High Speed Machining: What It Is & How To Use It

High-speed machining is a process that achieves high metal removal rates by using lighter cutting passes in combination with elevated spindle speeds and feed rates.

This technique offers several advantages—it significantly reduces cycle times, extends the lifespan of cutting tools, and enhances overall shop productivity.

If you're planning to implement high-speed machining in your operations, here are a few key factors to consider.

What Is High-Speed Machining?

The concept of high-speed machining (HSM) dates back to the 1920s, when German inventor Dr. Carl Salmon discovered that the peak heat generation at the tool-workpiece interface occurred at a specific critical spindle speed, depending on the material being machined. This groundbreaking insight laid the foundation for the development of high-speed machining techniques.

High-speed machining involves making rapid, low-pressure, and shallow cuts. It is particularly effective for producing complex mold geometries and precision structural components—especially in industries like aerospace. The technique's hallmark is its ability to achieve high material removal rates, primarily due to the speed and efficiency of the cutting process.

Is It Beneficial?

Absolutely. High-speed machining provides several compelling advantages—chief among them is increased equipment longevity. Because the process uses lighter cutting loads at higher speeds and feed rates, both the machine and cutting tools experience significantly less mechanical stress.

Additionally, the rapid material removal reduces heat buildup, which minimizes heat transfer to the workpiece. This not only lowers cooling requirements but also shortens cycle times. As a result, shops benefit from faster turnaround, improved energy efficiency, and reduced emissions.

Performing High-Speed Machining

High-speed machining (HSM) encompasses a collection of advanced techniques applied across a wide range of manufacturing operations. These methods are straightforward to implement and can significantly improve machining efficiency and part quality.

Below are some of the most effective HSM techniques:

1. Milling and Trochoidal Machining
This CNC milling method is ideal for cutting deep recesses, narrow cavities, and grooves. Trochoidal machining excels at slotting through tough materials such as titanium and Inconel.

Key benefits of trochoidal machining include:

• Reduced cycle time

• Compatibility with multi-fluted cutting tools

• Increased material removal rates

• Extended tool life

• Beneficial chip thinning effects

• Fewer required axial passes

• High-speed operation capability

• Consistent feed rates throughout the cut

2. Plunge Roughing
Plunge roughing is a CAM toolpath strategy, often manually programmed, that is highly effective for roughing operations. It's particularly useful for older machines or deep pocketing tasks where tool deflection is a concern.

Core characteristics of plunge roughing:

• Shifts cutting forces from the X-Y plane to the Z-axis, allowing for more rigid and stable cutting

• Uses helical drills to remove more material than standard end mills

• Ideal for deep cavities or pockets that would cause deflection in traditional roughing

3. Step-Over Transitions ("Steps to the Side")
This technique involves transitioning between adjacent toolpaths at high feed rates, often using tight-radius stepover moves. It allows for sharper, more efficient transitions between passes—especially useful in surface finishing.

• Enables smooth movement between scan lines in surface machining

• Reduces slowdowns at direction changes

• Frequently used in finishing multi-surface models with parallel scanning patterns

• Incorporating looping or rounded paths can enhance flow and maintain speed during complex transitions

Configuration Tips for CNC High-Speed Machining

High-speed CNC machining plays a critical role in modern machining services due to its ability to quickly and accurately produce parts, significantly boosting production efficiency. Compared to conventional machining centers, high-speed CNC systems differ in several core components, including spindles, tool magazines, tooling materials, and control systems. Among these, the most significant differences lie in spindle speed and cutting feed rate.

1. CNC Machining Centers with High-Speed Feed Cutting

In high-speed machining, increasing the cutting feed rate directly improves machining efficiency. High-speed CNC machining centers typically operate with feed rates between 20–40 m/min, delivering faster material removal and shorter cycle times.

The advancement of linear motors has revolutionized high-speed CNC technology. Unlike traditional ball screws, linear motors offer non-contact direct drive, resulting in:

• Minimal mechanical wear

• No backlash or distortion

• Superior precision

• Exceptionally fast acceleration (up to 2g)

• Feed speeds 4–5 times faster than conventional systems

This leap in drive technology enhances both productivity and machining accuracy.

