CNC threading and tapping put the threads on shafts, studs, fittings, and housings that hold the machined world together. The method you pick, single-point threading, thread rolling, cut tapping, or thread milling, drives the part's strength, finish, and cost. This guide breaks down each threading process, explains thread classes and gauging, and gives realistic cost ranges so engineers and buyers can spec threads correctly the first time.
Threading Methods on a CNC Machine
There are two ways to form a thread: cut it, which removes material, or roll it, which displaces material. Each cutting method suits different geometry and volume.
Single-Point Threading
Single-point threading uses one carbide insert that traces the thread profile over multiple passes on a CNC lathe. It is the most flexible method because one insert can cut a wide range of pitches and diameters.
- Best for medium-volume turned parts, large diameters, and non-standard pitches
- Handles internal and external threads, tapers, and multi-start threads
- Typical class of fit: 2A/2B standard, 3A/3B with controlled passes and gauging
- Surface finish of Ra 32 to 63 uin on the flanks
Thread Rolling (Rolled Threads)
Thread rolling presses hardened dies against the blank to cold-form the thread. No material is removed, so the grain flows around the thread form.
- Produces the strongest threads because the cold-worked grain resists fatigue and stripping
- Fast and ideal for high-volume fasteners and studs
- Excellent surface finish, often Ra 8 to 16 uin on the flanks
- Limited to ductile materials and external threads on cylindrical blanks
Cut Threads (Tapping and Die Cutting)
Cut tapping drives a tap through a drilled hole to form internal threads, the workhorse for tapped holes. Cut threading with a die produces external threads. Cutting is versatile and works on hardened and brittle materials that cannot be rolled.
- Standard for internal threads in housings, plates, and bosses
- Works on nearly any machinable material
- Thread strength is lower than rolled because the grain is severed
- Rigid tapping on our machining centers controls depth and lead precisely
Thread Milling
Thread milling uses a rotating multi-tooth cutter interpolated in a helix. It is the safest method for large, deep, or high-value parts because a broken thread mill is easy to retract, unlike a snapped tap. It also cuts both left and right hand threads with one tool.
Understanding Thread Classes
A thread class defines the tolerance and allowance of the fit. For Unified inch threads the letter A means external and B means internal, and the number sets the tightness.
| Class | Fit | Typical Use |
|---|---|---|
| 1A / 1B | Loose | Fast assembly, dirty environments, quick spin-on |
| 2A / 2B | Standard | General commercial fasteners and most machined parts |
| 3A / 3B | Tight | Aerospace, defense, and precision assemblies with no slop |
Metric threads use a similar system, for example 6g external and 6H internal for a general-purpose fit. We verify threads with go/no-go ring and plug gauges and document pitch diameter on our Brown & Sharpe CMM during first article inspection. Class 3A/3B and defense work ship with material certifications and full FAI reports.
Common Thread Standards We Machine
- UNC and UNF unified coarse and fine, such as 1/4-20 and 1/4-28
- Metric coarse and fine, such as M6x1.0 and M6x0.75
- NPT and NPTF tapered pipe threads for sealing fittings
- ACME and stub ACME for lead screws and power transmission
- Custom and multi-start threads by single-point or thread milling
How to Choose the Right Threading Method
- Need maximum strength or fatigue life? Roll the thread. Rolled threads outlast cut threads under cyclic load.
- High volume external threads on ductile material? Thread rolling gives the lowest cost per part.
- Large diameter, non-standard pitch, or tapers? Single-point threading is the flexible choice.
- Internal threads? Rigid tapping for standard sizes, thread milling for large, deep, or high-value bores.
- Hardened or brittle material? Cut or mill the thread, since rolling needs ductility.
CNC Threading and Tapping Cost Guidance
Threading cost depends on method, class, and gauging. The ranges below are typical illustrative estimates for adding threads to a machined part, not binding quotes. Get a firm price with an instant quote.
| Cost Driver | Typical Range | Notes |
|---|---|---|
| Programming and setup | $120 to $500 per job | Higher for multi-start or custom pitches |
| Tapping (per hole) | $0.15 to $1.25 | Rigid tapping; deeper and larger holes cost more |
| Single-point threading | $0.75 to $4.00 per feature | Multiple passes add cycle time |
| Thread rolling | $0.05 to $0.50 per part | Lowest cost at high volume |
| Gauging and CMM (class 3A/3B) | $60 to $250 per lot | Go/no-go plus CMM pitch diameter verification |
Tips to Control Threading Cost
- Specify 2A/2B unless the assembly truly needs 3A/3B, since tighter classes add passes and gauging.
- Standardize on common pitches like UNC/UNF to use stock tooling.
- For high-volume studs, design for thread rolling to cut both cost and cycle time.
- Call out thread length and depth clearly to avoid over-threading and broken taps.
Wexmar Threading and Tapping Capability
Wexmar is a precision CNC machine shop in Canastota, NY. We single-point thread and rigid-tap on 10 Mazak and Doosan CNC turning centers, thread-mill on 6 Mazak horizontal machining centers, and roll and whirl threads on our Maier Swiss machines. We are SAM.gov and CAGE registered, machine DFARS-compliant material, and every thread is gauged and, when required, verified on our Brown & Sharpe CMM. All work is made in the USA and shipped nationwide with ISO 9001-aligned documentation.