shows a brand new knife and a partially worn knife.  We tend to sharpen our knives about every 8 hours of cutting. Typically, every morning we sharpen knives even if the day before we only mowed 4 hours.

Above is knife needing some sharpening

Above is that knife sharpened. You want to take metal off that entire surface to keep the cutting angle just right.

Above, the result of mowing into metal junk. Stay back from fence rows with the knives.

Above shows a typical result of a knife mulcher.  Minimal ground disturbance due to the wide rubber tracks and small wood chips. Keeping the knives above the soil keeps their sharpness longer.

Above, the knife mulcher makes a fine mulch.  The knives can clear more habitat because of this clean cutting.  This style mulcher cuts very fast. It also looks tidy.

Above is a brand new knife and a very worn down knife.  There is a day and night difference in the performance of a sharp vs a dull knife, similar to a chainsaw chain.  The knives are dulled by rocks, fence posts, and sandy soils.   We have had a few teeth get broken from encountering hard objects.  The knives currently cost about $60 a piece! To replace the entire set of knives, and their nut and bolts will set you back about $1,800. So you want to sharpen them until they are used up.

Above I am sharpening knives using the sharpener supplied with the purchase of the mulcher.  This sharpener has a powerful two stroke motor that is spinning a 3M brand of very course sand paper.  The sanding paper disc lasts a long time, unless you bump into an unexpected edge and the $10 grinder paper tears. Sigh. 

The teeth can be sharpened in about 15 to 20 minutes.   The sharpener is loud and we leave the shop door open to vent the shop.  We also grease the zerks and do other work on the skid loader. 

Above shows my tools splayed out as I change a bunch of worn out knives.  The nuts are held on with 400 hundred pounds delivered by a large torque wrench. To get the bolts loose it takes a breaker bar and 4 foot extension tube and your body weight.  Once loose, then you can switch to the cordless nut driver.  This Denis Cimaf mulcher came with clear instructions and a kit of tools needed.  The teeth can last for a few to several months, or a few can be trashed on the first junk you run into.

Above shows a damaged tool holder, the part that holds the knife.  This damage is a bummer.  I mowed into some buried two inch thick steel plate and it broke the bolt that holds the knife, tore off the knife, and bent the holder.   We carefully ground the holder to get it to continue holding a knife. If it was a bit more damaged then a welding shop will use a cutting torch and remove the holder and weld in a new one, and hopefully the rotor is still balanced.  I had this procedure done once on a hammer mulcher.  Is this model prone to this damage?  Could be.

Hammer Mulcher:

Above is hammer style brush mulcher.  Those hammers are tipped with carbide, the twin V you see on the ends.  This design can take a lot of punishment from hitting rocks and abandoned junk.  This is a big advantage to this hammer style. No sharpening is involved.

Using the hammer mulcher I mowed this abandoned implement.  The hammers showed no damage but I tore this junk in several pieces.   Would the knife mulcher take this abuse? Nope.

Above is a fence post mowed into pieces by the hammer mulcher.   No harm done.

Above, the hammer mulcher leaves a bit more of a rough mulch. The hammer mulcher takes longer to mulch trees.  If you are mowing heavy brush the knife mulcher is noticeably more productive. Mowing shrubs is about the same with either mulcher.

Bottom line advice on knife vs hammer mulchers:

• Both are expensive.
• The hammer mulcher is good for sites with rocks and abandoned junk.
• The knife mulcher is very productive, cutting through wood much faster.
• The knife mulcher needs sharpening every 8 hours or so, and knives replaced at times, and the entire set of expensive knives replaced at least annually.   Do you have a shop to get out of the weather to do this?  You can tough it outside, but you might be wishing you had bought a hammer mulcher.
• Don’t trade in your old hammer mulcher.  We have a 15 year old Fecon and it is built to last for a long time.  Check the belt drive annually, clean out the belly of it.  We currently are using our hammer mulcher on a tract that has a lot of abandoned metal junk, and it does quite well on brush and trees, and we will use the knife mulcher when we get to cleaner ground.

Above, knife mulcher is clearing invasive honeysuckle and small trees from an oak savanna.  Note minimal ground disturbance.

This is the link I started this post with. It is a 2 minute time lapse video of a hammer mulcher clearing small brush to show off a treasure. People enjoy time lapse: https://youtu.be/6SrNRwR49tY

End.