Here’s a field-tested, industrial perspective on how to spot quality (and risks) when evaluating a Pietro Carnaghi AC 20 TM CNC Vertical Lathe (vertical turret / boring / milling variant) as a used / surplus machine. Use this as a due-diligence checklist and decision framework. I’ll begin with reference specs, then walk you through inspection steps, red flags, and decision logic.

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Reference / benchmark specs & machine architecture

First, know what a good AC-series Carnaghi vertical lathe should be able to do. This gives you benchmarks against which to judge wear, deviation, or hidden damage. The following data is drawn from Carnaghi’s product lines and used listings.

Known / likely specifications (AC 20 TM / AC series)

• The Pietro Carnaghi AC series (single frame design) covers turning diameters from ~1600 mm to 3200 mm.
• For the AC20 (this being “20” in the model name), typical turning diameter ~ 2,000 mm (2 m)
• One used AC 20 TM 1800 listing gives: Max workpiece diameter 2,040 mm, turning height ~1,270 mm, ram stroke (Z) 1,250 mm, table speed range 1–320 rpm, table drive motor ~100 kW, drilling/milling spindle 37 kW, CNC Siemens 840 D, max workpiece weight 5,000 kg (per pallet/chuck)
• Another listing for AC20 TM gives faceplate Ø1,800 mm, swing ~2,000 mm, turning height ~1,270 / 1,120 mm, table speed up to 320 rpm, live spindle 3,000 rpm, etc.
• The Carnaghi architecture uses hy­drostatic guide supports (in many AC / vertical lathes) to provide high rigidity and reduced wear.
• Carnaghi highlights in its vertical-lathe product pages that in their AC design, the column is mounted to the table base; the crossrail is sized for severe cutting; guideways use hydrostatic pockets to reduce wear and vibration.

Thus a “healthy” used AC 20 TM should still approach these published ranges (or slightly below, depending on wear) in diameter, height, rotational speed, power, and consistency.

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What to inspect and test — detailed checklist & red flags

Below is a subsystem-by-subsystem checklist. Use it on-site: measure, listen, feel, stress-test where possible. Document deviations and note which subsystems carry more weight in your decision.

Subsystem / Feature	What to Check / Test	What a Healthy Machine Should Show	Possible Red Flags / Warning Signs
Structure / frame / castings	Inspect columns, base, crossbeam, saddle, welds, cracks, distortions	No visible structural cracks or repair welds, uniform surfaces, no obvious deformations	Weld repairs in high-stress zones, cracks near supports, sagging columns, misaligned parts
Column / vertical motion guides	Move ram up/down, reverse direction, listen and feel for binding, jerking, measure backlash	Smooth, consistent vertical travel, minimal backlash, no “dead zones”	Binding, jumps, friction zones, high backlash, uneven motion, jerky reversals
Crossrail / saddle horizontal motion (if applicable)	Command horizontal motion, check for smoothness, backlash, stiffness	Smooth traverse across full span, minimal backlash, consistent behavior	Binding at edges, sag in mid-span, uneven behavior, stiff zones
Table / spindle / faceplate rotation	Rotate table, check for bearing noise, vibration, runout with test bar	Quiet operation, minimal vibration, low runout within microns, stable rotation	Knocking or grinding in bearings, high vibration, wobble, large runout on test bar
Table drive / motor power	Run at various speeds (low to max), monitor current draw, stability, thermal drift	Stable operation across speed range, no abnormal current spikes or thermal drift	Motor overload, instability at high rpm, overheating, sluggish behavior
Ram / vertical spindle (if milling / drilling head)	Move head up/down, test spindle RPMs in milling mode, measure runout, check mechanical play	Clean motion, accurate RPM, minimal runout, no slop	Sloppy spindle motion, vibration at high rpm, high runout, inability to hold position
Tooling / turret / tool magazine	Cycle tool changes, check indexing, check stability under load	Precise, repeatable changes, stable toolholding, no collisions	Tool drop, mis-index, slop, collision marks, inconsistent cycles
Feed drives / servo / motors	Run feed axis, acceleration / deceleration, reversals, watch for drive faults	Responsive axes, no alarms, stable traction and motion	Drive trips, axis stalls, overshoot, jitter, inconsistent acceleration
Control electronics / cabinet / wiring	Inspect wiring, clean cabinets, check fans, look for burnt wires; power up, review logs, I/O, parameter stability	Neat wiring, no burned components, stable control behavior, no persistent alarms	Burn marks, broken wires, fan failures, error logs, corrupted parameters
Thermal stability / drift	Warm up machine, then re-measure reference geometry / positions to detect drift	After warm-up, positions stable, minimal drift over time	Significant drift in measurements over time, hysteresis in motion
Accuracy / repeatability tests	Use gauge blocks, test bar, multiple points, repeat cycles	Repeatability within tight tolerances (e.g. few microns), consistent across envelope	Inconsistent repeat measurements, drift across the travel, nonuniform accuracy
Load / machining test	If possible, mount a workpiece and run turning, boring, milling cycles; monitor performance	Stable cutting, clean finishes, no unexpected chatter, axes hold contour	Chatter, poor finishes, tool deflection, errors or alarms under load
Control features / special functions	Verify interpolation, probing, offsets, backup/restore, CNC functions	All functions operate correctly, no disabled modules, stable performance in advanced cycles	Missing license features, control errors under complex motion, program failures, parameter corruption
Documentation / parts / spares availability	Ask for manuals, wiring diagrams, parts lists, spare modules, refurbishment records	Complete documentation, known sources for critical spares, history of rebuilds	Missing manuals, undocumented modifications, nonstandard or obsolete parts, no traceable spare support

