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Reader Question: As we shop for equipment, we’re doing the typical spreadsheet exercise comparing baseline specs. Our research leaves us hanging, however, because all these machines seem to have the same max rapid traverse rate. Can you explain this and how we might differentiate the machines in front of us?

Coming from the machine tool world, I always appreciated a prospective buyer who tried to “look past the spreadsheet.” That mindset was practically a mantra during my years involved with premium machines. But while it sounds great in theory, it’s often harder to put into practice. Most buyers start with a spreadsheet full of baseline specs: rapid traverse rates, spindle rpms, tool change times. These figures are useful for comparison, but only up to a point. What gets lost in this approach is the real-world behavior of machines and how performance changes based on use case. Two machines may show identical rapid traverse rates yet deliver vastly different results on your shop floor. Why? Because true machine speed is more nuanced than a number on a spec sheet.

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What Does “Speed” Really Mean?

Machine speed, like vehicle performance, is not always straightforward. Most people intuitively understand what 0–60 mph or top speed means for a car, but even then, context matters. That top speed may not hold if you’re towing a trailer or accelerating uphill. Similarly, a machine’s advertised rapid speed may never be reached in actual operation, depending on part geometry, travel distances and code complexity. In practice, the speed that truly matters is the speed at which your machine can complete a cycle — cutting, positioning, changing tools and everything in between. The key question isn’t how fast the machine can go, but how fast it will go in your environment, running your parts.

Understanding Machine Specs

Machine speed is typically characterized by two headline specs: maximum rapid traverse and acceleration. Max rapid traverse is the top speed at which the machine moves between points when not cutting. Acceleration is how fast it reaches that max speed — often shown in Gs, where 1G equals the force of gravity (9.8 m/s²). While these numbers can be helpful, they’re not the full story. A machine’s rapid speed only helps if it has time to reach it — something that rarely happens on short-stroke moves. That’s why acceleration — and more importantly, how quickly a machine begins to accelerate — is just as critical.

Acceleration Surge

There’s an often-overlooked characteristic called acceleration surge — essentially, how fast a machine gets moving from a standstill. Think of it like a football player’s first step off the line. Even with a lower top speed, a machine that gets off the line quickly can outperform others in typical cycle work. Many premium machines feature smoother acceleration curves that favor stability, while high-production machines may be tuned for explosive starts and stops. It’s worth noting that some machines with slightly slower top speeds may complete a given move faster because of this surge. The only way to know is through real testing.

Tool Change Time vs. Chip-to-Chip Time

Tool change time is often clearly listed, but chip-to-chip time is the more telling metric. It includes everything from the machine’s axis movement to the tool changer, the actual tool swap, spindle ramp-up or ramp-down and repositioning. This gives a better sense of machine responsiveness across tool changes. However, chip-to-chip time isn’t always tested consistently across brands. Was the test done at full spindle rpm or half? Did it include ramp-up and ramp-down? Was the stroke full, partial or minimized? These things matter — and they can skew how meaningful those numbers are to your process. Depending on your shop, this metric could be critical — or barely relevant. For example, if you run long cycle times with minimal tool changes, the difference between three and four  seconds of chip-to-chip time may not matter. But if you’re making hundreds of small aluminum parts per day, those seconds add up quickly.

Code Execution and Real Performance

Beyond mechanical speed, a machine’s control system plays a big role in how quickly and accurately it runs programs. This includes features like look-ahead, block processing rates and the controller’s ability to maintain speed on complex geometries. Don’t mistake high rapid speeds or G ratings as a guarantee of fast part production — especially for complex 3D surfacing or tight radius work. Code-heavy programs demand fast processors and smart motion control. Two machines with similar mechanical specs may differ dramatically in how well they hold accuracy and finish at high speed. For example, a machine might blaze through a part in air but stutter during cutting due to limited look-ahead or processor lag. Fast hardware paired with slow software won’t give you the throughput you’re looking for.

Putting This to the Test

One message I return to often in this column: when in doubt, test it out. A test cut — or at the very least, a dry run — can tell you far more than a spreadsheet ever will. Develop a simple program that reflects your actual workflow. Include some repositioning, tool changes and surfacing if applicable. Then send that same program to each machine builder and ask for a timed demo. If you’re primarily running medical parts, your demo might include surfacing and tight corners, putting the control system and look-ahead to the test. If you do heavy machining on iron, your focus may be more on stability, torque and rigidity. For shops with high-volume aluminum work, rapid traverse and tool change behavior are key. Even a dry run — no cutting involved — can give you a measurable performance comparison in terms of actual cycle time. From there, you can balance what you see with your other priorities: price, service, footprint, options and so on.

Machine speed is complex. While spec sheets give you a starting point, they often mask deeper performance differences. Acceleration surge, control processing, real-world cycle times — all of these contribute to a machine’s actual speed in your shop. So yes, look past the spreadsheet, but more importantly, look at the machine in motion. That’s where the numbers stop, and the insights begin.

Do you have a machining question? Ask the expert. John Miller leans on more than a decade of industry experience to answer machining questions from MMS readers. Submit your question online at .