The spindle core diameter is the smallest diameter measured between the deepest points on opposite sides of the thread. It essentially describes the diameter of an imaginary cylinder that runs precisely through the thread roots, thereby indicating the thread’s smallest cross-sectional area.
A larger core diameter increases the load capacity and resistance of the thread drive against breakage, which is particularly effective in applications exposed to high mechanical stresses. A smaller diameter, however, allows for finer and more precise movements, which is advantageous in applications such as measuring instruments or precision mechanical systems.
The core diameter can be determined by various methods, depending on the type of thread (metric, trapezoidal, etc.). For metric threads, the core diameter is often specified directly, while for trapezoidal threads, additional calculations may be required.
Practical Examples
For a metric thread (M10), the core diameter is approximately 8.5 mm, meaning the spindle has this diameter at the thread root. For a trapezoidal thread (Tr20 × 4), the core diameter is approximately 16 mm, which is crucial for the load capacity and application of the thread drive.
