Appearance
A 20-year-old deep hole drilling machine from a reputable manufacturer has better structural integrity — thicker castings, larger guideways, a heavier base — than many modern entry-level machines. Refurbishing an older machine restores its geometric accuracy to original specifications, upgrades the control system and coolant system to modern standards, and delivers a machine that drills as accurately as a new machine — at half the cost. But refurbishment requires knowing what to replace, what to recondition, and what to leave alone — and that depends on the brand.
Assessment
Refurbishment Decision Criteria
| Criterion | Refurbish | Replace | Notes |
|---|---|---|---|
| Machine age | 10–30 years | > 30 years (structural wear may be excessive) | Older than 30 years: replacement is usually more cost-effective |
| Structural condition | No cracks — no major casting damage — no severe way wear | Cracked castings — severely worn ways — twisted bed | Structural repairs are rarely economic |
| Spindle condition | Runout < 0.02 mm TIR at nose (can be rebuilt) | Runout > 0.05 mm — bearing journals worn — spindle bent | Spindle replacement may be expensive — evaluate cost |
| Way condition | Wear < 0.10 mm over full travel | Wear > 0.20 mm — deep scoring — edge breakdown | Re-grinding ways is possible if enough material remains |
| Guide bushing system | Standard bushing — parts available | Obsolete — no replacement bushings available | Bushing availability determines repairability |
| Coolant system | Can be upgraded — pump — piping — filtration | Integral design — cannot be separated | Most coolant systems can be upgraded independently |
| Control system | Can be retrofitted (CNC upgrade) | Obsolete proprietary control — no retrofit available | Modern CNC retrofit is common — but verify feasibility |
| Parts availability | Parts available from OEM or aftermarket | Proprietary parts obsolete — no alternative | Check parts availability for the specific brand before committing |
| Cost target | Refurbishment cost < 60% of new equivalent | Refurbishment cost > 60% of new | Include all costs: labor, parts, controls upgrade, coolant system |
Pre-Refurbishment Inspection
| Inspection Item | Method | Acceptance for Refurbishment | Notes |
|---|---|---|---|
| Bed level | Precision level | < 0.10 mm/m (can be corrected) | Re-level after foundation work — not a reason to scrap |
| Way straightness | Straightedge + feeler gauge | < 0.05 mm/m (can be re-ground) | Re-grinding is standard — verify sufficient material |
| Spindle runout | Dial indicator on taper | < 0.02 mm TIR (can be rebuilt) | Spindle rebuild is standard |
| Spindle-to-guideway parallelism | Dial indicator on test bar | < 0.01 mm per 100 mm (adjustable) | Adjustable through re-scraping or re-grinding |
| Coolant pump condition | Pressure test — flow test | Restorable with overhaul kit | Pump overhaul or replacement is standard |
| Hydraulic system | Pressure test — oil analysis | Restorable | Standard rebuild — new seals, valves, pump |
| Electrical system | Insulation test — component check | Upgradable | Full electrical modernization common |
Brand-Specific Considerations
| Brand | Typical Design Features | Common Wear Points | Parts Availability | Refurbishment Notes |
|---|---|---|---|---|
| Mollart (UK) | Mechanical gearbox drive — mechanical feed — simple robust design | Gearbox bearings — feed clutch — way surfaces — spindle bearings | Limited — some parts obsolete | Excellent candidate — simple mechanical design is easy to refurbish — CNC retrofit transforms capability |
| Precihole (India) | Modern design — linear guideways — AC servo drives — Siemens/Fanuc controls | Linear guide carriages — ball screws — spindle bearings — coolant seals | Good — OEM supports older machines | Refurbishment less common — newer machines — focus on spindle and coolant system |
| Unisig (USA) | Heavy-duty construction — box ways — dedicated gun drilling machines | Way surfaces — spindle bearings — guide bushing holder bore — coolant pump | Good — OEM supports older machines | Box way re-grinding is standard — excellent refurbishment candidate — heavy casting holds up well |
