The best machine is not the most expensive one — it is the one matched to the process requirements of your dominant products. Define the hole, choose the method, then size the machine: spindle power, coolant pressure and flow, work envelope, feed thrust, and accuracy class. Dedicated machines, CNC retrofits, and combination systems each earn their place.
A purpose-built deep hole drilling machine (gundrill or BTA) delivers the highest rigidity, straightness, and duty cycle. Costs more, but the process is engineered around chip evacuation, coolant, and steady rests — no compromises.
An ejector (two-tube) or extended-drill system retrofits onto an existing lathe, boring mill, or machining center. Lower entry cost and high flexibility, but L/D is limited to roughly 30:1 and it still needs a high-horsepower spindle plus a high-pressure, high-volume coolant system.
| Decision Dimension | Dedicated Machine | Retrofit (Ejector / Extended Drill) | Combination Machine |
|---|---|---|---|
| Entry cost | $50k–$1M+ depending on class | $30k–$100k kit + base machine | $150k–$600k |
| Typical L/D | Up to 300:1 (gundrill), 200:1 (BTA) | ≤ 100:1 in practice, ~30:1 on CNC retrofit | Depends on selected method |
| Max depth | Up to 12 m standard, 20 m+ special | ≤ 1.5 m on most retrofits | Up to 3–6 m |
| Diameter range | 0.5–500 mm depending on type | Ø18–250 mm (ejector) | 8–65 mm (changeover machines) |
| Straightness class | Highest — counter-rotation available | Moderate | High |
| Changeover between methods | Fixed to one method family | Fixed to ejector | 10–60 minutes between gundrill and BTA |
| Best for | Long bores, high production, tight straightness | Job shops, small batches, multi-variety parts | Mixed portfolios, prototyping plus production |
Every deep hole drilling machine fits one of five archetypes. Match the archetype to your dominant hole geometry before you compare brands.
| Type | Applicable Process | Diameter | Depth Capacity | Accuracy | Reference Price |
|---|---|---|---|---|---|
| Gundrill dedicated machine | Gundrilling (single-lip / ELB) | Ø0.5–50 mm | ≤ 3 m (up to 6 m special) | High | $50k–150k |
| BTA dedicated machine | BTA / STS, trepanning, pull boring, bottle boring | Ø12–250+ mm | ≤ 12 m (up to 20 m special) | High | $100k–500k+ |
| Ejector retrofit | Ejector (double-tube) drilling, extended drill | Ø18–250 mm | ≤ 1.5 m | Moderate | Depends on base machine |
| Combination machine | Gundrill + BTA on one machine | Ø8–65 mm typical | ≤ 3 m, 100:1 or greater | High | $150k–600k |
| Horizontal / vertical special | Gundrill, BTA, skive & roller burnish, multi-spindle | Ø0.8–500 mm | Horizontal ≤ 6 m (20 m custom); vertical ≤ 2 m | Highest | $150k–600k+ |
These six numbers define 90% of machine selection. Everything else is negotiable.
| Parameter | Why it matters | Typical Range | How to verify |
|---|---|---|---|
| Max bore diameter & depth | Defines machining range; the single most important number | Gundrill Ø1–50 mm; BTA Ø12–250+ mm | Machine brochure range vs. your longest part |
| Spindle power | Insufficient power caps feed rate and stalls on hard material | 7.5–30 kW gundrill; 15–100+ kW BTA | Calculate net power from toolmaker cutting-force charts |
| Max spindle speed | Small-diameter gundrills need 7,000–12,000+ rpm | 4,000–20,000 rpm | Speed at the drilling spindle, not the milling spindle |
| Coolant pressure | Drives chip evacuation; <50 bar on Ø10 mm causes clogging | Gundrill 50–150+ bar; BTA 15–100 bar | Live gauge test under full flow |
| Coolant flow rate | Volume removes heat; a Ø20 mm BTA bit needs ~150 L/min | 10–800 L/min depending on method | Flow meter at the tool head |
| Filtration level | >20 μm particles cause abrasive wear and blocking | ≤10–50 μm by method | Filter rating + particle-count test |
| Feed / axis thrust | Must handle cutting force without deflection | Typically 2–5× expected thrust | Axis thrust rating on the datasheet |
| Workpiece weight capacity | Heavy parts require between-center or steady-rest support | 1–30 t depending on class | Max weight between centers vs. with steadies |
| Counter-rotation | Rotating part opposite the tool cancels radial deviation | Standard on most center-drilling machines | Check option list — often omitted on cheap units |
| Automation | Load/unload, ATC, pallet changer, chip conveyor | Optional on nearly all machines | Interface with your existing cells |
Work the numbers before you talk to a sales engineer. Six steps turn a product portfolio into a machine requirement.
