Choose a threading method
Compare cutting taps, forming taps, thread milling, lathe threading, dies and rolling for your material, hole type and production volume.
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Decision parameters
Catalog reference: 120-150 HB · Elongation: ≥26%.
Equipment and conditions
Result Recommended threading methods
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⚠ Indicative shop recommendation: it does not replace the judgement of a qualified professional. Always check the threading method, the tool, the parameters and the result on the part before machining or running production.
What you should take into account
- ·Material, condition and machinability (alloy, temper, hardness and elastic recovery).
- ·Thread standard and profile (metric, UNC, pipe, trapezoidal…), pitch, hand and required tolerance.
- ·Interior or exterior, through or blind hole, useful depth and accessibility to evacuate chips.
- ·Available machine (lathe, machining center, manual), clamping rigidity and fixture changeover.
- ·Production volume, part value and risk of leaving a broken tool inside the hole.
- ·Pilot hole, lubrication/coolant and manufacturer tables for tap, mill or insert.
- ·Surface finish, concentricity and dimensional control with Go/No-Go gauge or per drawing criterion.
- ·Drawing, customer specification and sealing requirements (pipe, gasket, sealant).
Comparison of methods
Guidance criteria by technique. ✓ favorable · ~ acceptable · ✗ unfavorable.
| Method | Coste | Velocidad | Seguridad | Acabado | Agujero | Material | Producción |
|---|
Workshop tips and common problems
Technique selection and troubleshooting for the method Tap. Use the method chips above to change techniques.
How to do it right
Tap: spiral flute, spiral point or straight flute
A spiral point (gun tap) pushes chips forward in through holes; a spiral flute evacuates upward in blind holes; straight flutes suit short-chipping materials such as cast iron or brass. Choose the helix angle according to the material's toughness.
Rigid vs. Rigid Threading floating
Rigid tapping (G84/CYCLE84) synchronizes spindle and feed: essential on modern CNC and blind holes. The floating tap holder compensates small sync errors on older machines, but gives less depth control.
Speed and lubrication by material
Carbon steel: 8–15 m/min with cutting oil. Stainless: lower to 4–8 m/min and lubricate abundantly to avoid harshness. Aluminum: 15–30 m/min with polished or TiN core to prevent clogging. Casting: dry or with air.
Useful depth in blind hole
Leave 2–3 pitches of run-out beyond the usable thread: the tap needs room for its lead chamfer and the accumulated chips. Program the hole bottom deeper than the thread so you don't jam the tap.
Go/No-Go gauge inspection
For production valid with Go/No-Go gauge, flank micrometer (3 wires) or plane criterion. The correct drill does NOT guarantee an accepted thread - the tolerance is checked on the flank, not the diameter of the drill bit.
If something goes wrong · symptom → cause → solution
⚠ Tap broken inside the hole
Causes: undersized pilot hole, insufficient lubrication, chips not cleared in a blind hole, misalignment or unsynchronized feed. Fix: open the drill toward the recommended thread %, improve coolant, use rigid tapping and clear chips in deep cycles (peck).
⚠ No-Go Gauge enters (oversized thread)
Causes: worn or oversized tap, excessive float runout, elastic recovery of the material or a tap wrong for the material. Fix: change the tap, reduce tap-holder clearance, lower the speed on springy materials and check the tap class.
⚠ Gauge Go does not fit (tight thread)
Causes: insufficient cutter compensation, insert not reaching depth, burr on the crest or a pilot hole too large with a forming tap. Fix: adjust compensation/depth, deburr the entry and check the forming drill isn't oversized.
⚠ Entrada acampanada (bell-mouth)
The thread ends up wider at the mouth than at the bottom. Causes: tap not perpendicular, unguided start, spindle play or too much float. Fix: start with a guide or feed synchronized from the first thread, check perpendicularity and reduce tool-holder play.
⚠ Poor finish or torn flanks
Causes: high cutting speed in soft/gummy material, worn edge, poor lubrication or a last pass with too much infeed. Fix: lower Vc on aluminum/stainless, change the edge, improve coolant and add a spring pass with almost no depth.