| TBT (Germany) | Precision construction — modular design — high-pressure coolant integral | Spindle assembly — coolant union seal — guide bushing system — hydraulic feed | Good — OEM supports older machines | High-precision refurbishment possible — requires skilled technicians for spindle work |
| BTA (Italy) | Robust construction — BTA drilling focus — large diameter spindles | Drill tube guide system — coolant seals — spindle drive | Moderate — some parts available | Tube guide system refurbishment is critical — requires specialized knowledge |
| Nagel (Germany) | Precision honing and drilling — integrated systems | Spindle — coolant filtration — bushing system | Moderate — specialist parts | Refurbishment requires OEM or specialized knowledge — not for general machine shop |
| Giddings & Lewis (USA) | Large horizontal drilling — floor-type or table-type | Way surfaces — spindle drive — coolant system | Limited — many G&L machines are large and custom | Structural reconditioning is main task — controls upgrade standard |
Disassembly and Inspection
| System | Disassembly | Key Inspection Points | Recondition Decision |
|---|---|---|---|
| Spindle | Remove from machine — disassemble bearings — remove drawbar — remove coolant union | Bearing journals (measure for wear) — spindle taper (check for damage) — thread condition — coolant union seal surface | Replace bearings (always) — re-grind taper if damaged — replace coolant union — recondition drawbar |
| Ways | Remove carriage — clean ways | Wear pattern (measure with straightedge) — scoring depth — edge condition — lubrication groove condition | If wear < 0.05 mm: re-scrape. If 0.05–0.20 mm: re-grind. If > 0.20 mm: evaluate viability |
| Ball screws | Remove — clean — measure backlash | Backlash (dial indicator) — nut condition — screw straightness — bearing condition | Replace if backlash > 0.05 mm — replace bearings always |
| Guide bushing holder | Measure bore with bore gauge | Bore roundness — bore diameter — alignment to spindle | Re-bore and bush if worn > 0.02 mm from spec |
| Coolant pump | Disassemble — inspect wear parts | Impeller clearance — wear ring condition — shaft seal — bearing condition | Rebuild with overhaul kit — or replace |
| Coolant tank | Drain — clean — inspect | Tank condition — internal baffles — drain — cover seals | Clean and repair — replace if corroded through |
| Hydraulic power unit | Drain — clean — inspect | Pump condition — valve function — cylinder seal condition — hose condition | Rebuild pump — replace seals — replace hoses |
| Electrical panel | De-energize — clean — inspect | Contactor condition — transformer condition — wire insulation — terminal condition | Modernize — replace safety relays — replace contactors — consider CNC retrofit |
Component Reconditioning
Spindle Rebuild
| Step | Action | Detail |
|---|---|---|
| 1 | Disassemble spindle completely | Remove bearings — remove drawbar — remove coolant union |
| 2 | Clean all components | Solvent clean — inspect for cracks — dye penetrant if needed |
| 3 | Measure bearing journals | Micrometer — compare to spec — if worn > 0.005 mm, grind and chrome plate or replace shaft |
| 4 | Measure spindle taper | Indicator — if runout > 0.002 mm at taper, re-grind in machine or on grinding attachment |
| 5 | Check drawbar | Measure length — check thread condition — check Belleville spring stack |
| 6 | Install new bearings | Per OEM — preload per spec — clean room assembly preferred |
| 7 | Measure assembled runout | At spindle nose: < 0.003 mm TIR. At 100 mm: < 0.005 mm TIR |
| 8 | Install new coolant union | New seal assembly — verify alignment |
| 9 | Run-in spindle | Low speed 30 minutes — gradual increase — check temperature at each speed |
Way Re-Grinding
| Step | Action | Detail |
|---|---|---|
| 1 | Set up machine on grinder | Portable grinder on bed — or move to surface grinder (if removable) |
| 2 | Verify reference surfaces | Use unworn surfaces as reference |
| 3 | Grind bed ways | Remove minimum material to clean up — typically 0.1–0.3 mm |
| 4 | Grind carriage ways | Match to bed ways — use same reference |
| 5 | Check alignment | Parallelism — straightness — squareness per OEM spec |
| 6 | Scrape for oil retention | Light scraping pattern — 15–25 spots per 25 mm² |
