Flatness Inspection and On-Site Machining of Swing Bearing Mounting Surfaces on Large Excavators

Excavators and heavy machinery in mining operations rotate their upper structure tens of thousands of times a day on a large bearing assembly known as the swing bearing (slew bearing). The flatness of this bearing’s mounting surface is decisive for the machine’s service life and safety. When the mounting surface loses its level, correcting it requires on-site machining combined with high-precision inspection. This article explains the principles and process of flatness inspection and on-site machining of swing bearing surfaces, followed by a real-world project reference from WCE’s MTE business unit.

What a Swing Bearing (Slew Bearing) Is and Why It Matters

A swing bearing is a large ring-bearing assembly connecting the upper structure (cab/boom) to the lower structure (undercarriage) of an excavator. It carries an enormous load while allowing the upper structure to rotate freely through 360 degrees, making it one of the most heavily loaded points on the machine—and one that must be mounted on a truly flat, level surface.

Why the Mounting Surface Must Be Flat and Level

If the upper and lower mounting surfaces are not flat and level, load and force distribute unevenly across the bearing ring, causing point loading, abnormally fast wear, loosening of mounting bolts, and—in severe cases—premature bearing failure. Keeping flatness within the manufacturer’s tolerance therefore has a direct impact on machine reliability.

Problems Caused by an Out-of-Level Surface

A mounting surface can lose its level through accumulated heavy use, temperature change, impact loads, or structural degradation. Symptoms include stiff or noisy rotation of the upper structure, vibration, loosened or broken bearing bolts, and grease leakage. Measuring and restoring the surface to flat and level is an in-depth maintenance task that extends bearing life and prevents cascading damage.

Flatness Inspection with High-Precision Metrology

Assessing the mounting surface begins with measuring flatness using high-precision instruments such as a dial indicator and 3D coordinate measurement with a CMM/laser tracker, building a surface map that identifies where and how much material must be removed. This accurate measurement data is the basis for planning the machining to achieve specified flatness—and for verifying the result afterward.

What On-Site Machining Is and Why It’s Done in the Field

On-site machining brings portable machining equipment to the job site to turn/face the workpiece in place, without removing large components to a workshop. It suits heavy machinery that is difficult or costly to transport—such as mining excavators—reducing downtime and the risk and cost of transport while maintaining workshop-grade quality.

The Engineering Process, Done Right

The main steps are measuring flatness and the condition of the mounting surface before work begins; installing and setting up the portable machining equipment securely; turning/facing the upper and lower mounting surfaces to the specified level; and re-measuring to verify flatness after completion with CMM/laser tracker before the bearing is reassembled. Keeping the equipment stable and re-measuring systematically is the key to achieving standard-compliant quality in the field.

Standards and Quality Control

Quality on-site machining requires systematic recording of pre- and post-work flatness (an inspection report), the use of calibrated measuring instruments, and work performed to the machine manufacturer’s tolerances—combined with strict safety control in the mine environment—so the results are reliable and traceable.

Project Reference: On-Site Swing Bearing Machining on a PC1250 Excavator by the MTE Business Unit

WCE’s MTE (Machinery Technology and Engineering) business unit carried out a flatness inspection and on-site machining of the swing bearing mounting surfaces of a large Komatsu PC1250 excavator for a major mining operator in Laos, working on-site at the mine.

The team measured flatness with CMM/laser tracker and dial indicator, machined both the upper and lower mounting surfaces with portable equipment, and re-measured to verify the result—all within the scheduled window (8–12 July 2026).

Project Results

• 100% completed as planned
• Upper and lower surfaces machined to specified level on-site
• Verified with CMM/laser tracker before and after work

This project reflects WCE’s readiness to deliver on-site machining and high-precision measurement and inspection in the field—even in mining locations with transport and time constraints.

Contact WCE.

WCE provides on-site machining, CMM/laser-tracker measurement and inspection, and heavy-machinery maintenance in the field, delivered by experienced engineers and technicians—from assessment through handover and after-service support.

📞 Tel: +66 65-937-6283 📧 Email: international@wce.co.th 🌐 Website: www.wce.co.th

We engineer your success.