When machining with a CNC mill, maximizing efficiency while protecting your machine and tooling is critical. One of the most underutilized yet valuable tools for achieving this balance is the torque chart. The torque chart provides insight into how your CNC mill performs under different spindle loads, helping you fine-tune cutting parameters for optimal results.
To better understand the benefits of using a torque chart, Davie Froeschner, Presales at Tormach, sat down with Tom Zelickman, Tormach Product Manager, to discuss how it can optimize CNC workflows. Tom has extensive experience pushing CNC machines to their limits, and he explains how the torque chart helps machinists get the most out of their equipment.
What Is a Torque Chart, and Why Does It Matter
A torque chart is a reference tool that provides information about a CNC machine’s horsepower, torque, and spindle load at different RPMs. It also indicates how long the machine can sustain a given load before it reaches its limits.
“I use a torque chart as early on in the programming process as I can,” Tom explains. “It helps me decide which tools I want to use, how to set up the machine, and which toolpaths I can leverage to optimize performance.”
The torque chart allows machinists to determine:
- How much material can be removed at a given speed and depth of cut
- The safest and most efficient spindle load levels
- When a machine is being pushed too hard and may require adjustments
Understanding Spindle Load Limits
One of the most important aspects of a torque chart is how it helps manage spindle load. Running a spindle at 100 percent load means the machine can sustain that power indefinitely. However, as you increase the load beyond 100 percent, the machine can only handle it for limited periods. For the 1500MX the torque chart give us the following information:
- 125 percent load – Can run for about an hour
- 150 percent load – Limited to a few minutes
- 175 percent load – Lasts under a minute
- 300 percent load – May only last for 30 seconds
Tom discovered this firsthand during his cut testing. “I pushed my machine to 300 percent spindle load just to see what would happen,” he says. “It was the most elegant failure I’ve ever seen. The machine simply stopped, went into fault mode, and didn’t damage the tool or part. I just had to press reset and jog the tool away from the part before adjusting my parameters.”
How to Use the Torque Chart in Your Workflow Adjusting Width and Depth of Cut
One of the easiest ways to optimize spindle load is by adjusting the width and depth of cut.
“When I was cutting at 300 percent spindle load, I was using a three-eighths-inch cutter with a 50 percent width of cut in an adaptive toolpath,” Tom explains. “That’s a lot. Adaptive toolpaths are meant for 5 to 20 percent engagement. So, I backed it down to 30 percent, then 25 percent, and finally 20 percent, watching the spindle load drop significantly each time.”
The key takeaway is to reduce the width of cut first before reducing depth to maintain an efficient material removal rate.
Managing Feed Rates and RPM
Another important factor in optimizing performance is balancing feed rate and RPM.
- If the spindle load is too high, reduce the feed rate or RPM
- If the machine is underloaded, increase the feed rate to maximize efficiency
“Imagine shoveling snow,” Tom says. “If you take tiny scoops as fast as possible, you’ll waste effort. If you take huge scoops, you’ll burn out quickly. The sweet spot is somewhere in the middle — removing as much as possible at a steady, sustainable pace.”
Recognizing When Adjustments Are Needed
While the torque chart provides a great reference, machinists should also rely on sensory feedback. Here are some common signs that adjustments are needed:
— Sound: A consistent, steady cutting noise is ideal. If the sound changes, it may indicate chatter, rubbing, or improper
speeds and feeds.
— Chip Formation: Well-formed, curling chips indicate efficient cutting. Dust-like chips or excessive heat buildup may
signal issues.
— Load Meter Feedback: The Tormach 1500MX displays a real-time load meter on the screen, allowing machinists to
make adjustments on the fly.
Finding the Ideal Cutting Range
While it might seem logical to always operate in the sweet spot of the torque chart, practical machining factors sometimes require compromises.
For example:
- If a long tool is needed for a deep cut, a lower width of cut might be required to prevent deflection
- If material removal is a priority, adaptive toolpaths help maintain efficient engagement
- Some tools and materials require adjustments based on rigidity, workholding, and tool selection
“This is where machining becomes an art as well as a science,” Tom says. “The torque chart tells you the ideal scenario, but real-world conditions often mean making practical trade-offs.”
Takeaways for Maximizing Machine Performance
Using a torque chart effectively helps machinists optimize cutting performance, extend tool life, and prevent unnecessary wear on their CNC mill. Key takeaways include:
- Use the torque chart early in your workflow to determine optimal cutting parameters
- Adjust width of cut first to reduce spindle load while maintaining material removal rates
- Monitor spindle load and make real-time adjustments using the machine’s load meter if available
- Listen for changes in sound and watch chip formation to detect potential cutting issues
- Understand that practical factors sometimes override theoretical sweet spots
By integrating torque charts into everyday machining, users can push their CNC mills to their full potential while maintaining reliability and precision.
For more details on how to read and apply torque charts, check out our article on torque charts and start optimizing your CNC workflow today.