List every part you will drill: bore diameter, depth, material, batch size, tolerance. Sort by revenue — the machine must fit your dominant products, not your biggest outlier.
Rule of thumb: gundrill below Ø20–30 mm, BTA above Ø20 mm where metal removal rate matters, ejector when you must use existing equipment. Depth ratio L/D decides further.
Use the material guide for Vc and feed, compute metal removal rate, then net power from the toolmaker’s cutting-force charts. Add a 30–50% service factor — underpowered spindles stall on hardened material.
Match pressure and flow to the drill diameter. A Ø20 mm BTA bit needs ~150 L/min. High-end systems reach 170 bar. Check oil temperature control — above 50°C, thermal expansion destabilizes holes deeper than 5 m.
Horizontal for long shafts and high production, vertical for small precision holes and tight floor space, CNC retrofit for variety and prototyping. Steady rests every 800–1,000 mm suppress whip on bores over 1 m.
Below ~200 pcs/month a manual machine is fine. Above it, budget for automatic load/unload, tool monitoring, chip conveyor, and coolant filtration — the auxiliary systems often cost as much as the machine.
| Process Method | Pressure Range | Flow Rate Range | Filtration Requirement | Coolant Type |
|---|---|---|---|---|
| Gundrilling (< Ø10 mm) | 80–150 bar | 10–40 L/min | < 10 μm | Oil or high-concentration emulsion |
| Gundrilling (Ø10–50 mm) | 50–120 bar | 40–100 L/min | < 20 μm | Oil or emulsion |
| BTA / STS (Ø12–70 mm) | 15–100 bar | 100–400 L/min | < 50 μm | Emulsion or oil |
| Ejector / DTS (Ø20–250 mm) | 10–50 bar | 200–800 L/min | < 100 μm | Emulsion standard |
| Configuration | Pros | Cons | Best For |
|---|---|---|---|
| Horizontal | Best rigidity, long stroke, gravity chip evacuation, virtually unlimited workpiece length | Large floor space, higher cost, coolant return requires trench or pump | Shafts, long bores (bars, cylinders), high production |
| Vertical | Small footprint, gravity assists alignment, no coolant return pump needed | Limited stroke (typically ≤2 m), not for very long holes, workpiece height restricts ceiling | Precision small holes, valve bodies, limited floor space |
| CNC retrofit | Highest flexibility, leverages existing equipment investment | L/D limited to ~30:1, needs ≥70 bar coolant system added, reduced rigidity vs. dedicated | Small batches, multi-variety, job shops, prototype work |
For bores beyond 1,000 mm, hydraulic stabilizing brackets (shock pads) installed at 800–1,000 mm intervals suppress drill-pipe whipping — the main cause of bore deviation. Clamping pressure of 15–20 bar on the pads prevents the tube from dancing. Cast-iron or welded-steel beds with linear guideways, preloaded ballscrew or rack-and-pinion drives, and high-precision thrust bearings separate a deep hole machine from a converted lathe.
| Tier | Example Machines | Price Range | Capability | Notes |
|---|---|---|---|---|
| Entry gundrill | Basic CNC gundrill (India / China) | $24k–$40k | Ø5–35 mm, ~1–2 m depth | Prices exclude shipping, installation, rigging, tooling |
| Mid 3-axis CNC gundrill | Jiayong JZC12-2, Shenzhen Joint TS2120 / DH-800, Temy DHD-850 | $40k–$80k | Ø2.5–30 mm, 800–1,000 mm depth | The workhorse tier for small job shops |
| BTA / heavy duty | Schnell SBM125 (India), Zonjet BTA | $60k–$100k | Ø30–125 mm, up to 10 m depth | 51 kW tool spindle, 750 L/min coolant |
| Multi-functional 5-axis | Temy U8-5Axis vertical cradle | $115k–$130k | Drill + mill + tap in one setup | Tool library, ATC, pallet options |
| High-end dedicated | UNISIG (UNE / UNI / B-series), TBT (ML / M series) | $500k–$1M+ | Ø0.8–500 mm, up to 12–20 m | Counter-rotation, automation, 216 HP B700-6M class |
A sound mechanical machine from the 1990s with a new control is often a smarter buy than an entry-level new machine — the iron is the expensive part.