| 7 | Install new way wipers | Per OEM — seal against re-ground surfaces |
| 8 | Reassemble carriage | Adjust gibs — set clearance per spec |
Acceptance Testing
| Test | Method | Acceptance Criteria | Notes |
|---|---|---|---|
| Level — longitudinal | Precision level on bed ways | < 0.02 mm/m | After installation — before final alignment |
| Level — transverse | Precision level across bed | < 0.02 mm/m | — |
| Way straightness | Straightedge + feeler gauge | < 0.01 mm/m | After re-grinding |
| Spindle runout — at nose | Dial indicator on taper | < 0.003 mm TIR | After spindle rebuild |
| Spindle runout — at 100 mm | Dial indicator | < 0.005 mm TIR | — |
| Spindle-to-way parallelism — vertical | Dial indicator + test bar | < 0.005 mm per 100 mm | Critical for hole straightness |
| Spindle-to-way parallelism — horizontal | Dial indicator + test bar | < 0.005 mm per 100 mm | Critical for hole straightness |
| Guide bushing holder bore | Bore gauge | Within 0.01 mm of nominal | Re-bored if worn |
| Ball screw backlash | Dial indicator | < 0.02 mm | After reconditioning |
| Coolant pressure | Gauge at spindle | Per OEM spec ± 5% | After pump overhaul |
| Coolant flow | Flow meter | Per OEM spec ± 10% | — |
| Test part drilling | Drill test part to spec | Hole diameter ± 0.01 mm — surface finish Ra < 0.8 µm — straightness per spec | Final verification |
FAQ
When is it worth refurbishing a deep hole drilling machine instead of buying new?
Refurbishment is worth considering when: the machine has good structural integrity (heavy castings, box ways, rigid construction — typically machines from established brands like Mollart, Unisig, TBT) — these machines were built with 3–5× the structural mass of modern economy machines. The cost of refurbishment (spindle rebuild, way re-grinding, controls upgrade, coolant system modernization) is less than 60% of the cost of a new equivalent machine. The machine's geometry can be restored to original specifications (way re-grinding, spindle rebuild, alignment — these are standard procedures). The machine has parts availability (check with OEM or aftermarket suppliers for bearings, seals, bushings, ball screws, and control system components). The machine has a proven design and performance history (some older machines have features that are not available on modern machines — heavier construction, higher-pressure coolant systems, dedicated drilling cycles). Refurbishment is typically not worth it when: the machine has structural damage (cracked castings, twisted bed, severely worn ways with insufficient material for re-grinding). The brand is obsolete with no parts available. The cost estimate exceeds 60% of a new machine. The required precision exceeds the machine's original design capability.
What are the most important components to replace during a deep hole drilling machine refurbishment?
The most important components to replace during a refurbishment are: spindle bearings (always replace — regardless of measured condition — bearing condition determines spindle runout and drilling accuracy — use OEM-specified bearings or equivalent high-precision class (P4 or P2) angular contact bearings — preload per OEM spec). Coolant union seal assembly (always replace — the seal is the most common wear component in the entire machine — a new seal prevents coolant leakage into spindle bearings). Way wipers and seals (replace — old wipers are hardened and will score newly re-ground way surfaces). Ball screw bearings and preload (replace bearings — reset preload — adjust backlash). Guide bushings (replace or recondition — worn bushings directly affect hole size and straightness). All coolant hoses (replace — aged hoses can fail internally — releasing debris into the coolant system). Electrical contactors and relays (replace — age and cycling cause contact pitting — reliability issue). Hydraulic seals and hoses (replace — aged seals cause leaks and pressure loss). The one item that can often be retained rather than replaced: the coolant pump (most pumps can be rebuilt with a seal kit and bearing kit — replace only if the pump body or shaft is worn beyond spec).
Can an old mechanical deep hole drilling machine be retrofitted with CNC controls?