⚠ Incomplete thread at the bottom (blind)
Causes: usable thread programmed to the bottom of the hole with no reserve, or a straight-flute tap that doesn't reach. Fix: drill deeper leaving 2–3 pitches of run-out, use a bottoming tap only for the last threads and check the real usable length.
Other threading tools
Technical Guide: How to Choose the Right Threading Method
Reference article for this section. Switch goal above (drill, identify, CNC, method, repair or base plate) to see the guide for that tool.
Taps, thread mills, lathe inserts, dies and thread rolls all solve the same problem — producing a thread — with different trade-offs in cost, speed, breakage risk and finish. The right choice depends on the material, the type of hole, the production volume and the required tolerance.
Compare material, blind or through hole and production volume. Available machines and tools also determine which process is suitable.
Cutting tap vs. form tap vs. thread mill
El macho de corte es el método más universal y económico, válido para casi cualquier material y volumen. La laminación (forming) no genera viruta y da roscas más resistentes a fatiga, pero exige material dúctil y un taladro previo mayor. La fresa de roscar por interpolación helicoidal es la opción más segura en diámetros grandes, materiales duros o agujeros ciegos críticos, porque un macho roto dentro de la pieza es mucho más caro de resolver que ajustar un programa de fresado.
As a rule of thumb: use forming for high-volume fasteners in ductile material, a cutting tap for other standard production runs, and a thread mill when the risk of breaking the tool inside an expensive part is unacceptable.
Insert lathe threading: when does it make sense
If the part is already in the lathe and the thread is an external or internal thread of revolution, single-point threading avoids a machine change. G76 is preferable in production because it distributes the passes automatically; G32/G92 give more manual control pass by pass, useful for repair or prototypes.
With coarse pitches or small diameters, the thread's helix angle may require a shim plate so the insert does not rub on one flank: check the shim plate calculator if you see uneven wear or a poor finish on one flank.
Threading and rollers: manual and high production methods
The die is the manual option par excellence for maintenance, prototypes or repairing external threads without CNC: it is not the most repeatable method for tight tolerances, but it needs no machine investment. Thread rolls are the opposite extreme: high upfront investment, but minimal cost per part on very long fastener runs, always in ductile materials.
Pipe threads, plastic and repair insert: special cases
Pipe threads (BSP/NPT) combine mechanical fastening and sealing, so the method is chosen by whether you need to seal with a gasket (parallel) or by the taper (tapered), not just by the material. In plastic or 3D printing, consider a heat-set insert on parts that will be dismantled several times, rather than tapping the base material directly.
If the original thread is already damaged, repair with an insert (coil or solid socket) almost always beats trying to remake the nominal thread in the same hole.
Frequently asked questions: How to Choose the Right Threading Method
When is it convenient to mill a thread instead of using a tap?
Thread milling is worthwhile on large threads, hard materials, critical blind holes or high-value parts where you cannot risk leaving a broken tap inside. A thread mill also covers several diameters of the same pitch with one tool.
What is the difference between cutting core and rolling core?
The cutting tap removes chips and is more universal; The rolling method deforms the material without cutting it, gives threads that are more resistant to fatigue, but requires ductile material, good lubrication and a larger pre-drill.
Does roller lamination work on cast iron or very hard steel?
Not advisable: forming requires the material to flow without cracking, and cast iron and very hard steels are too brittle or too resistant to deformation for that. In those materials, use a cutting tap or a thread mill.
What threading method is best for high production of fasteners?
Rolling rollers are the most profitable in very long series of ductile material: they do not generate chips, give a good surface finish and improve the fatigue resistance of the fillet against cutting.
When do I need a shim in lathe threading?
When the thread's helix angle (due to a coarse pitch, a small diameter or multiple starts) departs from the usual 1° of a standard holder, or when the thread hand does not match the tool hand. Use the shim plate calculator to get the angle and the indicative AE/AI code.
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