When it comes to CNC machine tools, it’s hard to argue there’s a more important component than the spindle. Yes, the computer portion is key, but without the precision rotation of the spindle, there is no cutting, milling, grinding, or routing of precision products that such machine tools are known for and are expected to deliver. Without a reliable spindle, you effectively have a failed CNC machine tool.
So, to ensure your spindle is performing as it’s designed to, it’s critical to execute required spindle maintenance and take corrective actions when necessary to ensure your spindle meets its required performance standards. Below, we’ll get into the various ways you should test and maintain your spindle to get the most accurate and reliable performance without sacrificing quality and precision in your final products.
Inspect the Spindle Lubrication System
As a rotating tool that’s heavily involved in the manufacturing and machining of precision parts and products, you may think ensuring the lubrication of its rotating components is always checked and maintained. However, because it’s such an obvious check, it’s also easily overlooked or taken for granted. This is especially true for new, qualified operators who may make more assumptions than they should.
Besides checking the lubrication levels, you also want to ensure the lubrication system operates as it’s designed and that the OEM’s recommended maintenance is performed. A well-maintained lubrication system will ensure your spindle’s bearings avoid premature wear and tear and possible failure.
Monitor the Spindle’s Operating Temperature
Like any machinery designed to run a lot and work hard, you don’t want your spindle getting too hot. Yes, that seems obvious, but like lubrication, a spindle’s operating temperature is easy to overlook until it’s too late. That’s why monitoring the spindle’s temperature, especially in a high-demand, high-load work environment is essential to ensuring your spindle remains healthy and doesn’t wear down and fail early in its lifespan.
Check the Spindle Runout
Checking for spindle runout is measuring how much the spindle wobbles around its designated axis of rotation. It should be considered a “failure” regarding operational function if it’s not rotating along this axis. This is because, although the spindle still rotates, it’s not rotating as intended and can lead to defects, poor cuts, and poorly finished surfaces in the final product. Not correcting such an issue can also result in tool breakage, a “failure” no one wants if it can be avoided.
Runout testing can either be done statically or dynamically. Although a static test is easier and will indicate if a major problem occurs, a dynamic test is more accurate if there is a concern where only slight problems with wobbles may be evident.
A non-contact displacement sensor can be used to measure runout in either static or dynamic operation. If a dial tester is available, the test must be conducted by hand in static mode only.
Test the Spindle Vibration
Just as wobbles are a concern for high-speed rotating parts, so is vibration. That doesn’t mean some vibration isn’t expected. However, when vibration affects your spindle’s performance, corrective actions need to be taken. If you don’t, similar problems to unaddressed wobbles result, including bad finishes and equipment failure.
To test and measure spindle vibration, use a vibration sensor (usually an accelerometer or ceramic piezoelectric). The choice of sensor will depend on whether you’re monitoring lateral, transverse, and rotational vibrations and the range you’re concerned about. In addition, your selection will probably be limited to your mounting options. For example, if you want to mount a sensor directly on the spindle, your choice will probably be narrowed down to an accelerometer type.
Whatever sensor you choose, the final data should reveal any defects in the vibration frequency that must be addressed to ensure proper spindle performance.
Inspect the Spindle Motor and Measure Motor Current
If you’re having problems with your spindle’s performance, another thing to check out is the motor and current. The spindle’s prime mover is the motor, providing the tool’s rotational motion. If you’ve got a malfunctioning motor, you’ll probably notice reduced or fluctuating speeds, poor finishes or machined parts that are out of specification, or tool failure.
When inspecting the motor, you’ll also want to measure the motor’s current. If your motor draws too much current, you’ll probably notice damage to the spindle. This is more than likely due to excessive load. To see if this is the issue, use a multimeter to measure the flow of current through the motor. Anything outside normal operating parameters should be corrected before the spindle is further employed.
In addition, monitoring motor current should be a routine maintenance check to ensure optimized spindle performance. Adjusting the feed rate and spindle speed to meet the measured current reduces excessive load and maximizes the tool’s efficiency.
Although there are five tips for monitoring and testing your CNC spindle’s performance listed above, there are more that can easily be added to this list, including:
- Testing Drawbar Force
- Testing Speed
- Analyzing Spindle Sound
- Inspect Individual Components More Closely
The larger point is that precision spindles are essential components of CNC machine tools and, like other components, require constant testing and monitoring with specific attention to detail. You don’t want to be in a position where your equipment’s components, like a spindle, catastrophically fail when they can be avoided through routine maintenance, testing, monitoring, and fixing small problems before they become exponentially larger problems.