G84 is the canned cycle for tapping threads: it feeds to depth in time with the spindle, reverses the spindle, and feeds back out. The feed rate must equal the thread lead times the spindle speed so the tap tracks the thread.
Format
How it works
- The spindle and Z feed stay synchronized through the cycle, then the spindle reverses to back the tap out.
- Feed must match the thread pitch; a rigid tapping head or tension-compression holder absorbs small errors.
- G80 cancels the cycle.
Example
G84 Z-0.5 R0.2 F25.0 (1/4-20 at 500 rpm: 500 / 20 = 25 ipm)
FAQ
Can I use G84 with any tap? G84 assumes a rigid tapping setup where the spindle and Z-axis are synchronized so the tap advances exactly one pitch per revolution. Without rigid tapping capability, a tension/compression tapping head is typically required instead.
What happens if the spindle isn’t ready for rigid tapping? Without rigid tapping enabled or supported, G84 either faults or behaves unpredictably, since the cycle depends on precise spindle-to-Z synchronization that a standard, non-rigid spindle setup can’t provide.
Related: Tap Drill Chart and Thread Dimensions Chart.