Here’s a “factory-floor to your shop” guide for evaluating a used / surplus TRAUB TNK 36 CNC lathe / turning center (also sometimes referenced as TNK 28/36 variants). I’ll include known specs (as reference baselines), then walk through what to check, how to test it, red flags, and negotiation tips.

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0. Reference — What is a TRAUB TNK 36?

Before inspection, gather baseline specs so you know where the “slack” is tolerable vs unacceptable. Based on various used-machine listings and catalogs:

Spec	Typical / Advertised Value	Notes / Source
Max bar / workpiece diameter	~ 36 mm	“Machining diameter max: 36 mm” listed
Spindle speed	~ 6,300 rpm	Multiple listings show this (main and counter spindle)
Spindle power (main & counter)	~ 10.7 kW	From listing
Number of axes	~ 9 axes (in many Swiss / multi-axis configurations)
Turret / tool stations	12 positions / fully motorized / driven tooling (for many units)
X / Z travel	~ 370 mm (X), ~ 250 mm (Z) for the main cutting axes
Machine footprint / weight	~ 3,335 × 1,222 (mm floor space), height ~1,680 mm, ~ 4,000 kg weight listed in some ads
Control / electronics	TRAUB TX8i in many cases

These specs act as your “gold standard” — when you inspect the used machine, deviations from these (or worse) will help you assess wear, modifications, or damage.

Also note: the TNK line is often used for automatic bar-fed / “Swiss-style” turning tasks (i.e. smaller diameters, higher axis count, multitasking).

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1. Pre-visit Preparation & Documentation Requests

Before you travel, ask the seller or current operator for as much of this as possible:

1. Service / maintenance / repair logs
   • Past spindle rebuilds, bearing replacements, guideway rework, turret overhauls
   • Frequency & dates of calibration checks
2. Configuration & options listing
   • Which axes, live tooling, sub-spindle(s), back machining, Y-axis (if any)
   • Type of turret(s), number of tool stations, driven tool power, tool speeds
3. Control / electronics documentation
   • Control model and version (e.g. TX8i), I/O lists, wiring diagrams, backups, parameter files
   • Spare modules, replacement parts for drives, encoders
4. Operating / power-on hours
   • Total hours, cutting vs idle
   • Duty cycles (how heavily loaded)
5. Spare parts / tooling inventory
   • Turret tooling, live tools, collets, holders, bar feeders, etc.
6. Video / photo evidence of motion
   • Axes moving, turret indexing, spindle turning, tool change cycles
7. Alignment / accuracy check reports
   • Past records of straightness, backlash, thermal drift
8. Transport / rigging plan
   • How they will dismantle, ship, reassemble, realign
9. Control backups / parameter / memory retention
   • Are all original parameters, programs, settings intact and backed up?

Having this ahead of time lets you tailor your on-site benchmarking and focus on suspect areas.

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2. On-Site Inspection & Testing Checklist

Bring precision tools (dial indicators, test bars, feeler gauges, gauges, vibration meter if available). A methodical walk-through is crucial:

A. Mechanical / Structural

• Base / frame / castings
  • Check for cracks, weld repairs, distortions, signs of rework
  • Surface corrosion, but structurally intact foundation
• Guideways / slides / linear ways
  • Inspect for wear bands, scratches, pitting, uneven wear
  • Move carriages at different speeds and directions, feel for binding, stiction, jumps
• Lead screws / ball screws / feeds
  • Uncover covers and inspect threads, check for wear
  • Measure backlash / lost motion in each axis
• Spindles (main & counter)
  • Rotate spindle (if possible), listen for abnormal noises
  • Check radial and axial play
  • Monitor heat, vibration
  • Check how the spindle is driven (direct, belt, gear)
• Turret / toolchanger(s)
  • Cycle the turret through all stations, check indexing repeatability
  • Check tool pocket wear, clearances, fit
  • If live tooling: check motor, rotation, runout, power under load
• Y-axis (if present)
  • Many TNK machines may have lateral offsets, check smooth travel and binding
  • Confirm alignment relative to main axes
• Back machining / sub-spindle (if equipped)
  • Check alignment, spindle coupling, mirrored functionality
• Coolant / lubrication / hydraulic / pneumatic systems
  • Inspect coolant tank, piping, pumps, filters, leaks
  • Lubrication pumps, oil lines, greasing systems
  • Hydraulic clamping units, pneumatics
• Covers, guards, panels
  • Are covers intact? Any missing panels? Wiring exposed?

