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A 100mm semi-universal dividing head is also known as an indexing head or a spiral head. It is an essential tool you use in the field of metalworking, especially for precise milling and other machining operations. You use it to hold a workpiece in a specific position and rotate it to precise angles. This allows the machining of various geometric features. Below, I’ll discuss the key features, uses, and other considerations of a 100mm semi-universal dividing head.

Key Features

  1. Size: The “100mm” in the name refers to the size of the chuck or the faceplate diameter, which is roughly 4 inches. This size is suitable for handling small to medium-sized workpieces.
  2. Construction: Typically constructed from high-grade cast iron or steel, dividing heads are robust and designed for precision. The semi-universal type allows for some degree of tilt in addition to rotation, providing flexibility for angular setups.
  3. Indexing Mechanism: This allows the operator to rotate the workpiece to precise increments. The dividing plate with holes drilled at specific intervals interacts with an indexing pin or crank, facilitating exact rotations.
  4. Chuck: It features a chuck or you can fit it with a collet system for holding the workpiece. The chuck allows for quick adjustments and securing of the workpiece.
  5. Gear Ratios: The gear train in a dividing head is adjustable for different ratios, enabling various division operations without needing to swap out the dividing plate.

Common Applications

  • Machining Gear Teeth: One of the most common uses of dividing heads is in the cutting of gears. By setting the gear ratio and using a suitable cutter, you can machine the teeth of a gear precisely.
  • Drilling Patterned Holes: For projects requiring precise and patterned hole drilling in circular arrays, like in a flange or a hub, a dividing head is indispensable.
  • Complex Machining: It allows for machining at various angles and planes, enabling complex shapes and surfaces like spirals.


  • Dividing Plates: These are critical for achieving the necessary divisions. They come with different configurations of holes for various dividing options.
  • Tailstock: Similar to that used on a lathe, a tailstock supports the other end of the workpiece, especially useful for longer items.
  • Drive Gear: You might need additional gears for specific machining tasks that require unique gear ratios.

Usage Tips

  • Accuracy Check: Regularly verify the accuracy and alignment of the dividing head to ensure precision in machining tasks.
  • Lubrication: Maintain proper lubrication of the moving parts to prevent wear and to keep operation smooth.
  • Secure Mounting: Always ensure the dividing head is securely mounted to the machine table and that the workpiece is tightly clamped to avoid any movement during machining.
  • A 100mm semi-universal dividing head is a highly beneficial addition to a milling setup, particularly when precision and versatility in machining operations are required. It enhances the capability to produce intricate and precise parts in a workshop setting.