18.0 mm drill size
A 18.0 mm metric drill is 0.7087 in (18.000 mm). It is the cut tap, 75% thread drill for M20x2.
- Decimal inch
- 0.7087
- Millimeters
- 18.000
- Nearest 1/64
- 45/64" (+0.0055)
- Type
- metric drill
Nearest equivalents in other systems
Speeds and feeds: in mild steel an HSS drill starts at about 490 RPM and 0.0113 in/rev (5.54 IPM); in 6061 aluminum about 1,350 RPM.
18.0 mm drill speeds and feeds by material
Jobber-length twist drill, D = 0.7087 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 | 1,350 | 600 | 3,230 | 0.0108 | 14.6 | 34.9 |
| Brass / free-machining | 150 | 810 | 400 | 2,160 | 0.0089 | 7.21 | 19.2 |
| Low-carbon steel (1018) | 90 | 490 | 300 | 1,620 | 0.0113 | 5.54 | 18.3 |
| Alloy steel (4140, annealed) | 70 | 380 | 250 | 1,350 | 0.0119 | 4.52 | 16.1 |
| Stainless 304 | 40 | 220 | 150 | 810 | 0.0093 | 2.05 | 7.53 |
| Gray cast iron | 80 | 430 | 250 | 1,350 | 0.0098 | 4.21 | 13.2 |
| Titanium 6Al-4V | 25 | 130 | 100 | 540 | 0.0054 | 0.70 | 2.92 |
| Plastics (acetal) | 300 | 1,620 | 500 | 2,700 | 0.0068 | 11.0 | 18.4 |
Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 490 RPM × 0.287 mm/rev = 141 mm/min.
Worked example: 18.0 mm drill in 1018 steel
- HSS drill in low-carbon steel: 90 SFM.
- RPM = 3.82 × 90 ÷ 0.7087 ≈ 490 RPM.
- Feed for a 0.709 in drill in mild steel ≈ 0.0113 in/rev.
- IPM = 490 × 0.0113 = 5.54 IPM.
Peck cycle by hole depth
| Depth | Cycle | Peck | Note |
|---|---|---|---|
| 3×D = 2.126 in (54 mm) | G81 (no peck) | None | Up to 3×D a sharp drill clears chips on its own. |
| 5×D = 3.543 in (90 mm) | G73 chip-break | 1 × D | Chip-break pecks; full retract if chips pack (soft aluminum, stainless). |
| 8×D = 5.669 in (144 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 18.0 mm drill
- M20x2 — cut tap, 75% thread
Nearest drills
- 45/64": 0.7031 in / 17.859 mm (-0.0055 in)
- 17.75 mm: 0.6988 in / 17.750 mm (-0.0098 in)
- 18.25 mm: 0.7185 in / 18.250 mm (+0.0098 in)
- 23/32": 0.7188 in / 18.256 mm (+0.0101 in)
Common questions
- What is a 18.0 mm drill in decimal and mm?
- 0.7087 in, or 18.000 mm; nearest fractional drill: 45/64" (0.7031 in, -0.0055 in); nearest number / letter drill: Letter Z (0.4130 in, -0.2957 in).
- What RPM for a 18.0 mm drill in steel?
- In low-carbon steel (1018) an HSS 18.0 mm drill (0.7087 in) runs about 490 RPM at 90 SFM; a carbide drill about 1,620 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
- What feed for a 18.0 mm drill?
- About 0.0113 in/rev in mild steel, 0.0108 in/rev in aluminum and 0.0093 in/rev in 304 stainless. At 490 RPM that is 5.54 IPM in steel (IPM = RPM × IPR).
- What RPM for a 18.0 mm drill in aluminum?
- 1,350 RPM with HSS (250 SFM) or up to 3,230 RPM with carbide (600 SFM), feeding about 0.0108 in/rev.
- What tap uses a 18.0 mm drill?
- M20x2 (cut tap, 75% 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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