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B. Electrical, Control & Electronics

• Power-up & control testing
  • Boot controller, observe error logs, alarm history
  • Jog all axes, test panel responsiveness
• Servo / drive / amplifier units
  • Inspect for heat damage, discoloration, smells, signs of repair
  • Check cables, connectors, shielding, strain relief
• Feedback devices / encoders / resolvers
  • Monitor signals during axis movement if possible
  • Ensure axes don’t lose counts or produce glitches
• Wiring / harness integrity
  • Check for brittle insulation, corrosion, loose or damaged plugs
• Memory / backup / parameter retention
  • Confirm that tuning parameters, offsets, G & M codes, macro programs are stored and retrievable
• Safety / interlock / limit circuits
  • Press E-stop, test interlocks, verify limits work properly

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C. Operational & Performance Tests

If allowed, run the machine under motion or even cutting:

1. Axis motion tests
   • Move X, Z (and Y if present) across full travel at various feed rates
   • Look for smoothness, jumps, binding, irregular motion
2. Backlash / reversal test
   • Move axis in one direction, then reverse, measure lost motion
3. Spindle rotation & vibration
   • Run main & counter spindles at multiple RPMs
   • Use a dial indicator or vibration sensor to check runout and vibration
4. Turret cycling
   • Cycle all turret tools, index, tool change times, repeatability
5. Test cutting / turning
   • Use a test bar or representative part
   • Perform turning operation; measure diameter, roundness, surface finish, tolerances
6. Live tooling test (if present)
   • Engage live tool, run at speed, check runout, power under load
7. Thermal stability
   • Let machine run for 30–60 minutes, monitor if axes drift, if temperatures stabilize
8. Chip / coolant handling
   • Operate coolant pump, chip conveyor, flushing systems under chip load

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3. Quantitative Assessment, Deviation & Metrics

After inspections and testing, make a quantitative assessment:

• Deviation from nominal specs
  • Compare your measured travels, speeds, spindle performance vs the published values
  • If X / Z travel is compromised or turrets have limited indexing, note that as reduction in capability
• Wear margin & residual life
  • Estimate how much life remains in guideways, screws, spindles
  • Particularly scrutinize turret and live tooling wear
• Error budgets
  • Backlash, lost motion, repeatability tolerances: how far off from what you need?
• Repair / refurbishment cost estimates
  • List items needing overhaul or replacement (spindles, drives, encoders, guideways)
  • Get price quotes for parts / labor
• Risk / downtime cost
  • Transport, reinstallation, alignment, calibration, downtime in your shop
• Upgrade / retrofit potential
  • If electronics are obsolete, how feasible is upgrading (modern control, drives)
  • Whether the machine has open architecture or is too proprietary

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4. Red Flags & Deal-Killers

Some problems may be severe enough to walk away:

• Cracks, warping, or heavy repairs to the main casting/frame
• Spindle(s) in poor shape, severely noisy, significant axial or radial play
• Turret indexing failure, excessive tool pocket wear
• Guideways or ball screws too badly worn to be economically repaired
• Feedback/encoder system failures with no spares or replacements available
• Control electronics so outdated or proprietary that parts are unobtainable
• Missing essential components (turrets, tooling, spindles, drives)
• Seller refusing motion / operational tests
• Environmental damage (flooding, corrosion, chemical exposure)
• Overlooked cost of transport, alignment, and re-certification

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5. Negotiation & Purchase Strategy

• Use your inspection data (defects, repairs needed) to structure price deductions
• Request a short “acceptance period” after installation (test on your parts)
• Ask for inclusion of spare parts, tooling, or warranty on critical items
• Compare total cost: purchase + transport + refurbish + downtime vs alternatives
• If possible, bring a specialist (e.g. someone experienced with Swiss / multi-axis machines)
• Insist on full disclosure of hours, faults, repair history