By Bill Kleiman

The last year we purchased a knife mulcher and have been comparing it to our 15 year old hammer mulcher.  This post is to compare knife vs hammer mulchers for these expensive attachments.  

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 say a stump and stop instantly, causing a lot of stress to the machine.  The ribs keeps 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 when it does get slowed down.  The rotor does slow down when you are cutting.  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. 

Above shows a typical result.  Minimal ground disturbance and small wood chips. 

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 I assume a bit from dirt.   We have had a few teeth get broken from encountering hard objects.  The knives cost about $30 a piece, 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.  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 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 is a bummer.  I mowed into some buried two inch thick steel junk and it tore off the knife, broke the bolt, and bent the holder.   The mulcher has been down ten days now as I wait to get a welding shop to fix it.  The welder will weld some bead here and grind some metal off there, and the bolt hole is in the wrong angle.  I don’t know how they fix the bolt hole.  A mess.  If they can’t fix it then they use a cutting torch and remove the holder and weld in a new one which I have in stock, and hopefully the rotor is still balanced.  I had this happen once to a hammer mulcher, and maybe it won’t happen again, but…so it goes.  Are knife mulchers 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.

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?

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.   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.  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 those hammers instead.
• 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.   We currently are using our hammer mulcher on a tract that has a lot of abandoned metal junk, 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.

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