2. Specialized Spindles for High-Speed Machining

A high-speed CNC machining center requires a spindle that offers:

• High rotational speed (typically 10,000 rpm or higher)

• Excellent rigidity

• Low thermal deformation

• Smooth and stable operation

There are four main spindle types:

• Belt-driven

• Gear-driven

• Direct-drive

• Electric spindles

Among these, direct-drive and electric spindles are the only viable options for true high-speed machining. While direct-drive spindles offer greater cutting force, electric spindles support higher maximum speeds. The choice depends on whether speed or torque is more critical for the intended application.

3. Tooling for High-Speed CNC Machining

Tool selection in high-speed machining focuses not just on tool type but primarily on tool material. Common materials include:

• Polycrystalline diamond (PCD)

• Cubic boron nitride (CBN)

• Hard-coated carbide tools

These materials can withstand extreme cutting speeds and help maintain tool life under intense thermal and mechanical stress.

Dynamic balance becomes essential at high rotational speeds, especially for tools with extended shanks. Poor balance can lead to:

• Excessive vibration

• Tool breakage

• Operator safety hazards

Additionally, the tool holder system affects performance. A 7:24 taper, single-sided clamping holder is most commonly used due to its high repeatability in automatic tool changes and strong clamping force.

4. CNC System Requirements for High-Speed Machining

High-speed CNC machining demands a more advanced control system than standard setups. The CNC system must offer:

• High-speed data processing

• Multi-axis synchronization (4 or 5 axes)

• Superior interpolation accuracy

• Smooth, real-time path control

Using 32-bit or 64-bit processors is highly recommended, as they provide vastly greater computing power than conventional controllers—ensuring stable performance, even under complex, high-speed machining conditions.

CNC Programming for High-Speed Machining Centers

Programming for high-speed machining (HSM) differs significantly from conventional CNC programming. Due to the high feed rates and spindle speeds involved, programmers must carefully anticipate the tool path and cutting behavior to maintain precision, tool integrity, and surface quality.

1. Avoid Abrupt Direction Changes

In high-speed machining, abrupt changes in tool direction can lead to:

• Reduced cutting speed

• “Crawling” (hesitation or jerking motion)

• Poor surface finish

• Tool or spindle damage

• Overcutting or uncut residuals

To prevent these issues, programmers should favor smooth transitions and gentle curves in the tool path over sharp directional changes. Small feeds and shallow depths of cut should be maintained throughout the operation.

2. Intelligent Handling of 3D Contours

When programming complex 3D surfaces:

• Treat difficult areas (tight corners or fine features) separately from general contours

• Avoid basic “zigzag” or straight-line strategies for complex profiles

• Instead, use continuous surface processing methods for greater consistency and accuracy

3. Optimize Entry and Exit Paths

Tool entry and re-entry strategies are crucial in HSM:

• Use gradual tool engagement when entering the material

• Avoid abrupt re-entry after cutting out; instead, re-enter gradually at the same layer

• Prevent tool load spikes, which cause deflection and reduce surface quality and tool life

4. Maintain Consistent Cutting Conditions

One of the key principles in HSM is constant tool load. This requires:

• Uniform cutting thickness

• Stable feed rates

• Consistent cutting speeds

Fluctuations in these parameters can lead to tool deflection, reduced accuracy, and early tool wear.

5. Pre-Process Critical Areas

Pre-machining certain regions of a part—especially where small-diameter tools are required—can:

• Minimize load variations between roughing and finishing

• Reduce unnecessary tool passes

• Improve finishing accuracy and reduce tool wear

6. Use CAM Software Features Effectively

Modern CAM systems offer features specifically designed for high-speed machining:

• Processing residue analysis: Identifies uncut areas after each pass for targeted cleanup

• Tool path optimization: Automatically adjusts feed rates and smooths transitions

• Overcut control: Prevents damage to the part and tool from excessive cutting

• Feedrate control algorithms: Maintain the maximum safe feedrate across dense toolpaths

• Arc transitions: Smoothly link straight segments using arcs to reduce acceleration/deceleration cycles

7. Toolpath Verification and Optimization

Before sending the NC code to the shop floor:

• Use simulation and verification tools to check toolpaths for errors or inefficiencies

• Leverage software features that automatically adjust feedrates to maximize efficiency and safety

• Ensure the digital model of the workpiece is accurate and supports continuous, unbroken machining paths