Optimizing your machining processes is essential for achieving the best performance from your equipment. Among the various factors that contribute to this optimization is understanding how to read and use a spindle motor torque, power, and duration chart. This guide will help you navigate these charts, ensuring you make informed decisions for your machining operations.
The Magical Chart
We all want to get the most out of our equipment, right? There are several factors that help us as machinists to optimize our work. Everything from the material being cut, the tooling used, cutting approach, work holding, and the machine itself contributes to overall performance. Knowing how to read your machine’s “spindle motor chart” is crucial in helping you make good cut path decisions.
What is this magical chart and why is it important? These documents have several names. Some manufacturers call them a horsepower chart. Others might call it a spindle motor graph. Regardless of the naming conventions, it is a chart that displays the motor output information over time. A good chart will show the motor’s rated torque, horsepower, RPM, but most critically the duty cycle at that range.
Let’s examine this simple example chart for the type of information available to us. The lines moving from left to right there are overlaid output lines; one for torque and one for horsepower. Each line represents the output at a specified rated load percentage. The vertical lines on the left and right indicate the rated torque and horsepower; torque level is on the left while the HP levels are read on the right.
Let’s unpack what we see in the real torque chart below (Tormach 1500MX torque and power curves). Each line represents the output (in both horsepower and torque) at the motor’s rated load percentage from 100% up to 300% in varying increments. The color-coded bar on the right also displays the safe duty-cycle for each load.
On this chart, torque is represented by the purple line and stays at maximum output from start until between 6000 and almost 9000 RPM, depending on the load. The green line represents horsepower climbing before flattening out in the higher RPM ranges. The load rating on the far right goes from continuous at that load up to only a brief time.
How it’s measured also makes a difference. The best practice is to measure this data at the spindle since it includes any parasitic losses in the drive train. If the data is measured at the motor, or via a formula and not even tested, you may need to discount the rated horsepower.
Here’s where the magic happens. Now that you know how to read this chart, you can start to plot your cut strategies to attain the best material removal rates. This could be as simple as knowing accurate data to input into feed rate calculators or as complex as you want to make it.
Using the Data
Our first example of how to leverage this understanding is using CAM to program modern, adaptive toolpaths. Sometimes known as trochoidal toolpaths, these cut strategies rely on a lighter width of cut (WOC) with a longer depth of cut (DOC) at fast cutting feeds. Compared to older, classic cut paths which rely on slow and heavy cutting, these toolpaths rely on speed and horsepower rather than torque. Using the data we previously found in our spindle motor power chart, and the cut path example shown below, the calculated cycle time is under 4.5 minutes so the machine can safely operate with a 150% spindle load for the entire duration of this toolpath.
For our second example, let’s take this one step further. You have a cut path that isn’t continuous and the machine rapids back to the start point before entering the cut again. This cooldown period doesn’t reset the timer completely, but it greatly increases the acceptable load for the motor. These micro-breaks result in being able to run the cut at a much higher spindle load for shorter periods of time. Do some testing and measure the amount of time in cut, then use the chart to estimate the true upper limit. You can always keep pushing until you cause a failure, but the chart is here to help guide your decisions and speed your testing process.
For our third example, we will look at how you can use your spindle power chart in conjunction with your tool’s recommended surface footage (SFM) to choose the right tool and gain more efficiency. We can see that the 1500MX makes its most power at higher RPMs. This lends itself to running smaller diameter tools since the operation RPM will be in this higher RPM range. Combined with the 1500’s high cutting feed rates, and the modern adaptive toolpath strategy we discussed in our first example, you get high material removal rates (MRR) with the added benefit of running lower-cost tooling.
Factors That Can Affect Your Results
Electrical input and wiring can cause your results to differ from your predictions. On our spindle power chart, we called out that testing was done with 240V AC. If you are only getting 208V from your provider, you should get a buck-boost transformer such as Tormach pn 32554 to maximize your performance. This simple, cost-effective upgrade can result in up to a 20% boost in performance based on our testing.
Another factor to consider is ambient temperature. When we are measuring the time at a certain load, what we are saying is, “We can run at this load for this time before triggering a thermal overload on the motor.” Make sure to only run your machine in the approved operating temperature ranges.
Tooling matters, though that doesn’t mean you have to buy the most expensive tools to be efficient. Watch for wear on your tool since dull tools exert higher pressure to cut and therefore a higher spindle load. Use the right size and flute number to optimize your spindle RPM and travel feed for your application.
Conclusion
Knowledge is power, so understanding your machine’s strengths will help you get the most out of your setup. Take advantage of modern machining cut paths and size your tools to maximize the spindle rather than trying to take the largest cuts. Spindle motor charts are just one factor in getting the most out of your machine. We also have a variety of educational videos on our YouTube page to help you along the way.
If you have questions about your Tormach machine, you can contact the support team.
