📦 P-GROUP · MOST COMMON DEEP HOLE MATERIALS

Carbon & Alloy Steel

Carbon and alloy steels are the most common materials for deep hole drilling. Lower carbon = better machinability. Higher alloy content requires reduced Vc and tougher tool grades. AlTiN+ coatings permit 10–15% higher cutting speeds.

5GradesLow C to hardened alloy

40–180m/min VcBy carbon/alloy content

50–100barCoolant pressure

Ra 0.1–1.6μmAchievable finish

PROPERTIES

Material Properties & Speeds

Material	HB	Characteristics	Vc (m/min)
Low-carbon (<0.25%C)	~125	Good machinability, continuous chips	120–180
Medium-carbon (0.25–0.45%C)	~180	Balanced properties	100–150
High-carbon (>0.45%C)	~220	Higher hardness, control Vc	80–120
Low-alloy steel (annealed)	~200	High toughness, chip breaking critical	60–80
Alloy steel (quenched & tempered)	~300	High hardness, reduce Vc	40–60

FEED RATES

Feed by Diameter

Drill Dia (mm)	Carbon Steel (mm/rev)	Alloy Steel (mm/rev)
3–5	0.006–0.037	0.005–0.030
6–10	0.010–0.109	0.008–0.090
10–12	0.025–0.174	0.020–0.140
16–20	0.050–0.209	0.040–0.170
20–24	0.060–0.254	0.050–0.200
32–40	0.096–0.455	0.080–0.360

Start from the lower bound; increase based on chip shape and surface finish.

SPECIFICATIONS

Key Data

50–100

bar

Coolant pressure

TiAlN

Coating

AlTiN+ for +10–15% speed

Oil

Coolant type

Oil-based recommended

0.1–1.6

μm Ra

Achievable surface finish

C-shape

Chips

Tight curled = good breaking

Pilot

Hole

80–90% dia for >250 HB

RECOMMENDATIONS

Parameters & Best Practice

💡 Tooling: Standard carbide gundrill or BTA head. TiAlN coating for general use. AlTiN+ coating permits 10–15% higher cutting speeds. For alloy steels, use tougher substrate grades.

💡 Coolant: Oil-based, 50–100 bar (higher end for L/D >20:1). Low-carbon steel: 50–70 bar typically sufficient. For alloy steels, maintain 70–100 bar for optimal chip breaking (Vellfire Tools, 2026).

💡 Chip breaking: Medium-carbon and above requires an effective chip breaker. Tight curled chips = good. Long ribbons = insufficient feed or worn chip breaker. For alloy steels over 250 HB, use a pilot hole at 80–90% of full diameter to reduce axial forces.

⚠️ Hardness fluctuations: In quenched & tempered steels, unstable cutting forces can occur. Verify material uniformity before machining. When transitioning between case-hardened and core material, reduce feed 20–30% through the transition zone.

SURFACE FINISH

Achievable Ra (Published Data)

Material	Condition	Ra (μm)	Source
Low-alloy steel (UTS <1200 MPa)	Deep-drilled, optimized	0.11 ± 0.11	Michler et al., 2024
Pipeline steel	Deep-drilled hollow specimen	0.14 ± 0.02	Michler et al., 2024
Carbon steel (general)	Standard deep hole drilling	0.4–1.6	Industry data
AISI 1045 (dry helical milling)	Optimal Vc 35 m/min, f 0.15	~3.8	JETS, 2025

💡 Note: Deep hole drilling achieves significantly better Ra than conventional drilling due to the burnishing action of guide pads. Quenched & tempered steels can produce mirror-like finishes (Ra <0.2 μm) under stable conditions.

PROS & CONS

Strengths & Limitations

✅ Advantages

Widest familiarity — parameter data is abundant and reliable
Predictable chip formation & evacuation on most grades
Excellent surface finish (Ra 0.1–1.6 μm) via pad burnishing
Broad tooling and coating choice, including indexable options

⚠ Limitations

Long, stringy chips on low-carbon grades need effective chip breakers
Alloy / quenched-tempered grades force low Vc and tougher substrates
Hardness fluctuations cause unstable cutting forces and drill wander
Case-hardened transitions require reduced feed through the zone

PROCEDURE

Setup & Start-of-Cut

Confirm material condition

Verify grade, hardness, and bar straightness — a bowed bar guarantees bore drift.

Pilot / guide

For >250 HB or L/D >12:1, pre-drill a pilot at 80–90% diameter, or set the entry bushing.

Coolant on

Full pressure before engagement; oil-based 50–100 bar (70–100 bar for alloys).

Engage & ramp

Start at reduced feed for the first 2–3×D, then ramp to target feed.

Verify chip form

Tight C-chips confirm the feed/breaker is right; adjust feed before speed if ribbons appear.

Monitor & finish

Track coolant pressure and spindle load; retract with coolant flowing, stop coolant after tool clears.

APPLICATIONS

Where Carbon & Alloy Steel Deep Holes Are Drilled

🔨 Hydraulic CylindersBarrel bores in 4140 / ST52 tube stock, L/D up to 40:1, finished by skive & burnish

🔗 Crankshafts & CamshaftsOil passages in medium-carbon forgings, gundrilled at high volume

🔧 Die & MoldCooling channels in P20 / tool steel plates

🏭 Machinery ShaftsAxial bores in transmission and motor shafts

📝 Oil & GasDrill collar and valve components in alloy steels

🚘 AutomotiveFuel rails, gear shafts, and steering components at production rates

METHOD SELECTION

Which Method for Steel Bores

📦

D < 20mm→ Gundrill

⚖

D 20–60mm→ BTA / ejector

⚡

>250 HB, long holes→ Pilot + BTA

🔧

Retrofit on lathe→ Ejector DTS

✅ Baseline: carbon & alloy steels are the reference material family for all deep hole methods — if you can prove a new method on steel, you can benchmark any other material against it.

SAFETY

Key Safety Points

⚠️ High-pressure coolant: 50–100 bar lines are lethal if disconnected under pressure. Relieve at the pump before maintenance; use whip-checks on every high-pressure hose.

🔥 Hot, sharp chips: steel deep holes produce long, hot ribbons and tight curls — use dedicated chip hooks, never pull chips by hand.

🛡️ Whip hazard: long gundrills must not free-spin above ~50 RPM — a whipping tube is a serious projectile risk.

Carbon & Alloy Steel

Material Properties & Speeds

Feed by Diameter

Key Data

Parameters & Best Practice

Achievable Ra (Published Data)

Strengths & Limitations

✅ Advantages

⚠ Limitations

Setup & Start-of-Cut

Where Carbon & Alloy Steel Deep Holes Are Drilled

Which Method for Steel Bores

Key Safety Points

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