Micro Gun Drilling 0.5–2 mm
Micro gun drilling is the specialty end of the process — holes down to 0.5 mm diameter, drilled to depth ratios that conventional drilling cannot approach. It appears in cannulated bone screws, surgical instruments, fuel injector spray holes, mold ejector-pin holes, and precision electronics. At these diameters the tool is effectively a needle with an oil channel through it, and the engineering that makes a 20 mm hole routine does not simply shrink — it changes.
This guide covers the parameters, machine requirements, and failure modes of gun drilling 0.5–2 mm holes.
What Changes Below 2 mm
| Factor | Ø10 mm gun drilling | Ø1 mm micro gun drilling |
|---|---|---|
| Tool stiffness | Stiff enough to self-pilot | Needle-thin; bends and whips |
| Coolant channel | ~2–3 mm bore | ~0.2–0.4 mm bore |
| Coolant pressure | 60–120 bar | 200–300+ bar |
| Feed | 0.020–0.040 mm/rev | 0.002–0.006 mm/rev |
| Alignment tolerance | Forgiving | Spindle runout under 0.005 mm |
| Typical machine | Gun drilling machine, lathe retrofit | High-RPM precision machine, Swiss lathe |
The core problem is that everything is small — the oil channel, the flute, the chips, and the margin for error. The same mistakes that shorten tool life at 10 mm break the tool instantly at 1 mm.
Cutting Parameters
Speeds and feeds are starting points; the chips must break into tiny C-segments that flow out of the flute without packing.
| Drill diameter | Speed (m/min) | RPM (approx.) | Feed (mm/rev) | Coolant pressure |
|---|---|---|---|---|
| 0.5 mm | 15–30 | 10,000–20,000 | 0.001–0.004 | 300+ bar |
| 1.0 mm | 20–40 | 6,000–13,000 | 0.002–0.006 | 250–300 bar |
| 1.5 mm | 25–50 | 5,000–11,000 | 0.003–0.008 | 200–300 bar |
| 2.0 mm | 30–60 | 5,000–10,000 | 0.004–0.010 | 150–250 bar |
Run at the lower end of the speed range on the first part. At micro scale, tool failure is fast — a mis-set feed or a dwell in the cut snaps the tip in a heartbeat.
Depth and Straightness
Micro gun drills reach the highest depth ratios in the process family. Advertised capability runs to 300:1 and beyond; practical production is typically 50–150:1 depending on diameter, material, and machine class.
Straightness is held to the same benchmark as larger holes — about 0.08 mm per 300 mm on a properly aligned machine — but it is harder to achieve because the tool has no stiffness to resist lateral forces. Guide bushings and whip guides are not optional at this scale. For the depth-ratio framework, see maximum L/D by method.
The Five Things That Make or Break Micro Gun Drilling
- Alignment. Spindle to bushing concentricity within ~0.005 mm and spindle runout as low as possible. A few micrometers of misalignment is the difference between a straight hole and a broken drill. See setup and alignment.
- Coolant. Pressure at the tip matters more than the pump gauge; filter to 5–10 µm. A single hard particle in a 0.3 mm oil channel blocks it and starves the edge. See coolant filtration.
- Feed. Constant and uninterrupted. Never dwell in the cut; the work-hardened zone chips the tip on restart.
- Tool quality. A micro gun drill is a precision instrument — ground geometry, sharp edge, and regrind before wear shows. Regrinding discipline matters more than at large diameters.
- Workpiece support. Long parts need steady rests or counter-rotation; the workpiece must not whip the needle-thin tool.
Machines for Micro Gun Drilling
| Machine type | Suitability |
|---|---|
| Dedicated micro gun drilling machine | Best — precision spindles, high pressure, whip control, depth to 150:1+ |
| Swiss-type lathe with gun drilling attachment | Common for bone screws and small cylindrical parts; see Swiss lathe deep hole drilling |
| Precision machining center with micro head | Works for shorter holes with a rigid spindle and guide bushing |
Whatever the machine, high pressure (200 bar or more) and high spindle speed (10,000–20,000 RPM for 0.5–1 mm) are the two requirements that filter out ordinary machines.
Chip Control at Micro Scale
Chips break by feed — if the feed is too low, a continuous ribbon packs the tiny flute and jams the drill. The chip-breaker grind on a micro drill is proportionally more important. Watch the chip color and shape: short, light-straw C-segments at consistent flow are the target. A flash of blue or an interrupted chip stream means the parameters are drifting.
For the general chip-shape diagnostic, see the chip morphology guide.
Common Problems
| Problem | Cause | Fix |
|---|---|---|
| Drill breaks at entry | Misalignment or burr at start | Align spindle and bushing; deburr the entry |
| Chips pack the flute | Feed too low or coolant starved | Raise feed; verify pressure at tip and filtration |
| Hole drifts off-center | Spindle runout or bushing wear | Reduce runout; replace bushing |
| Tool whips at depth | No guide support on long holes | Add whip guides or counter-rotation |
| Blue chips / overheating | Speed too high or dwell | Reduce speed; keep feed constant |
FAQ
How small can gun drilling go? Production micro gun drilling handles down to about 0.5 mm diameter; specialized setups go below that. The practical production depth ratio is 50–150:1.
What coolant pressure does micro gun drilling need? 200–300+ bar for 0.5–2 mm holes — higher than larger-diameter gun drilling, because the oil channel and chip annulus are tiny.
Why do micro gun drills break so easily? At 1 mm the tool is a needle. Misalignment, a dwell, a hard particle in the coolant, or a chip-packed flute snaps the tip — the margin for error is micrometers.
Can micro gun drilling be done on a normal machining center? Short holes can work on a rigid machine with a micro head, guide bushing, and high-pressure coolant. For 50:1 and beyond, a dedicated machine or Swiss-type lathe is the reliable choice.
Where is micro gun drilling used? Medical (cannulated bone screws, instruments), fuel injectors, mold ejector pins, and precision electronics. See medical implant drilling for the application view.
Summary
Micro gun drilling for 0.5–2 mm holes is the same process as large-diameter gun drilling, but with every margin shrunk to micrometers. It demands high spindle speed, 200–300 bar coolant filtered to 5–10 µm, precise alignment, constant feed, and disciplined tool care. Done right it produces 50–150:1 holes in single-lip, needle-thin tools — the enabler behind bone screws, injectors, and precision micro components.
For speeds and feeds across materials, see gun drilling speeds and feeds. For parameters that change with depth, see depth ratio adjustments.