Why Is My Machine’s Cut Length Drifting Over Time?

You are dealing with measurement drift, not a simple offset error.

If your cut length starts accurate but gradually becomes:

• Longer

• Shorter

• Increasingly inconsistent

You are dealing with measurement drift, not a simple offset error.

The most common causes are:

• 1️⃣ Encoder wheel slippage
• 2️⃣ Strip tension changes during run
• 3️⃣ Coil diameter reduction effects
• 4️⃣ Hydraulic timing variation
• 5️⃣ Heat-related mechanical expansion
• 6️⃣ Pinch roller wear
• 7️⃣ PLC scaling miscalibration

Let’s break it down properly.

1. Encoder Wheel Slipping (Most Common Cause)

Encoders measure strip movement.

If the encoder wheel:

• Slightly slips on coated material

• Loses grip over time

• Becomes oily

• Wears down

Measurement becomes progressively inaccurate.

Symptoms:

• First few parts correct

• Drift increases gradually

• Worse at higher speed

Fix:

• ✔ Clean encoder wheel
• ✔ Increase contact pressure
• ✔ Inspect rubber coating
• ✔ Replace worn encoder wheel

Small slip over long runs causes noticeable drift.

2. Strip Tension Changing During Production

As coil diameter reduces:

• Rotational inertia changes

• Brake tension changes

• Strip tension fluctuates

Tension changes cause:

• Slight material stretch variation

• Measurement drift

Fix:

• ✔ Adjust brake as coil empties
• ✔ Stabilize loop control
• ✔ Monitor strip tension actively

Tension stability is critical for length accuracy.

3. Pinch Roller Wear or Slippage

If pinch rollers lose grip gradually:

• Strip movement becomes inconsistent

• Encoder measurement becomes inaccurate

Signs:

• Drift increases over long runs

• Surface of roller becomes smooth

Fix:

• ✔ Inspect roller surface
• ✔ Clean rollers
• ✔ Adjust pressure
• ✔ Replace worn rollers

Feed stability must remain constant.

4. Hydraulic Shear Response Drift

Hydraulic systems can drift due to:

• Oil temperature rise

• Valve response change

• Pressure variation

As oil warms:

• Reaction time changes

• Shear activation delay shifts

Symptoms:

• Drift worse after long production

• Accurate at startup

Fix:

• ✔ Check oil temperature
• ✔ Verify pressure stability
• ✔ Adjust PLC delay compensation

Hydraulic timing changes with heat.

5. Thermal Expansion in Machine Components

During long production runs:

• Shafts expand slightly

• Frame expands

• Shear position shifts minutely

Though small, these changes can affect precision.

More common in high-speed production.

6. PLC Scaling or Calibration Error

If encoder scaling factor is slightly incorrect:

• Small error per meter

• Multiplies over longer distances

Example:
0.2mm error per meter = 2mm drift over 10 meters.

Fix:

• ✔ Perform full encoder calibration
• ✔ Measure actual vs commanded length
• ✔ Adjust scaling factor precisely

Precision scaling prevents cumulative drift.

7. Flying Shear Synchronization Drift (If Applicable)

In flying systems:

• Servo tuning may drift

• Encoder sync may shift

• Position offset may accumulate

Drift often worse at high speeds.

Recalibration required.

8. Coil Core Slippage

If coil slips slightly on mandrel:

• Strip speed fluctuates

• Measurement reference shifts

Often gradual and subtle.

9. Electrical Signal Noise

Interference from:

• VFDs

• Motors

• Poor grounding

Can distort encoder signal over time.

Fix:

• ✔ Inspect shielding
• ✔ Separate power and signal cables
• ✔ Improve grounding

Signal integrity matters.

10. Pattern Recognition Guide

Drift Pattern	Likely Cause
Gradually longer cuts	Encoder slip
Gradually shorter cuts	Hydraulic delay shift
Drift only after 30+ minutes	Heat-related issue
Drift worse at high speed	Timing compensation error
Drift increases as coil empties	Tension imbalance

Understanding pattern simplifies diagnosis.

11. Step-by-Step Drift Diagnosis

If cut length is drifting:

1. Measure first part and log length

2. Measure after 10–20 parts

3. Compare trend (increasing or decreasing)

4. Inspect encoder contact

5. Clean measurement wheel

6. Check strip tension

7. Monitor hydraulic temperature

8. Perform scaling recalibration

Adjust only one system at a time.

12. Why Drift Is Dangerous

Length drift can cause:

• Assembly mismatch

• Structural tolerance failure

• Batch rejection

• Installation delays

• Increased scrap

Small drift compounds quickly.

Final Expert Insight

Cut length drifting over time is usually caused by:

• ✔ Encoder slippage
• ✔ Strip tension changes
• ✔ Pinch roller wear
• ✔ Hydraulic timing variation
• ✔ Thermal expansion
• ✔ Calibration scaling error

The most common cause is encoder-related slip combined with changing strip tension.

Stable length accuracy requires:

Stable feed → Accurate measurement → Consistent tension → Controlled timing → Proper calibration.

When those systems are stable, drift disappears.