The quick reference for specifying a gundrill: standard diameter ranges from the major toolmakers, how drill length is calculated and written (d1 / l1 / l2), stock depth series, and the driver and coolant-hole options you need to put on an order.
Gundrill diameter ranges differ by construction type (solid carbide, brazed head, indexable). These are the published catalogue ranges:
| Maker / series | Construction | Diameter range | Notes |
|---|---|---|---|
| Gühring EB 100 | Solid carbide, single flute | Ø1.2–12 mm stock; Ø0.9–16 mm special | Flute length to 500 mm |
| Gühring EB 80 | Brazed carbide head | Ø3.97–22 mm stock; Ø2–40 mm special | Total length to 3,000 mm |
| Gühring ZB 80 | Two-flute | Ø2–22 mm | Cast iron & aluminum |
| Gühring EB 800 | Brazed carbide head | Ø12–24 mm stock; Ø12–52 mm special | Larger brazed series |
| botek Type 110 / 112 | Solid carbide tip (112 = step) | Ø1.850–51.200 mm | Max length 5,000 mm |
| botek Type 111 | Steel body, brazed blade + pads | Ø5.800–60.009 mm | — |
| botek Type 01 | Steel body, indexable inserts | Ø12.000–43.990 mm | On-machine insert change |
| botek Type 115 / 114 | Brazed head (115 drill / 114 trepan) | Ø2–51.2 mm (115); Ø11–50 mm (114) | — |
| ISCAR GD-DH | Indexable | Ø9.9–43.99 mm | Head lengths by diameter band |
| Mitsubishi MVS / MGS-MGD | Solid carbide | from Ø1.0 mm | Stock depths 2/7/12/20/25/30×D |
| Taegutec TRGD / TRGD3 | Indexable holder | Ø10–36 mm (to 40) | 10–25×D holders |
Manufacturer dimension tables use the same four letters (HARTNER example):
| Symbol | Meaning |
|---|---|
| d1 | Cutting diameter (mm or inch) |
| d2 | Shank diameter (h6 tolerance) |
| l1 | Overall length |
| l2 | Flute length |
| l3 | Shank/clearance section length |
Representative HARTNER single-flute (E 80) values:
| d1 (mm) | d2 h6 (mm) | l1 overall (mm) | l2 flute (mm) |
|---|---|---|---|
| 3.97 (5/32 in) | 10.0 | 230 | 185 |
| 10.00 | 20.0 | 400 | 350 |
| 12.70 (1/2 in) | 20.0 | 500 | 450 |
| 19.05 (3/4 in) | 32.0 | 715 | 650 |
| 25.40 (1 in) | 32.0 | 910 | 845 |
To order a gundrill for a specific hole, ISCAR’s formula sizes the flute and overall length:
| Symbol | Meaning | Typical value |
|---|---|---|
| N | Regrinding allowance (= carbide head length H − D) | varies with size |
| W | Hole depth to be drilled | your print |
| B | Chip-evacuation clearance behind the hole | 250 mm (gundrill machine); 2×D, min 15 mm (machining center) |
| F | Tool approach allowance | 10 mm |
| LA | Driver length | your driver (e.g. 70 mm) |
Worked example (ISCAR): drill a Ø10 mm hole 500 mm deep with a 25×70 mm driver. With N = (35−10) = 25 mm: L = 25 + 500 + 250 + 13 + 70 = 858 mm overall; flute length Ls = 25 + 500 + 250 = 770 mm.
Ex-stock gundrills are offered in fixed depth-to-diameter ratios, so the drill length tracks the hole L/D rather than absolute millimetres. A common solid-carbide stock series runs 2, 7, 12, 20, 25 and 30×D (Mitsubishi MVS example); specials extend far beyond. When ordering by ×D, always confirm whether the maker means flute length or overall length — they differ by the shank and driver.
Driver / shank types (ISCAR): central clamping surface (15°), frontal clamping surface, cylindrical with thread (M6–M24), VDI design, hexagonal, tapered, trapezoidal thread, and spray-mist types — pick the one that matches your machine’s driver or toolholder.
Coolant-hole designs (botek): a kidney-shaped coolant hole at small diameters, switching to 1-hole or 2-hole designs as diameter grows — flow capacity scales with the hole area, which is why small drills need much higher coolant pressure.