For manufacturers producing bolts, anchor bolts, threaded rods, and other fasteners, thread quality is one of the most important indicators of production stability.

Among various thread rolling defects, the wrong thread problem (also called thread overlap, crossed thread marks, or incorrect thread forming) is one of the most serious issues.

If this problem is ignored, it can cause:

• high rejection rates

• unstable thread dimensions

• premature wear of thread rolling dies

• increased production costs

• unexpected machine downtime

This article explains the common causes of wrong thread defects and how to troubleshoot them effectively.

What Is a Wrong Thread Defect in a Thread Rolling Machine?

A wrong thread defect occurs when the thread forming process does not follow the correct helical path.

Instead of forming a clean and continuous thread profile, the workpiece surface may show:

• overlapping thread marks

• double thread traces

• uneven thread entry

• damaged thread profile

This problem is especially common when using:

• three-roll thread rolling machines

• high-pressure hydraulic thread rolling machines

• large-diameter bolt production equipment

Case Study: Thread Overlap Problem During M24 Bolt Production

A fastener manufacturer in Turkey experienced unstable thread quality while producing large M24 bolts on a three-die thread rolling machine.

During production inspection, approximately 3–5 pieces out of every 50 products showed visible overlapping thread marks.

The defect appeared mainly at the thread entrance area, indicating that the workpiece was not entering the rolling dies correctly.

Initially, the operator suspected a damaged thread rolling die.

However, after remote video inspection, the problem was found to be related to three different factors:

1. Thread rolling die synchronization error

2. Workpiece center alignment deviation

3. Excessive hydraulic oil temperature

Main Causes of Wrong Thread Problems

1. Thread Rolling Die Synchronization Error

For three-die thread rolling machines, the position relationship between dies is critical.

During installation or replacement, if the initial positions of the three dies are not synchronized correctly, the forming forces will not be evenly distributed around the workpiece.

Possible Symptoms:

• overlapping thread marks

• uneven thread profile

• increased die vibration

• inconsistent thread pitch

Solution:

Stop the machine and retract the dies.

Use a standard thread gauge or calibration tool between the dies.

Manually rotate the mechanism until all three die teeth engage with the gauge grooves simultaneously.

This ensures that the three dies start forming the thread at the same position.

2. Workpiece Axis Misalignment

The workpiece must enter the rolling dies exactly along the machine centerline.

If the support bracket or center rest height is incorrect, the material may enter at an angle.

This condition is often called:

angled feeding or tilted feeding

Possible Symptoms:

• thread entrance damage

• uneven thread depth

• one side of the thread appearing heavier

• repeated defective products

Solution:

Check and adjust:

• center support height

• workpiece positioning

• die centerline alignment

The recommended alignment accuracy is generally within 0.05 mm for high-quality thread production.

3. Excessive Hydraulic Oil Temperature

Hydraulic thread rolling machines rely on stable hydraulic pressure and cylinder movement.

During long continuous operation, high oil temperature may cause:

• reduced hydraulic oil viscosity

• unstable cylinder movement

• inconsistent feeding speed

• pressure fluctuations

These changes can affect thread forming stability.

Solution:

Install additional cooling equipment when necessary.

For example:

• air-cooled oil cooler

• improved hydraulic tank ventilation

• regular hydraulic oil inspection

Maintaining hydraulic oil temperature below approximately 45°C helps improve machine stability in high-temperature environments.

Step-by-Step Troubleshooting Procedure

Step 1: Check Thread Rolling Die Synchronization

Before adjusting other parameters:

1. Stop the machine

2. Remove pressure from the dies

3. Check die installation position

4. Confirm all dies start forming at the same point

Incorrect synchronization is one of the fastest factors to eliminate.

Step 2: Check Workpiece Center Alignment

Measure the relationship between:

• workpiece center

• die centerline

• support bracket height

Adjust the support system until the workpiece enters the rolling area horizontally.

Step 3: Check Hydraulic System Condition

Inspect:

• hydraulic oil temperature

• hydraulic pressure stability

• cylinder movement speed

• oil cooler performance

A stable hydraulic system ensures consistent rolling force.

How to Prevent Wrong Thread Defects?

Preventive maintenance is more effective than repairing defective products after production.

Recommended procedures:

Regular Machine Inspection

Perform periodic checks on:

• die synchronization

• center support height

• hydraulic oil condition

• spindle and cylinder movement

For heavy production environments, a self-inspection procedure every 10,000 production cycles is recommended.

Monitor Thread Rolling Die Condition

Worn dies can also create thread quality problems.

Check:

• die surface damage

• uneven wear

• abnormal vibration

• reduced thread accuracy

Replacing worn dies before failure helps maintain stable production.

Frequently Asked Questions About Thread Rolling Defects

Q1: Why does my thread rolling machine produce overlapping threads?

The most common reasons include:

• incorrect die synchronization

• workpiece misalignment

• unstable hydraulic movement

• improper machine adjustment

The problem is usually related to setup accuracy rather than major machine failure.

Q2: Can a damaged thread rolling die cause wrong threads?

Yes.

A worn or damaged die can create:

• uneven thread profiles

• poor surface finish

• incorrect thread dimensions

However, operators should also check machine alignment before replacing dies.

Q3: How can I improve thread quality on a rolling machine?

To improve thread quality:

• keep dies correctly synchronized

• maintain accurate workpiece alignment

• control hydraulic oil temperature

• inspect machine settings regularly

Stable machine adjustment is essential for consistent bolt production.

Q4: Are wrong threads common in three-roll thread rolling machines?

Three-roll thread rolling machines provide high production efficiency, but they require precise setup.

Incorrect installation, poor alignment, or improper maintenance can lead to thread defects.

Regular calibration helps prevent these problems.

Conclusion

Wrong thread defects in thread rolling machines are usually caused by setup errors, alignment problems, or unstable operating conditions.

Before replacing expensive thread rolling dies, manufacturers should first check:

1. Die synchronization

2. Workpiece center alignment

3. Hydraulic system stability

With proper adjustment and preventive maintenance, thread rolling machines can maintain stable production quality and significantly reduce defective products.

For bolt manufacturers, a precise setup process is one of the most effective ways to protect tooling life and improve production efficiency.