Tolerance Analysis and Re-distribution of A Machine Tool Spindle by Negative Tolerancing

Machine tool spindle is among the most precise components which require both high accuracy and high repeatability. It has been an issue how to distribute components’ tolerances in order to reduce production cost while keep the tolerance target under control. This paper investigates the method for tolerance re-distribution of a spindle in order to keep its high assembly tolerance. The dimensional chain of the spindle is first constructed to analyze the assembly tolerance. While the assembly tolerance is out of the target, the reverse process that re-distributes the target tolerance to each component is investigated such that the target can be satisfied and controlled. Tightening tolerances of spindle parts is the most straightforward approach to reduce the assembly tolerance that, however, increases manufacturing cost. An approach to re-distribute the components’ tolerance based on the IT precision grade is then assigned and analyzed. This approach, however, still fails to achieve the required tolerance target. The “negative tolerancing” approach is then employed. The retaining ring of the spindle severs as the adjusting component which carries “negative tolerance” to compensate the assembly tolerance. The result shows that the tolerance target can be achieved using this approach without paying high manufacturing cost.