Center Drill Size Chart (#1–#6 & DIN 333) & Depth Calculator
A 60° combined drill and countersink (center drill) machines both the pilot clearance hole and the 60° conical seat for a lathe live center. Driving a #3 center drill to 70% cone fill produces a 5.28 mm cone mouth at programmed depth Z = −5.363 mm and spindle speed 1253 RPM.
60° Center Drill Dimensions Chart (#1–#6 & DIN 333) & CNC Z-Plunge Depth Calculator
Compute the exact CNC Z-axis plunge depth Z = 0.85·l1 + 0.3004·d1 + 0.8660·(Dmouth − d1) to seat a 60° lathe live center at 70% cone engagement without burying the tool past the 60° taper or snapping the pilot tip.
Center Drill vs. Spot Drill: Why 60° Center Drills Snap in CNC Milling
Combined drill-and-countersinks standardized under ASME Codes & Standards B94.11M, British Standards Institution (BSI) BS 328, and DIN German Institute for Standardization DIN 333 (ISO 866) are engineered specifically for turning between centers on a lathe or cylindrical grinder. The small pilot drill (d1) gives the point of the 60° tailstock center clearance at the bottom of the hole, while the 60° conical frustum supports the radial and axial cutting forces. If you only need to start a hole on a CNC machining center prior to twisting a 118° or 135° drill, do not use a fragile 60° center drill pilot—use a rigid 90° or 120° spotting tool sized in our spot drill depth and chamfer calculator.
When drilling lathe centers, the most common operator mistake is plunging past the top of the 60° cone into the cylindrical body D2 (beyond Zmax = −6.291 mm on a #3 tool). Beyond Zmax the cylindrical body D2 enters the hole and rubs the wall, so the tool is loaded on its cylindrical margin instead of the 60° cone.
| ANSI Size Designation | Body Diameter D2 | Pilot d1 × Length l1 | 70% Cone Mouth Ø | Target Z-Plunge (70% Cone) | HSS RPM (25 m/min) |
|---|---|---|---|---|---|
| #1 Combined (1/8" body × 3/64" pilot) | Ø0.1250" (3.175 mm) | Ø0.0469" (1.191 mm) × 1.19 mm | Ø2.58 mm (0.102") | Z = 2.57 mm (0.101") | 2506 RPM |
| #2 Combined (3/16" body × 5/64" pilot) | Ø0.1875" (4.763 mm) | Ø0.0781" (1.984 mm) × 1.98 mm | Ø3.93 mm (0.155") | Z = 3.96 mm (0.156") | 1671 RPM |
| #3 Combined (1/4" body × 7/64" pilot) | Ø0.2500" (6.350 mm) | Ø0.1094" (2.778 mm) × 2.78 mm | Ø5.28 mm (0.208") | Z = 5.36 mm (0.211") | 1253 RPM |
| #4 Combined (5/16" body × 1/8" pilot) | Ø0.3125" (7.938 mm) | Ø0.1250" (3.175 mm) × 3.18 mm | Ø6.51 mm (0.256") | Z = 6.54 mm (0.258") | 1002 RPM |
| #5 Combined (7/16" body × 3/16" pilot) | Ø0.4375" (11.113 mm) | Ø0.1875" (4.763 mm) × 4.76 mm | Ø9.21 mm (0.362") | Z = 9.33 mm (0.367") | 716 RPM |
| #6 Combined (1/2" body × 7/32" pilot) | Ø0.5000" (12.700 mm) | Ø0.2187" (5.556 mm) × 5.56 mm | Ø10.56 mm (0.416") | Z = 10.73 mm (0.422") | 627 RPM |
How Do You Calculate Exact Center Drill Z-Plunge Depth (Form A)?
The total Z-axis feed from tool tip touch-off on the faced shaft end is the sum of three geometric segments derived in Machinery's Handbook (31st Ed., Industrial Press):
1. 118° Pilot Point Height: htip = (d1 / 2) / tan(59°) = 0.30043 · d1 (also modeled in our drill point length calculator).
2. Effective Pilot Cylinder Length: 0.85 · l1 before the 60° taper transition begins.
3. 60° Conical Seat Depth: For a target cone mouth diameter Dmouth = d1 + (η / 100)(D2 − d1), the axial cone travel is zcone = (Dmouth − d1) / (2 · tan 30°) = 0.8660254 · (Dmouth − d1).
| DIN 333 Metric Size | Pilot d1 / Body D2 | Form A Z-Depth (60° Cone) | Max Safe Depth Zmax | Spindle Speed (25 m/min) |
|---|---|---|---|---|
| DIN 333 Form A 2.0 (5.0 mm body × 2.0 mm pilot) | Ø2.00 mm / Ø5.00 mm | Z = 4.54 mm (Ø4.10 mm) | Zmax = 5.32 mm | 1592 RPM (on D2) |
| DIN 333 Form A 2.5 (6.3 mm body × 2.5 mm pilot) | Ø2.50 mm / Ø6.30 mm | Z = 5.69 mm (Ø5.16 mm) | Zmax = 6.68 mm | 1263 RPM (on D2) |
| DIN 333 Form A 3.15 (8.0 mm body × 3.15 mm pilot) | Ø3.15 mm / Ø8.00 mm | Z = 7.20 mm (Ø6.54 mm) | Zmax = 8.46 mm | 995 RPM (on D2) |
| DIN 333 Form A 4.0 (10.0 mm body × 4.0 mm pilot) | Ø4.00 mm / Ø10.00 mm | Z = 9.09 mm (Ø8.20 mm) | Zmax = 10.65 mm | 796 RPM (on D2) |
Worked Examples: Programming #3, #4, and DIN 333 Form A 2.5 Lathe Centers
Worked Example 1 (#3 ANSI Combined Drill in 4140 Steel): Using a #3 center drill at 70% cone fill and Vc = 25 m/min, our engine calculates pilot tip + cylinder travel 2.36 + 0.83 = 3.20 mm plus 60° cone travel 2.17 mm for a total programmed depth of Z = −5.363 mm (−0.2111"), producing a 5.28 mm bearing cone mouth at 1253 RPM. Use our G83 peck drilling cycle calculator with a Q1.5 peck to clear chips from the pilot.
Worked Example 2 (#4 Center Drill & DIN 333 Form A 2.5): For a precision ground spindle shaft using a #4 center drill (d1 = 3.175 mm, D2 = 7.938 mm), the 70% cone mouth is 6.51 mm. On metric prints specifying DIN 333 - A 2.5, program Z = −5.690 mm at 1263 RPM.
The size codes come from ASME Codes & Standards B94.11M (ANSI #1 to #6) and from International Organization for Standardization (ISO) ISO 866, the international basis of DIN 333 (Form A sizes R2.0 to R4.0). Pick the size whose pilot diameter suits the shaft end and whose body diameter leaves room for the 60° cone, then confirm the depth with the calculator above before programming the drill.
After the first center drill pass, check the pilot with pin gages and the 60° seat with a 60° center gage or a go/no-go plug at the cone mouth. If the cone sits deeper than the programmed Z, stop, correct the depth, and recheck before the center is loaded, because a cone that passes the body diameter D2 weakens the bearing surface.
Cite this page
ToolSpecVault Engineering Data Team. (2026, November 2). Center Drill Size Chart (#1–#6 & DIN 333) & Depth Calculator. ToolSpecVault. https://toolspecvault.com/center-drill-size-chart-60-degree-depth-calculator/