Knives are the cheapest part of the mixer that cost you the most money when they’re worn. Dull knives don’t stop the mixer. They just make every load take longer, burn more fuel and turn out a worse ration. Most guys run them way past done.
Signs your knives are worn
- Mix time is creeping up. Same ration, same load, longer to process hay.
- Hay comes out in long strands or mats instead of cut pieces.
- The tractor is working harder on the same loads.
- The edge is rounded, chipped or mushroomed when you look.
- Serrations are gone on serrated knives.
- Particle test results changed without a ration change.
Why it costs money
Every extra minute of mix time is fuel and labor, every load, every day. And when forage isn’t cut, cows sort. Sorting means some animals get too much grain and some too little.
In dry years, hay quality drops and processing gets harder. We wrote about how drought hay turns process time into a real cost. Sharp knives matter even more then.
How often to change them
There’s no fixed number. It depends on how much long forage you process, how abrasive it is, and whether there’s dirt or stones in the bales. Check weekly, and track mix time. When it creeps, look at the knives.
Many operators rotate knife positions to even out wear, then replace in sets.
Changing knives safely
- Shut off the tractor, take out the key, and disengage the PTO.
- Lock out so nobody can start it.
- Wear cut-resistant gloves.
- Clean around the knife bolts before loosening.
- Replace hardware if it’s worn, and torque to spec.
Different knife types
- Smooth knives: clean cut, often for drier forage.
- Serrated knives: grip and cut tough or wet material.
- Different lengths and positions: change how aggressive the cut is.
Some farmers mix knife types on the auger to suit their ration. Ask your dealer what works for your forage.
Sharpening vs replacing
Some knives can be sharpened. It saves money but takes time, and the edge may not last as long as a new one. If you sharpen, keep the original angle and don’t overheat the steel.
Many operators find replacing is quicker and gives a better result, especially with modular systems.
Knife position matters
Knives at different heights on the auger do different jobs. Lower knives often do more cutting. Rotating knife positions can even out wear.
Counter-knives and restrictors
Counter-knives on the tub wall work with auger knives to cut forage. They wear too. Check them when you check auger knives.
Tracking knife life
Write down when you change knives and how many loads they did. Over time you’ll know how long they last on your ration. Then you can plan changes before they slow you down.
The real cost of dull knives
Longer mix times mean more fuel, more tractor hours, more labour and more wear on the gearbox. Worse particle size means more sorting. Add it up and a set of knives looks cheap.
Ordering knives ahead
Keep a full set of knives and bolts on the shelf. Waiting for parts while knives are dull costs you every day. Order the next set when you fit the spare. Check bolts and holders when you swap knives, because a worn holder won’t hold a new knife at the right angle. Use the torque figure in the manual and recheck after the first few loads.
Quick questions
Can I mix new and old knives? You can, but the new ones do most of the work. Replace sets where possible.
Do serrated knives last longer? It depends on the ration. Track loads per set and you’ll know for your farm.
What’s the first sign knives are going? Mix times creeping up on the same ration.
One more thing to ask
When you buy a mixer, ask the dealer for the knife part numbers, the price of a full set and how many they keep on the shelf. Ask whether different knife styles are available for your forage. Write it on the inside of the shed door. When a knife breaks on a Saturday, you’ll be glad you know exactly what to ask for and where to get it. Farmers who plan knife changes spend less on fuel and gearbox repairs. It’s one of the cheapest habits on the farm.
Making it quicker
If knife changes take forever, they get skipped. That’s why we built the V2 modular knife system, so swaps are fast and you replace only what’s worn.
Bottom line? A set of knives costs less than a month of extra fuel and slower loads. Keep a spare set on the shelf.
Learn more about LEO Agriculture and our full line of feed mixers and manure spreaders.
