Here’s a Smart Buyer’s Guide tailored for evaluating a pre-owned / used / surplus Ernault Somua Cholet 550 Universal / Center Lathe (or similar heavy conventional / semi-automatic lathe). Because this is a “universal / heavy” lathe (not a CNC multitasker), the checklist emphasizes mechanical integrity, wear, alignment, and any added automation.

First I list known spec ranges for the Cholet 550 so you know what “normal” is, then a detailed inspection & evaluation checklist, key risk zones, acceptance criteria, pricing/valuation strategy, negotiation tips, and what to do after purchase.

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1. Baseline / Reference Specifications of Cholet 550 (What “Good” Should Be)

Before visiting a candidate, you should have reference benchmarks. Below are specs collected from used-machine listings and datasheets to guide your expectations. These can vary by version / year / accessory, so treat them as ballpark zones, not absolutes.

Specification	Typical Value / Range	Notes / Source
Center height / point height	~ 250 mm	“Centre height: 250 mm” in datasheet.
Max swing over bed	~ 500 mm – 550 mm	Many adverts list “Ø over bed 500 mm”
Max swing over cross slide / carriage	~ 310 – 312 mm	A listing gives “Ø over cross slide 310 mm” l
Spindle bore / through hole	~ 52 mm	Multiple ads list “spindle bore 52 mm”
Distance between centers	variable — e.g. 1,000 mm to 1,800 mm	One data sheet: 1,000 mm between centers other ads 1,600 mm
Spindle speed range	32 – 1,600 rpm (and a low range variant)	E.g. 32 to 1600 / 16 to 800 speeds (18 speeds)
Power / Motor requirement	~ 7.4 kW (or ~8.5 kW in some)	One listing: “spindle motor power 7.45712 kW” another “Power: 8.5 kW”
Bed width	~ 384 mm	One listing “bed width 384 mm” under “Cholet 550 KH4”
Travel of cross / longitudinal slides	(advertised in some listings)	E.g. one datasheet gives “travel Y (support) 350 mm etc.”
Tailstock quill travel	~ 120 mm	In datasheet: “tailstock quill adjustment: 120 mm”

These numbers give you a target to compare what the specific machine offers / has degraded to.

Also note that older lathes were often retrofitted with DROs (digital readouts), threading gearboxes, steady rests, gap-beds, power feeds, etc., so expect variation.

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2. Inspection / Evaluation Checklist (What to Check On-Site)

Here’s a detailed checklist. Bring measurement gauges, straight edges, dial-test indicators, micrometers, your own test parts, and possibly a trusted machinist. Mark each item as OK / borderline / fail.

