3.1 mm drill size
A 3.1 mm metric drill is 0.1221 in (3.100 mm). It is the cut tap, 50% thread drill for M3.5x0.6.
- Decimal inch
- 0.1221
- Millimeters
- 3.100
- Nearest 1/64
- 1/8" (-0.0029)
- Type
- metric drill
Nearest equivalents in other systems
Speeds and feeds: in mild steel an HSS drill starts at about 2,820 RPM and 0.0029 in/rev (8.18 IPM); in 6061 aluminum about 7,820 RPM.
3.1 mm drill speeds and feeds by material
Jobber-length twist drill, D = 0.1221 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.
| Material | HSS SFM | HSS RPM | Carbide SFM | Carbide RPM | Feed (in/rev) | HSS IPM | Carbide IPM |
|---|---|---|---|---|---|---|---|
| Aluminum (6061) | 250 | 7,820 | 600 | 18,780 | 0.0028 | 21.9 | 52.6 |
| Brass / free-machining | 150 | 4,690 | 400 | 12,520 | 0.0023 | 10.8 | 28.8 |
| Low-carbon steel (1018) | 90 | 2,820 | 300 | 9,390 | 0.0029 | 8.18 | 27.2 |
| Alloy steel (4140, annealed) | 70 | 2,190 | 250 | 7,820 | 0.0029 | 6.35 | 22.7 |
| Stainless 304 | 40 | 1,250 | 150 | 4,690 | 0.0020 | 2.50 | 9.38 |
| Gray cast iron | 80 | 2,500 | 250 | 7,820 | 0.0018 | 4.50 | 14.1 |
| Titanium 6Al-4V | 25 | 780 | 100 | 3,130 | 0.0015 | 1.17 | 4.70 |
| Plastics (acetal) | 300 | 9,390 | 500 | 15,650 | 0.0049 | 46.0 | 76.7 |
Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 2,820 RPM × 0.074 mm/rev = 208 mm/min.
Worked example: 3.1 mm drill in 1018 steel
- HSS drill in low-carbon steel: 90 SFM.
- RPM = 3.82 × 90 ÷ 0.1221 ≈ 2,820 RPM.
- Feed for a 0.122 in drill in mild steel ≈ 0.0029 in/rev.
- IPM = 2,820 × 0.0029 = 8.18 IPM.
Peck cycle by hole depth
| Depth | Cycle | Peck | Note |
|---|---|---|---|
| 3×D = 0.366 in (9.3 mm) | G81 (no peck) | None | Up to 3×D a sharp drill clears chips on its own. |
| 5×D = 0.610 in (15.5 mm) | G73 chip-break | 1 × D | Chip-break pecks; full retract if chips pack (soft aluminum, stainless). |
| 8×D = 0.976 in (24.8 mm) | G83 full retract | 0.5-1 × D, shrinking with depth | Retract to clear chips; reduce feed ~10-20% past 5×D. |
Taps that use a 3.1 mm drill
- M3.5x0.6 — cut tap, 50% thread · tap speeds and feeds
Nearest drills
- #31: 0.1200 in / 3.048 mm (-0.0021 in)
- 1/8": 0.1250 in / 3.175 mm (+0.0029 in)
- 3.2 mm: 0.1260 in / 3.200 mm (+0.0039 in)
- 3.0 mm: 0.1181 in / 3.000 mm (-0.0039 in)
Common questions
- What is a 3.1 mm drill in decimal and mm?
- 0.1221 in, or 3.100 mm; nearest fractional drill: 1/8" (0.1250 in, +0.0029 in); nearest number / letter drill: #31 (0.1200 in, -0.0021 in).
- What RPM for a 3.1 mm drill in steel?
- In low-carbon steel (1018) an HSS 3.1 mm drill (0.1221 in) runs about 2,820 RPM at 90 SFM; a carbide drill about 9,390 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
- What feed for a 3.1 mm drill?
- About 0.0029 in/rev in mild steel, 0.0028 in/rev in aluminum and 0.0020 in/rev in 304 stainless. At 2,820 RPM that is 8.18 IPM in steel (IPM = RPM × IPR).
- What RPM for a 3.1 mm drill in aluminum?
- 7,820 RPM with HSS (250 SFM) or up to 18,780 RPM with carbide (600 SFM), feeding about 0.0028 in/rev.
- What tap uses a 3.1 mm drill?
- M3.5x0.6 (cut tap, 50% thread).
Nearby drill sizes
Sources
- Machinery's Handbook, 31st ed., Speeds and Feeds for Drilling, Reaming and Threading (Tables 17-23) — HSS and carbide drilling SFM (rounded).
- RedLine Tools (Productivity Inc.) catalog p. 340, Cobalt & HSS Drills Speeds & Feeds — feed per rev by drill diameter and material (middle of the catalog range).
- ASME B94.11M twist drills: number (#1-#80) and letter (A-Z) drill sizes; drill size reference.
Material feed multipliers (aluminum 1.3×, brass 1.1×, 4140 0.85×, stainless and titanium 0.7× the mild-steel feed) are JobLine estimates. Peck guidance is JobLine shop practice. Use your drill maker's data first.
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