Tap Drill Size for Thread M3.5 x 0.6

Thread data M3.5 x 0.6: major diameter, pitch and recommended tap drill before tapping.

Rosca seleccionada

M3.5 x 0.6Ver datos completos

Coarse ISO Metric · Calculado por fórmula básica

Dimensiones de referencia

Paso
0.6 mm
Ø mayor
3.5 mm
Ø medio aprox.
3.11 mm
Ø menor aprox.
2.85 mm

Perfil y norma

Perfil
60° ISO
Norma / familia
ISO Metric
Forma
Perfil triangular ISO
Angle
60°
Tipo
Paralela

Fillet geometry

Theoretical height H
0.52 mm
Profundidad radial
0.368 mm
root radius r
0.087 mm

Tolerancias

Tornillo (ext.)
6g
Tuerca (int.)
6H
Norma de tolerancia
ISO 965-1
Desv. fund. pos. g
-21 µm
Desv. fund. pos. h
0 µm

Clase 6g/6H cubre ~80% de aplicaciones generales. Límites exactos en ISO 965 u otra norma aplicable.

Medida por 3 hilos

Para verificar Ø medio en roscas exteriores con micrómetro y pasadores calibrados.

Ø hilo óptimo
0.346 mm
M sobre hilos
3.24 mm

CNC programming

F por vuelta
F0.6
Synchronized advance
360 mm/min
Taladro previo orientativo
Ø2.9 mm

Notas

  • Geometría base calculada por fórmula ISO métrica.

Factores que definen el taladro previo

Result · Recommended pre-drill

Generate CNC cycle

Taladro previo recomendado

Ø2.9 mm

Teórico: Ø2.9 mm · 75% rosca efectiva

Min. drill depth

≈ 12.6 mm

Rosca 12 mm (3.429D) · riesgo muy profunda

⚠ Cálculo orientativo de taladro previo: no sustituye el criterio de un profesional cualificado. Verifica siempre diámetro de broca, profundidad, método de roscado y resultado en pieza con plano, galga y catálogo del fabricante antes de mecanizar.

How to interpret the pre-drill

  • M3.5 x 0.6 (3.5 mm, paso 0.6 mm, Métrica ISO gruesa) en low-carbon steel s235 / st37, agujero through, método macho de corte.
  • Broca objetivo Ø2.9 mm para 75% de rosca efectiva (objetivo «equilibrado 70-75%»; rango sugerido 70-75% en low-carbon steel s235 / st37).
  • Geométrico antes de broca comercial: Ø2.9 mm. La broca de stock más cercana puede diferir ligeramente; valida con galga Go/No-Go si la pieza es crítica.
  • Con laminación al mismo 75% el piloto subiría a Ø3.2 mm (teórico Ø3.2 mm) porque el material se desplaza en lugar de evacuarse.
  • Macho Punta helicoidal (pasante): en pasante la evacuación es más sencilla; el diámetro sigue gobernado por el 75% de rosca efectiva.
  • Profundidad útil roscada 12 mm → taladra al menos ≈12.6 mm (≈3.429D, riesgo muy profunda).
  • 75% de rosca efectiva está en el rango habitual (70-75%); ajústalo si el par es excesivo o la galga No-Go entra demasiado fácil.

Process recommendation

  • Taladra Ø2.9 mm y rosca a 75% efectiva con punta helicoidal (pasante) en low-carbon steel s235 / st37.
  • Low-carbon steel S235 / St37: si M3.5 x 0.6 trabaja con carga, confirma Ø2.9 mm con galga Go/No-Go.
  • Agujero pasante: Ø2.9 mm es suficiente en diámetro; la viruta sale por el fondo con punta helicoidal (pasante).
  • Rigidez normal: conserva margen en M3.5 x 0.6, sobre todo en agujeros ciegos y roscas ≤M6.
  • Taladrina estándar en low-carbon steel s235 / st37: afecta par y vida útil del macho, no el diámetro teórico Ø2.9 mm.
  • Rosca 3.429D (12 mm útiles): el par acumulado pesa más que afinar 75%; revisa evacuación y profundidad ≥12.6 mm.

