Thread feed calculator
Calculate the feed for machine tapping: the feed must be exactly spindle speed × thread pitch. The calculator knows the standard thread pitches according to DIN 13-1 from M2 to M16.
Tapping feed
Note: All values are non-binding reference figures. Actual values depend on machine, tool, material and conditions. Start conservatively. No liability is accepted for tool breakage, machine damage or machining results.
What the Thread Feed Calculator Calculates
When machine tapping, the feed rate is not a free variable: for each revolution, the tap must advance by exactly one thread pitch. The calculator therefore multiplies the spindle speed by the pitch of the selected standard thread and gives the matching feed rate in mm/min.
The Formula
vf = n × P
Here, vf is the feed rate in mm/min, n is the spindle speed in rpm, and P is the thread pitch in mm. For example, M6 (pitch 1.0 mm) at 500 rpm: vf = 500 × 1.0 = 500 mm/min.
Pitch and Tap Drill Size According to DIN 13-1
For metric standard threads, the rule of thumb is: tap drill diameter ≈ nominal diameter minus pitch.
| Thread | Pitch P (mm) | Tap drill Ø (mm) |
|---|---|---|
| M2 | 0.40 | 1.6 |
| M2.5 | 0.45 | 2.05 |
| M3 | 0.50 | 2.5 |
| M4 | 0.70 | 3.3 |
| M5 | 0.80 | 4.2 |
| M6 | 1.00 | 5.0 |
| M8 | 1.25 | 6.8 |
| M10 | 1.50 | 8.5 |
| M12 | 1.75 | 10.2 |
| M16 | 2.00 | 14.0 |
What You Should Watch Out For
- Synchronisation: Without a synchronised spindle (rigid tapping), a length-compensating tap holder absorbs small deviations between feed rate and pitch.
- Retraction: At the bottom of the thread, reverse the direction of rotation and retract at the same feed rate.
- Spindle speed: Significantly lower than when milling, in practice often a few hundred rpm (depending on material, tool and machine). Start conservatively.
- Lubrication: Tapping generates high friction. Cutting oil or cutting paste improves surface finish and tool life.
- Alternative thread milling: On CNC milling machines without spindle synchronisation, thread milling is often the more robust solution. Here, the feed rate is not coupled to the pitch.
Frequently Asked Questions
Why must the feed rate be exactly right when tapping?
The tap cuts a helix with a fixed pitch. If the machine feed rate deviates from this, the tool pushes or pulls against the already cut thread flanks. The thread is damaged or the tap breaks. Therefore: feed rate = spindle speed × pitch.
What is the difference between rigid tapping and a length-compensating tap holder?
With rigid tapping, spindle rotation and Z-axis feed are rigidly synchronised by the controller, including during direction reversal. A length-compensating tap holder, on the other hand, holds the tap with spring action in the axial direction and compensates for small deviations mechanically. It is the usual solution when the machine does not have a synchronised spindle.
What tap drill size do I need for a metric thread?
As a rule of thumb for standard threads: tap drill diameter equals nominal diameter minus pitch. For M6 with a pitch of 1.0 mm, this is 5.0 mm. The table above lists the common values from M2 to M16.
Can I cut threads on a CNC gantry milling machine?
Yes. With a synchronised spindle using a rigid tapping cycle, otherwise with a length-compensating tap holder. An alternative is thread milling: a thread mill creates the profile on a helical path without the feed rate being coupled to the pitch.
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