Subsystem / Area	What to Inspect / Test	Acceptable Condition / Red Flags
Documentation & History	Manuals (gear charts, lubrication, parts exploded views), maintenance logs, repair history, retrofits / upgrades, schematic diagrams	Full documentation is a plus. No documentation is a risk (you may not know past repairs).
Frame, Bed & Structure	Visual inspection for cracks, weld repairs, distortions, warped bed, bent surfaces, cracked base or support	Any structural repairs or warping are red flags. The bed must be rigid and straight.
Bed Ways / Guideways	Use a long straightedge / level / surface plate / test indicator to check flatness and wear across the bed; feel for dips / wear zones; use a stiff gauge to check sag	Acceptable wear only within your tolerance. Deep grooves, depressions, or flattening are major problems
Cross Slide / Carriage / Tool Slide	Move carriage across full travel, feel for binding or tight zones, test backlash, consistency, smoothness; inspect dove-tail slides for scoring or edge wear	Smooth motion without significant “hard spots” or binding. Excessive play or scoring is a problem
Feed / Nut / Lead Screw & Gear Train	Inspect all screws and nuts for backlash or play; check gear mesh, alignment, lubrication; test rapid traverse (if functional)	Backlash should be minimal. Worn nuts / screws or misaligned gears are serious.
Spindle & Bearings	Rotate spindle by hand (no load) and with moderate load (if possible); test for noise, stiffness; measure run-out of spindle bore using test bar; check bearing backlash	Minimal noise, smooth motion. Run-out within acceptable tolerance. Bearing slop or noise is a red flag.
Spindle Drive / Motor / Gearbox	Inspect drive motor, belts / couplings / gearbox (if any), examine alignment, vibration, heating	Drive system should run clean, no unusual vibration, minimal heating, no misalignment
Chuck / Workholding	Inspect chuck and jaws: run-out when mounted, grip consistency, jaw condition; check chuck mount, run-out on face; inspect tailstock alignment & quill	Chuck run-out should be low; jaws should grip consistently. Worn or damaged jaws reduce precision
Tailstock & Center	Move tailstock quill through travel; inspect alignment of tailstock to bed / spindle; check for play; test locking mechanism	Tailstock must align properly; no excessive play in quill or looseness in locking
Gearbox / Threading / Change Gears	If the lathe has threading or change-gear attachments, test all feed rates and thread functions; inspect gear teeth, backlash, noise	All feeds and thread pitches should engage smoothly without harshness or binding
Power Feed / Lead / Cross Feed Mechanisms	If equipped, test power feeds (longitudinal / cross) across full range; check smoothness, consistency, and vibration	Feeds should be smooth and stable. Any jerky or erratic feed is suspicious
DRO / Readout / Instrumentation (if present)	Verify that digital readouts / position indicators (if fitted) are functioning and accurate by checking motion vs actual movement	If DROs are inaccurate or nonfunctional, you lose a key advantage
Cooling / Lubrication / Chip Removal	Inspect coolant pump, piping, nozzles, sump; lubrication oil lines to slides and gearbox; chips / chip pan; cleanliness; check for leaks	Cooling and lubrication must work reliably. Leaks, blockages, or contamination are warning signs
Electrical / Control (if has power feeds, possibly CNC addons)	Inspect wiring, switchgear, motors, control boxes, fuses; check how power feed controls / switches operate and wiring integrity	Wiring should be clean and original. Burnt wires, splices, or corrosion are risks
Run / Test Operation	Run a test cut or turning operation with representative material; check surface finish, cutoff behavior, concentricity, part accuracy	The machine must produce parts within your tolerance. Poor finish, chatter, or inaccuracy is critical
Thermal Stability / Long-Run Test	Run the lathe for an extended period and monitor any drift in alignment, temperatures of bearings or drives, loosening of bolts	If geometry drifts over time, internal problems or lack of stability exist
Spare Parts / Accessories	Ask what accessories, chucks, steady rests, toolposts, backup parts, spare bearings the seller will include	A good set of accessories and spare parts adds much value
Acceptance / Trial	Request a short acceptance or test period (e.g. you test with your parts after delivery)	Always beneficial. If seller refuses, risk is higher

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3. Key Risk Areas & “Hidden Trouble Spots” for Heavy Universal Lathes

Because these machines are older, heavy, and often abused over time, some failure modes are common:

• Bed wear / sag / twist — repeated use can cause wear zones or bending in the bed.
• Slide / carriage wear — dove-tail slides are vulnerable to scoring or edge chipping.
• Worn lead screws / nuts, backlash — especially after many hours of use.
• Spindle bearing degradation — e.g. looseness, noise, overheating, especially under load.
• Misalignment between headstock and tailstock — after transport or abuse, alignment may shift.
• Geartrain wear, backlash in gears / change gears — may slip under load.
• Chuck / jaw wear — jaws lose grip accuracy over time.
• Cooling / lubrication neglect — old, dirty coolant or lack of lubrication accelerates wear of guides and gears.
• Electrical / motor / wiring aging — wires may have degraded insulation, bad connectors, or prior splicing.
• Hidden past repairs / welds — structural welds or repairs to bed, cross slide, or carriage might indicate past damage.
• Lack of maintenance / neglect — many old machines have missing grease lines, clogged passages, or forgotten repairs.
• Control / power feed failure — older electrics may be nonfunctional or difficult to repair.

