Measuring Automobile Wheel Spindle Imperfections and Grinder Wheel Runout

The Cylindrical grinding process is often used for improving wheel spindle surfaces. However, it is important to ensure that this grinding process renders a surface finish that is smooth and defect-free with minimum runout, because any marks or defects left on the surface can result in premature bearing failure and unwanted noise and vibrations.

Challenges Involved in Surface Finishes

Grinder wheel runout

Figure 1. Grinder wheel runout

So far, no grinder has created a perfect surface. Issues such as grinder wheel runout (Figure 1), fixture vibrations, and improperly dressed wheels can cause “chatter” marks on the spindle surface finish. Chatter is a series of repetitive, microscopic waves or imperfections that are present on the surface of the material being machined.

Threshold for Defect Quantification

A major tier 1 supplier to the automotive industry was looking for a way to quantify and classify these imperfections as a 100% quality control check. The customer needed a production environment sensor with high frequency response, small spatial resolution, and large standoff distance to facilitate easy loading and unloading of components.

In addition, the measurement precision had to be below 4 micro-inches with a resolution of 1 micro-inch or better, so as to accurately measure the defects. Moreover, system noise had to be minimal to avoid unnecessary rejection of parts and scraps. The supplier enlisted the help of MTI Instruments to address these issues.

Wheel spindle

Figure 2. Wheel spindle

MTI Instruments worked closely with the customer and produced a special capacitance sensor design to meet the requirements of this project. The probe design included a rectangular sensing element with a measurement range of 0.25mm and an area of 0.020” x 0.10” (0.5 mm x 2.5mm).

Different tip designs were provided using a chamfered or radiussed face to accommodate different configurations of wheel spindle (Figure 2). The probes were utilized in combination with an ultra high-resolution capacitance amplifier, Accumeasure 9000. Also, integrated digital displays instantly alert the operator in real time of the test results.

With this set-up, the system was able to measure, sort, and pass or reject each spindle measured. This initial process ensured improved throughput and also prevented inferior parts from additional machining steps.

This helped in saving a significant amount of cost within the first month of operation. MTI Instruments also solved other application problems such as wheel bolt position and wheel flange runout using similar methods.


MTI Instruments supplies different types of non-contact capacitance sensors. The passive probes are exceptionally thermally stable and can withstand temperatures above 600°C. The company also produces high precision fiber-optic and laser systems with frequency responses up to 500kHz and resolutions to 0.04 micro-inch. MTI has application engineers who provide specific solutions for complex measurement needs.

About MTI Instruments

MTI Instruments is a worldwide leader in the design, manufacture and engineering of non-contact measurement systems and sensors.

MTI’s main products consist of computerized general gauging instruments for position, displacement, thickness and vibration applications based on laser triangulation, fiber-optic and capacitance measurement technologies.

Microtrak Pro 2D Laser Sensor, MTI’s newest product innovation, offers an economical, industrial, high precision solution to your position, displacement and profile applications.

This information has been sourced, reviewed and adapted from materials provided by MTI Instruments Inc.

For more information on this source, please visit MTI Instruments Inc.


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