Rosca muy profunda: evita porcentajes altos de rosca efectiva, usa macho/fresa específica para agujeros profundos y controla evacuación.

Quick guides and troubleshooting

Technique selection and troubleshooting for the method Tap. Change the threading method above for specific tips.

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.

Technical guide: how to calculate the pre-drill before threading

Reference article for this section. Switch goal above (drill, identify, CNC, method, repair or base plate) to see the guide for that tool.

The tap drill is the variable that causes the most broken taps and out-of-tolerance threads on the shop floor. There is no single fixed formula: it depends on the method (cutting or forming), the percentage of thread engagement, the material and whether the hole is blind or through.

Why is "major diameter minus pitch" not the whole story?

The quick rule of subtracting the pitch from the nominal diameter (for example M8 x 1.25 → 8 − 1.25 = 6.75 mm) gives a drill for roughly 75% thread engagement, the usual value in medium-machinability steel. That figure changes if you need more thread strength (raise the % and lower the diameter) or less tapping torque (lower the % and raise the diameter).

Our calculator starts from the ISO 68-1 geometric formula (60° triangular profile) and adjusts the result to the % of effective thread you choose, before rounding up to the nearest commercial drill bit.

Cutting male vs. rolling tap: the drill changes a lot

A cutting tap removes chips, so the tap drill is smaller (more material to remove). A forming tap does not cut: it pushes and displaces the material to form the thread, so it needs a noticeably larger drill and a ductile material (elongation >5%) to avoid cracking the crest.

If you roll in a material that does not flow well (cast iron, very hard steels), the thread may come out incomplete or cracked no matter how much you adjust the drill: in those cases, use a tap or thread mill instead.

Pipe threads (NPT, BSP): why they are not calculated the same

NPT, BSPT y NPTF son roscas cónicas (conicidad aproximada 1:16): el diámetro cambia a lo largo de la rosca, así que el ajuste no se define por un taladro con fórmula directa sino por el número de vueltas de apriete hasta el plano de galga. BSP y NPS, en cambio, son paralelas y sí admiten una aproximación por fórmula triangular parecida a la métrica, aunque siempre conviene validar con galga de tolerancia A/B.

Never apply the metric "major minus pitch" rule to an NPT or BSPT: the drill and depth of these pipe threads come from the manufacturer's table and the gauge, not from a standalone calculation.

Blind hole vs. intern: the margin that is forgotten

In a blind hole you must drill deeper than the usable thread length, to leave room for the tap's lead chamfer and for chips that cannot escape forwards. In a through hole the chips exit the other side and the margin needed is minimal.

A helical tip tap (gun tap) pushes the chip forward and is the best option for high-speed through-hole; In the blind, a helical channel male that evacuates upwards reduces the risk of jamming and breakage.

Frequently asked questions: how to calculate the pre-drill before threading

How do you calculate the exact diameter of the threading bit?

For metric threads the base ISO formula is major diameter minus pitch, adjusted for the % of thread engagement. For example, M8 x 1.25 at 75% engagement gives a theoretical drill of 6.75 mm, rounded to the commercial 6.8 mm drill. In production, always validate with a Go/No-Go gauge.

Does the drill switch between cutting tap and rolling tap?

Yes, quite a lot: a forming tap needs a larger drill because it displaces the material instead of removing it. Using a cutting-tap drill with a forming tap usually stops the tap from forming the full thread.

Can I calculate the bore of an NPT or BSP thread the same as a metric one?

Not for tapered threads (NPT, BSPT, NPTF): they depend on the gauge plane and the number of turns of engagement, not on a fixed diameter formula. BSP and NPS, being parallel, do allow a formula-based approximation, but you must always confirm with a pipe gauge and the manufacturer's table.

How much more do you have to drill in a blind hole?

As a guide, add between 2 and 4 thread pitches beyond the usable length for the tap's chamfer and chip evacuation, adjusting for the tap geometry (spiral point, spiral flute or straight flute).

What happens if I increase the effective thread percentage?

More % of effective thread gives more thread strength, but also more threading torque and more risk of breakage of the tap, especially in small taps (M3-M6) or demanding materials such as stainless or hardened steel.

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