These are the weak points to scrutinize heavily.

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4. Acceptance Criteria & Thresholds

Before inspection, define your “go / no-go” tolerances, based on what your parts demand. Examples:

• Spindle bore run-out: ≤ X micrometers
• Carriage / slide backlash: ≤ Y micrometers
• Bed straightness / flatness deviation: within your tolerance over test length
• Part turning accuracy: within your spec in test pieces
• Chuck run-out: acceptable for your parts
• Feeds / threading function all correct
• Motor / drive operation smooth under load
• Thermal drift limited over e.g. 1 hour test
• Cooling / lubrication systems operational
• Structural and mechanical integrity — no critical defects
• Electrical systems safe and functional
• Spare parts / accessories included
• Documented defects and repair allowances

If any critical threshold is violated, either negotiate strongly or reject.

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5. Valuation & Pricing Strategy

When evaluating asking price:

• Use comparable market prices of Cholet 550 lathes in similar condition (look at listings).
• Subtract estimated cost of repairs, alignment, refurbishment, parts replacement, shipping and installation.
• Add value for any included accessories (steady rests, chucks, faceplates, toolposts, spare parts).
• Include your risk premium (unknown defects) in your offer.
• Consider cost of downtime during commissioning / set-up.
• Verify that spare bearings, nuts, gear parts etc. are still available.
• If machine includes DRO or power feeds or upgrades, that can add value.
• If the seller is insisting “as-is, no return,” demand a deeper discount.

Your initial offer should leave margin for discovered defects.

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6. Negotiation & Risk Mitigation Tactics

• Live test & demonstration: Bring a test piece or sample and ask seller to let you run cuts.
• Cold inspection: Inspect inside mechanicals and wiring when machine is powered off.
• Document defects & photos: Use your checklist, take photos, and share them with seller as negotiation leverage.
• Get test run videos / data: Ask for videos under load, measurements, etc.
• Conditional acceptance / return window: Try to arrange that you can reject or renegotiate after delivery test.
• Require spares / accessories: Insist that chucks, tails, toolposts, spare bearings or parts are included.
• Share transport risk: Make sure contractual responsibility for damage remains with seller until acceptance.
• Request baseline alignment or measurement data: So you can verify after delivery.
• Walk-away clauses: Be ready to decline purchase if critical issues appear onsite.

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7. Post-Installation Checks & Commissioning

After you install the machine:

1. Careful leveling, alignment, and skirting — ensure bed is level, headstock and tailstock aligned.
2. Baseline measurement — use test bars, indicators, measuring tools to capture run-out, straightness, backlash, etc.
3. Test parts / trial runs — run your actual parts and measure outputs.
4. Thermal / long-run tests — let machine run for extended period and check drift.
5. Lubrication and coolant validation — ensure all grease / oil / coolant lines working.
6. Instrument checks / calibration — if DROs or scales are installed, calibrate them.
7. Maintenance plan — schedule periodic checks, cleaning, adjusting, checking alignment.
8. Spare parts stock — arrange critical spares (bearings, nuts, gears).
9. Performance tracking — periodically re-measure test parts and compare to baseline to detect wear early.

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8. Summary & Final Advice

• The Ernault Somua Cholet 550 is a robust conventional / universal lathe. Knowing its approximate specs (250 mm center height, ~500 mm swing over bed, spindle bore ~52 mm, speeds up to ~1,600 rpm) helps you judge manufacturer claims.
• A used Cholet 550’s key value lies in the structural integrity of the bed / ways, spindle and bearings, slide / carriage wear, and the geartrain / feeds system.
• Use a systematic checklist focusing heavily on mechanical wear, alignment, drive systems, and test cuts.
• Define your acceptance thresholds in advance; don’t allow vague promises.
• Negotiate using documented defects; insist on spare parts, a test period, and transport-risk clauses.
• After installation, be rigorous in alignment, baseline measurement, test runs, and preventive maintenance.