rotary table

A rotary table is a machining fixture that holds a workpiece and rotates it through precise angular increments. The table sits on the bed of a milling machine or drill press, clamped to the machine's work surface. Its primary job is to let an operator mill, drill, or cut at exact angular positions around a part without moving the cutting tool itself, keeping the cutter at a fixed point while the work rotates beneath it.

The mechanism consists of a circular steel plate mounted on a worm gear drive. A single-turn handwheel with a worm screw meshes with a worm wheel underneath, rotating the table in small, controlled increments. Most tables have either 40 or 90 divisions per full turn, meaning each click of the index lever advances the table by 9 degrees or 4 degrees respectively. Some rotary tables accept a vertical indexing head that bolts to the top, allowing holes to be drilled at angles above the horizontal plane.

Rotary tables come in several standard sizes, typically measured by the diameter of the round work surface. Common sizes are 6 inch, 8 inch, 10 inch, and 12 inch diameter tables. Smaller bench models exist for precision work; large production machines may have power-driven rotary tables with digital readouts that accept CNC input. Direct-drive power tables eliminate handwheel indexing entirely, running off a stepper motor or servo with electronic position feedback.

Setup and common problems

A workpiece clamps directly to the table surface using T-slot work-holding hardware. Centering the part under the cutter is critical: the table's axis must align with the tool's centerline, or cuts will not land at the intended angle. Backlash in the worm gear can cause indexing errors, especially in worn machines; experienced operators compensate by approaching each index stop from the same direction. Overtightening the table lock against the worm gear can strip the teeth.

The rotary table name comes directly from its function, the most straightforward nomenclature in the shop. It is essential for repetitive angular work such as drilling bolt circles, milling keyways equally spaced around a shaft, or cutting a pattern of holes at regular intervals. Without one, the operator would need to either manually measure and position the part for each cut, or set up multiple fixtures. Today rotary tables remain standard equipment in job shops and manual mills, even as CNC machines have reduced their use in high-volume production.