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Improving Machine Tool Performance Using Precision Levels



Did you know that up to 75% of initial errors of a new machine tool can usually be traced to manufacturing, assembly and installation? Machining errors can come from various sources including heat, machine wear, static deflection of machine components, misalignments due to assembly and a soft machine foundation.
We have found good strategies and equipment to significantly reduce errors and keep machine tools running at peak accuracy. From our experience the best place to start troubleshooting is right at the foundation. Our experience shows that incorrect machine tool installation is often the cause of significant and frustrating production errors. The accumulation of small variations within the frame, especially in a multi-axis machine tool, will often result in significant machine motion errors at the tool tip.
For a variety of reasons we like to use high sensitivity electronic levels when we evaluate the geometry of machine tools. The ASME B5.54 standard specifically allows electronic levels for this purpose. What we like about electronic levels is that they show deviation from the horizontal plane measuring the angular relationship such as between a machine guide way surface and the reference of earth’s gravity.  Using an electronic level we check all critical machine components for straightness, pitching, bending or rolling. Level checks are useful for validating all surfaces critical to machine function during the setup of new machines, after rebuilding a machine or as part of an ongoing preventative maintenance program.
We find an advantage using electronic levels over other comparable devices in the resolution of measurement capability. Devices such as Auto-collimators and laser calibration systems can perform many of the same measurements, but the electronic levels can perform these tasks much faster, at less expense and without line-of-site limitations. 
Using an electronic level system, squareness and perpendicularity of a horizontal to a vertical surface such as a machine bed to the column is easy and quick (figure 1). We like to utilize the full travel of the machine tool axes to obtain a more accurate survey. This is often impossible given the length restrictions that are common with other equipment. Using two levels together allows us to quickly and easily make differential measurements.

 

 When using the electronic level system, the angular errors associated with a machine tool can be virtually eliminated when measured by compensating and adjusting for the errors.  Setting up for differential level measurements is easy when measuring pitch and roll along horizontal axes (figure 2), and pitch and yaw in vertical axes. According to ASME B5.54, angular error deviations can also be measured with a laser interferometer or an  autocollimator, but level systems are less expensive, easier to set-up and use, and capable of high accuracy and repeatability.

Taking our process one step further, we always use electronic levels with wireless capability (figure 3) rather than hard wired cables connected to hardware. Bluetooth allows us to do more and do it faster and more accurately. It is our experience that cables create the tendency for the measurements to be influenced by the cables themselves. We also find that cables limit the measurement range and add excess stress due to tangling and snagging. Cables also pick up dirt, grime and oil in a shop environment and restrict our freedom of movement. Finally, using Bluetooth the machine may be operated with its doors closed and the levels inside taking remote measurements via the hand held digital readout.  
We recommend WYLER electronic levels available in the USA from Fowler Precision Tools. From our point of view these are essential tools for any machine tool builder, installer, maintenance engineer or anyone that must insure the performance of the machine tools quality and geometric accuracy.

ABOUT THE AUTHOR:
The author owns a mobile machine tool calibration laboratory Quality Tech Services (QTS), operating for twenty-four plus years throughout the United States and Canada that offers a wide range of On-Site metrology services and equipment.  QTS is ISO 9001:2008 Quality Management System Standard Certified/Registered and AS9100:2009, Rev.C  Aerospace and Department of Defense Standard Certified/Registered. For the scope of On-Site Laser Alignment, Laser Interferometry and Calibration of Machine Tools specifically intended to meet the Aerospace and the Department of Defense  requirements. The Laboratory is also ISO/IEC 17025 & ANSI/NCSL Z540-1 A2LA accredited in the field of calibration. QTS, specializes in Laser Alignment, Laser Interferometry, Machine Tool Calibration, CNC Machine Tool Performance Evaluation, Consultant services and Training.