thrill
To drill and thread in one operation, using a tool bit that cuts the hole and the threads in one series of computer-controlled movements.
thrill: drilling and threading done as one move
To thrill is to cut both a hole and its internal threads in a single operation, using a specialized tool bit on a CNC machine. The bit advances into the workpiece, cuts the hole to size, and then cuts the thread profile all in one continuous feed, eliminating the need for a separate threading step. This saves cycle time and reduces tool changes on the machine tool.
The thrill bit itself is a complex cutting tool, typically made from high-speed steel or carbide, with multiple cutting edges ground to perform both drilling and thread-cutting functions. The bit must be rigid enough to handle the combined loads of drilling and threading without deflection, which can cause oversized holes or mis-pitched threads. Coolant delivery is critical, as the tool must maintain temperature while managing the chips generated by both operations.
When thrilling works and when it doesn't
Thrilling is most effective in production runs where the same threaded hole appears many times, or where hole and thread depth are modest, typically up to about 2.5 times the hole diameter. Materials that machine cleanly, such as aluminum alloys and brass, are ideal. Cast iron, stainless steel, and tough materials can cause tool breakage or poor thread quality because the combined cutting forces spike during the threading phase. Hole position tolerance and spindle runout become critical, since any eccentricity translates directly into an out-of-tolerance thread.
The term thrill is a portmanteau of thread and drill, though it is sometimes called thread-drilling or combination threading in technical documentation. CNC control is essential, because the tool must transition smoothly from drilling speeds and feeds to threading speeds and feeds without stopping, and the machine must hold tight tolerances on depth and rotation speed. Manual or conventional machines cannot perform this operation reliably.
In high-volume injection molding, automotive, and aerospace production, thrilling has become standard for mounting holes, sensor bosses, and other common fastener holes. The time savings per part are small, often only a few seconds, but they compound across tens of thousands of parts. The trade-off is tool cost and the need for CNC capability, which makes thrilling uneconomical for one-off or low-volume work where separate drilling and tapping remain the norm.