Why Your Wood Pellet Mill Feeds Unevenly from Both Sides (And How to Restore Balance)

When your wood pellet mill starts producing pellets from only one side of the die, or one side clearly outputs more than the other, it's more than a minor quirk. This uneven discharge is a critical symptom of imbalance within your machine. Ignoring it leads to reduced overall capacity, accelerated and uneven wear on expensive components like the die and rollers, and ultimately, costly unplanned downtime. The core of the problem almost always revolves around an unequal distribution of force or material.

Think of the pelletizing chamber as an ecosystem that needs perfect equilibrium. When pressure, material flow, or mechanical alignment is off-center, the system forces the path of least resistance—resulting in one side of the die doing all the work while the other underperforms. Let's diagnose the common culprits behind this frustrating issue.

The Primary Suspect: Uneven Material Distribution
Before blaming the mechanics, check the most straightforward cause: is material reaching both sides of the die equally? The design of the feed hopper, the condition of the internal feed paddles or plows, and even the rotation of the die itself can cause material to channel or "race" to one side.

If internal feed chutes are worn or angled incorrectly, or if centrifugal force during die rotation isn't properly managed, one side of the chamber becomes overfilled while the other is starved. An overfilled side creates excessive pressure and may even jam, while the underfilled side lacks the necessary material to form pellets consistently. The fix often involves inspecting and adjusting or replacing these internal feed components to ensure a uniform "blanket" of material covers the entire die face.

Pressure Imbalance: The Roller-Die Relationship
The heart of pellet formation is the precise gap and pressure between the rollers and the die. If this force is not equal across the width of the machine, uneven production is guaranteed.

This imbalance can stem from several mechanical issues. On a ring die machine, if the rollers are not perfectly centered within the die ring, or if the bearings on one roller are worn more than the other, the applied pressure becomes lopsided. On a flat die machine, if the roller assembly is not level, the same problem occurs. Furthermore, a die that is itself slightly warped or out-of-round—a condition that can develop over time under heat and stress—will inherently create inconsistent contact with the rollers. This forces one side to work harder while the other disengages.

A Hidden Culprit: The Worn or Misaligned Main Shaft
Through years of field service and client support, we've identified another, less obvious cause that can baffle operators: a worn or improperly installed main shaft bearing assembly.

Over very long periods of high-load operation, the main shaft bearings can wear unevenly. More critically, when these bearings are replaced, if the bearing housing is not precisely realigned, the main shaft can develop a slight rotational eccentricity. This means the core of your pellet mill—the shaft driving the die or rollers—is no longer spinning perfectly true. This fundamental imbalance transmits uneven forces throughout the entire compression chamber, making it mechanically impossible for both sides of the die to work uniformly, regardless of other adjustments. This issue requires a thorough mechanical inspection by a qualified technician.

Diagnosis and Action: A Systematic Approach
Fixing uneven discharge requires a logical, step-by-step process:

Start with the Feed. Visually inspect (with the machine safely off and locked out) the internal feed system for wear, damage, or obvious bias. Ensure a uniform feedstock is being used.

Inspect the Die and Rollers. Look for signs of uneven wear patterns on the die surface and the rollers. Check the roller gap with a feeler gauge at multiple points to verify it's consistent.

Listen and Feel. During operation, unusual noises or vibrations from one side of the machine can point to bearing wear or alignment issues.

Consider Mechanical History. If the problem arose after recent major service (like a bearing change), the possibility of a misaligned shaft or housing must be investigated.

Restoring Harmony for Peak Performance
An unevenly discharging pellet mill is a machine crying out for correction. It's a clear sign that the critical balance between force, flow, and alignment has been lost. By methodically investigating material distribution, roller-die pressure, and core mechanical integrity, you can identify the root cause. Addressing it not only restores balanced production and protects your capital investment but also ensures your operation runs at its designed, efficient potential. Consistent output from the entire die face is the hallmark of a healthy, well-maintained pellet mill.