Yes — CNC retrofit is one of the most effective upgrades for an old deep hole drilling machine. The process: remove the existing mechanical feed system (gearbox, feed clutches, mechanical cams) and replace with servo motors and ball screws. Install a new CNC control (Siemens 828D or Fanuc Oi series are common choices — both support deep hole drilling cycles (peck drilling, deep drilling cycles with coolant control). Add new servo drives and motors (sized for the machine's feed forces — modern servo drives provide precise feed control that mechanical systems cannot match). The benefits: programmable peck cycles (all drilling cycles programmable — no mechanical cam changes). Precise feed control (servo feed provides 0.001 mm feed resolution — mechanical feed systems cannot match this). Automatic coolant pressure control (integrate coolant pump VFD control for pressure regulation during peck cycles). Tool life management (CNC tracks tool usage — alarms for tool change). Data collection (cycle times, production counts, alarms — available for OEE tracking). The cost of a CNC retrofit for a mechanical deep hole drilling machine is typically $20,000–$50,000 for control, servo drives, motors, ball screws, and installation — significantly less than a new machine.
How long does a deep hole drilling machine refurbishment take?
Typical refurbishment timeline: assessment and quotation — 1–2 weeks (inspect machine — measure wear — determine scope — obtain parts quotes — prepare quote). Parts procurement — 4–12 weeks (lead time for bearings, ball screws, seals, controls — long-lead items are spindle bearings and CNC control — order these first). Disassembly and inspection — 1–2 weeks (strip machine — clean — measure all components — confirm parts required). Way re-grinding — 1–2 weeks (if portable grinder on machine — or 2–3 weeks if machine must be moved to grinder). Spindle rebuild — 1 week (disassemble — inspect — repair — reassemble with new bearings — run-in). Controls retrofit — 2–4 weeks (install new CNC — wire servo drives — program — test). Coolant system modernization — 1–2 weeks (new pump if needed — new hoses — new filtration — tank cleaning). Reassembly and alignment — 2–3 weeks (reassemble — align spindle to ways — align bushing holder — set all clearances). Acceptance testing — 1 week (geometric accuracy verification — test part drilling — performance validation). Total typical timeline: 12–20 weeks for a complete refurbishment. The most time-consuming parts are parts procurement (waiting for bearings and controls) and way re-grinding (if the machine must be moved).
How much does a deep hole drilling machine refurbishment cost?
Cost ranges for deep hole drilling machine refurbishment: basic refurbishment (spindle rebuild, way re-grinding, coolant pump service, new seals and hoses — no controls upgrade) — $15,000–$40,000 depending on machine size and brand. Full refurbishment (spindle rebuild, way re-grinding, ball screw replacement, coolant system modernization, hydraulic system rebuild, electrical panel upgrade, alignment, test drilling) — $30,000–$80,000. Full refurbishment with CNC retrofit (all of the above plus removing mechanical feed system, installing servo motors and ball screws, new CNC control and drives, programming) — $50,000–$130,000. Cost breakdown typically: 20–30% labor (disassembly, reassembly, alignment, testing), 25–35% parts (bearings, seals, ball screws, bushings, hoses), 20–30% controls (CNC, servo drives, motors, wiring), 10–15% coolant system (pump, hoses, valves, tank service), 5–10% contingency (unexpected issues — always budget 10% contingency). Compared to new machine costs ($80,000–$500,000+ for a deep hole drilling machine), refurbishment at 40–60% of new offers significant savings. The best value is typically a mid-sized machine (10–20 years old) with good structural condition, receiving a full refurbishment including CNC retrofit.
Refurbishing a deep hole drilling machine is a cost-effective alternative to buying new — delivering 80–100% of new machine performance at 40–60% of the cost. The best candidates are machines from established brands (Mollart, Unisig, TBT, Precihole) with good structural condition and available parts. Key refurbishment tasks: spindle rebuild (always replace bearings), way re-grinding (restore geometric accuracy), guide bushing system reconditioning, coolant system modernization, and CNC retrofit (transform mechanical machines into modern precision drilling systems). Budget 12–20 weeks for a complete refurbishment and 40–60% of new machine cost. A properly refurbished machine can provide another 15–20 years of productive service. This article reflects industry practice as of 2026.