| Machine | Retrofit | Result |
|---|---|---|
| Wohlenberg B 1000 deep hole drill | Siemens 840D SL control, rebuilt 2014 | Ø1,000 mm workpiece, 4,500 mm drilling depth, 110 kW spindle — oil & gas service |
| IMSA MF1000B2 gundrill | Heidenhain TNC620 with gundrilling cycles, LAN + remote support | Ø4–20 mm, 1,000 mm depth, revamped by the manufacturer |
| Toshiba horizontal CNC drill (1986) | Fecken-Kirfel: new control, switch cabinet, ERP connectivity; mechanicals kept | State-of-the-art capability at a fraction of new cost, less downtime than a new install |
Price is the last differentiator, not the first. Evaluate vendors on process support, spare-parts depth, and how fast they answer a tooling question at 2 a.m.
| Vendor | Country | Focus & Representative Capability |
|---|---|---|
| UNISIG | USA | High-end dedicated systems. UNE gundrill (to Ø40 mm, 12,000 rpm, 2,000+ psi coolant); UNI-50BTA combination (8–65 mm, 100:1, ~10-min changeover); B-series BTA to Ø300 mm, 2–6 m, 216 HP B700-6M class, counter-rotation |
| TBT (Tiefbohrtechnik) | Germany | Global market leader. ML series all-rounder, 1–6 spindles, Ø0.8–400 mm, depths past 12 m; M-series single-spindle with CNC |
| Mollart Engineering | UK | Custom deep hole machines, exclusive UK partner of Botek tooling; MD-BTA series does gundrill + BTA on one machine |
| Botek | Germany | Deep hole tooling (gundrills, BTA heads, ejector drills, Ø0.5–500 mm) plus machine retrofit solutions |
| Precihole | India | Ø1–250 mm, depth to 10 m, strong value in the mid range |
| Kays Engineering | UK | Custom deep hole machines; among the global top 5 by market share |
| Entrust / TechniDrill | Global | Specialized deep hole machine builders serving the world market |
| Sunnen | USA | Leader in skive & roller burnishing and honing equipment — the finishing partner to a deep hole line |
| Regional value suppliers | Italy / China | Galbiati Group, Honge Precision, Dezhou Guanlu / Jutai — cost-effective solutions for standard configurations |
| If your dominant part looks like… | Choose… | And demand… |
|---|---|---|
| Firearm barrel / fuel injector, Ø3–15 mm, L/D > 50:1 | Vertical gundrill machine | 7,000+ rpm, 50–150 bar coolant, ≤10 μm filtration |
| Hydraulic cylinder barrel, Ø30–125 mm, 1–10 m | Horizontal BTA machine | ≥30 kW spindle, 150–750 L/min flow, steady rests |
| Mold plate waterlines, Ø8–20 mm on existing MC | Ejector retrofit | ≥70 bar coolant system, guide bushing, pilot-hole procedure |
| Landing gear / transmission, both gundrill & BTA bores | Combination machine (e.g., UNI-50BTA class) | Rapid changeover, counter-rotation, torque monitoring |
| Oil & gas downhole tool, Ø100–300 mm, > 6 m | Heavy BTA / trepanning special | 100+ kW, rack-and-pinion feed, 9+ t workpiece capacity |
| # | Mistake | Consequence | Fix |
|---|---|---|---|
| 1 | Choosing the method first, then ignoring diameter limits | Gundrill forced above Ø40–50 mm loses productivity; BTA below Ø12 mm loses chip clearance | Let diameter and L/D pick the method |
| 2 | Undersizing the coolant system | Chip clogging, tool failure, surface scoring — even on a rigid machine | Buy coolant capacity first; pressure & flow per method chart |
| 3 | Buying on price per machine, not cost per hole | The cheapest machine fails the tolerance test on your parts | Model tooling, coolant, scrap, and setup across 5 years |
| 4 | Ignoring work envelope and workpiece weight | Part does not fit between centers or overwhelms the table load | Verify max bore depth, swing, and steadies against your largest part |
| 5 | Specifying a converted lathe as a “deep hole machine” | No pressure head, weak coolant, no steady rests — drift and vibration | Demand steady rests, pressure head, and guided feed on any BTA retrofit |
| 6 | Overlooking alignment and calibration | Straightness drift that shows up as scrap 1,000 mm deep | Plan a manufacturer alignment check and re-certification schedule |
| 7 | Assuming the machine runs itself | No tool monitoring, no coolant-pressure monitoring, no process records | Specify instrumented monitoring and automated retract on threshold |