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Special cautions / things to watch for (vertical lathe / turret context)

Because vertical lathes (vertical turret / boring style) introduce unique stressors, here are additional cautions:

• Bearing condition in vertical orientation: The spindle / table bearings carry large radial and axial loads—look for wear signs, lubrication issues, thermal expansion.
• Gravity load & preload: Vertical motion systems often rely on preload or hydrostatic support; if preload is lost or hydrostatic systems degraded, you might see binding or variation downward vs upward travel.
• Hydrostatic guide systems: Many Carnaghi machines (including AC series) employ hydrostatic (oil film) guide supports to minimize wear and vibration. Degradation in hydrostatic systems (leaking oil, worn pockets, contamination) is a slow killer.
• Structural alignment under load: Because the workpiece is often heavy, the machining forces may flex the structure. It’s wise to test under near-full load conditions if possible.
• Spindle / ram rigidity under torque: When milling or drilling in the lathe, the head / spindle must resist bending and torque without losing accuracy.
• Consistency between axes: Because vertical turrets often combine turning & milling modes, misalignment between axes (X, Z, C) is more critical.

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How to interpret your findings & decision thresholds

After your inspections and tests, here’s how to decide whether a Pietro Carnaghi AC 20 TM is a viable purchase, demands heavy discount, or should be rejected.

1. Separate cosmetic wear vs functional defects
   • Surface rust, chipped paint, cosmetic damage are usually tolerable if mechanics are sound.
   • But defects in bearings, structural cracks, vertical guide damage, spindle vibration are serious.
2. Estimate repair / overhaul cost + risk buffer
   • For each defect, get or estimate parts, labor, alignment, calibration, downtime.
   • Your mark-down or discount must more than absorb these remediation costs.
3. Check spare parts & support for Carnaghi / vertical lathes
   • The value of such a machine heavily depends on availability of spindle bearings, guide systems, control modules, hydrostatic components, structural parts.
   • If parts are rare or expensive in Türkiye, build risk premium into your pricing.
4. Residual lifespan & maintenance burden
   • If the machine already exhibits extensive wear or repair history, anticipate major future rebuilds.
   • That should reduce your valuation accordingly.
5. Control / electronics obsolescence risk
   • Even a mechanically good machine is weaker if its CNC / control modules are obsolete or unsupported. Ensure control modules, parameter backups, firmware, and replacement electronics are available.
6. Negotiate acceptance / trial run period
   • Insist on a post-delivery acceptance window (e.g. 30–90 days) during which you can run real production parts and reject or demand fixes if performance is subpar.
7. Allow for reinstallation & alignment after transport
   • Moving such a machine often disturbs alignment, geometry, preload, etc. Always factor in time / cost for re-levelling, calibration, confirmation runs after installation.
8. Weighted scoring / pass/fail logic
   • Assign heavier weights to critical subsystems: spindle & bearing health, structural integrity, vertical guide performance, control electronics.
   • Even if many subsystems are “good,” failure in a high-weight item may justify rejection or steep discount.