KEVOS® MAKEOS · Threads
Tapping Plan (Tap Drill, Thread Percentage, Speed and Cycle Time)
What tap drill gives the thread percentage I want, what percentage will the drill I have give, and how long does a batch of tapped holes take?
Plan of a tapping operation for a metric thread: the tap drill for a target thread percentage for cut or formed taps and the basic minor diameter (as the tap drill tool), the percentage the drill you actually have gives, spindle speed from tapping speed held to the machine maximum, synchronous feed and forward time (as the tapping feed tool), reverse time at the retract speed multiple, and the batch time.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Thread diameter | mm | Nominal diameter of the thread. |
| Pitch | mm | Thread pitch. |
| Thread percentage wanted | % | Thread engagement wanted (about 65–75% for cut taps; higher for forming taps). |
| Tap type | choice | Cutting or forming tap (forming taps need a larger hole). |
| Drill you have (0 = use the calculated size) | mm | Drill size available; 0 uses the calculated size. |
| Smallest thread percentage accepted | % | Lowest thread percentage you accept (strength). |
| Largest thread percentage accepted | % | Highest thread percentage you accept (tap breakage, torque). |
| Tapping speed | m/min | Tapping speed for the tap and material. |
| Largest tapping spindle speed | rpm | Highest spindle speed for tapping on the machine. |
| Thread depth | mm | Depth of full thread. |
| Retract speed ÷ forward speed | Retract speed as a multiple of the forward speed. | |
| Positioning and dwell per hole | s | Rapid positioning and dwell per hole. |
| Holes in the batch | Number of holes to tap. |
Method and formulas
- Tap drill = D − k × percentage × P, with k = 0.01299 (cut) or 0.0068 (form) per percent; basic minor diameter = D − 1.0825P (as the tap drill tool).
- Percentage given by a drill = (D − drill) ÷ (k P).
- n = min(1000 v_c ÷ π D, n_max); feed = P × n; forward time = depth ÷ feed (as the tapping feed tool); retract time = forward time ÷ retract multiple.
- Example: 8.5386 mm gives 75%; a 8.5 mm drill gives 76.982%. At 318.31 rpm a batch of 100 takes 8.0457 min.
Limitations
- Basic 60° metric thread; hole size in tough or soft materials may need adjusting.
- Thread percentage relates to engagement, not directly to strength; 75% gives most of the full strength.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose a tap drill for strength or tap life
- Check a standard drill’s thread percentage
- Estimate tapping time for a batch
Who it is for
- CNC machinists
- Process planners
- CNC programmers
What you get
- Tap drill for the target and the drill’s actual percentage
- Spindle speed and synchronous feed
- Time per hole and per batch
Interpreting the result
- Raising thread percentage above about 75% adds little strength but much more tapping torque.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2029–2036. Topic reference; no source tables or recommended settings are reproduced.
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Open the Tapping Plan (Tap Drill, Thread Percentage, Speed and Cycle Time) calculator
