Lumsden Grinding vs. Milling

When specifying the most efficient and accurate manufacturing process for a large, heavy steel component, design engineers face a crucial choice: should the job be handled with Lumsden grinding or CNC milling? Both processes deliver precision, but their strengths differ depending on geometry, material and project requirements.

This article provides a technical breakdown to help you specify the right process for heavy plate work.

What is Lumsden Grinding? (Rotary Surface Grinding)

How a rotating head removes material

Lumsden grinding, also known as rotary surface grinding, uses a large horizontal grinding wheel mounted on a rotating head. The workpiece is held magnetically on a rotary table, and material is removed in sweeping passes across the entire surface.

The rotary action ensures even stock removal, producing flat and parallel surfaces across large, heavy plates.

Key benefits

• Efficiency: Capable of removing several millimetres of material quickly across broad areas.

• Scale: Handles plates weighing several tonnes, making it ideal for base plates, press beds, and machine foundations.

• Economy: Lower cost per mm of stock removal compared with milling when dealing with large surface areas.

What is CNC Milling?

How a cutting tool shapes metal

CNC milling uses computer-controlled cutting tools to machine steel into precise geometries. The tool moves along multiple axes, enabling the creation of slots, holes, profiles and 3D features.

Unlike Lumsden grinding, milling is not limited to flat planes, it’s the go-to process for detailed part geometry.

Key benefits

• Flexibility: Produces intricate pockets, contours and tapped holes.

• Accuracy: Achieves tighter tolerances on detailed features.

• Automation: CNC programming ensures repeatability for batch runs.

When is best to use these processes

For flatness & parallelism on large, simple plates

When your priority is flatness across a large footprint, such as machine bases or structural plates, Lumsden grinding delivers unmatched accuracy and speed.

For complex 3D shapes & features

If the part requires drilled holes, stepped surfaces or intricate cut-outs, CNC milling is the only practical solution.

For speed & cost on bulk stock removal

Removing large amounts of stock from thick plates is faster and more economical with Lumsden grinding compared with milling.

For surface finish & ultra-tight tolerances

In many cases, the most efficient route is Lumsden grinding for bulk removal followed by CNC milling for finishing. This hybrid approach balances speed, cost and accuracy.

Material considerations

S275 & S355 structural steels

Both grinding and milling work effectively. Lumsden grinding is often preferred for heavy plate preparation.

Hardox, Raex and other wear-resistant steels

Lumsden grinding copes well with the hardness when flatness is the main requirement. For shaping features, CNC milling with the correct tooling is essential.

High-carbon or alloy steels

Milling requires specialist cutters, while grinding remains efficient for flat preparation.

Why choose us

Whether you require the bulk efficiency of Lumsden grinding, the precision of CNC milling or a hybrid approach, our team at RMP Products can advise on the most cost-effective and technically suitable route.

Contact us today to discuss your next project and ensure the right process is applied from the start.