Here’s a professional guide in English for evaluating a pre-owned / second-hand Kellenberger KEL VARIA RS 175/1000 CNC Cylindrical OD Grinder. This checklist will help you avoid costly mistakes and hidden repair expenses.

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I. Typical Specs / Reference Values

Before inspection, know the expected specs so you can challenge seller claims:

Feature	Typical Values (RS 175/1000)
Distance between centers	~ 1,000 mm
Center height	175 mm
X-axis travel (wheelhead)	~ 320 mm
Z-axis travel (longitudinal)	~ 1,150 mm
Grinding wheel size	Ø 400 × 50 mm (right wheel)
Wheelhead swiveling range	–210° to +30°
Workhead speed	8 – 8,000 rpm
Control system	Typically Heidenhain CNC

These are standard reference points. If the seller claims unrealistic numbers (e.g., 12,000 rpm workhead, 1,500 mm centers), demand proof.

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II. Documentation & Provenance

Always request:

• Service and maintenance logs (spindle overhauls, bearing replacements, alignments).
• CNC control backups (parameters, macros, programs).
• Electrical, hydraulic, pneumatic schematics.
• Modification/retrofit records (control upgrades, drive replacements).
• Usage history (operating hours, materials processed, duty cycle).
• Accessories and spare parts included in the sale (chucks, steady rests, coolant units, tooling).

Weak or missing documentation = high risk.

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III. Visual / Structural Inspection (Before Power-Up)

Check the machine’s condition without applying power:

• Castings / frame: Look for cracks, welded repairs, distortions.
• Guideways and slides: Check for scoring, pitting, rust.
• Covers, wipers, bellows: Missing or damaged covers allow chips/coolant to invade.
• Wheelhead, spindles, housings: Signs of oil/coolant leaks.
• Electrical cabinet: Check for corrosion, water damage, burnt boards.
• Coolant/filtration system: Leaks, rust, clogged filters.
• Overall cleanliness: Poor external condition often signals poor internal care.

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IV. Motion / Mechanical Tests (With Power, No Cutting)

If the seller allows power-up, run these tests:

1. Control boot: Look for alarms, missing modules, error logs.
2. Axis jogging: Move X and Z axes through full travel at slow/medium speed.
   • Check for binding, jerky motion, dead spots.
   • Reverse direction to measure backlash with an indicator.
3. Wheelhead swivel: Test full range; confirm smooth motion.
4. Servo drives: Listen for abnormal whine, vibration, lag.
5. Auxiliary systems: Run coolant pumps, lubrication, hydraulics; check flow, leaks, consistency.

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V. Spindle & Wheelhead Tests

Critical for grinding accuracy:

• Spindle run (no load): Run through full speed range; listen for bearing hum, vibration.
• Runout test: Use a test bar to measure radial and axial runout over 360°.
• Wheel mounting faces: Inspect for scoring, burrs, or wear.
• Wheelhead swivel: Check for sag or misalignment at extreme angles.
• Balancing: Ensure wheels run smoothly without excessive vibration.

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VI. Test Grinding / Accuracy Verification

This is the real proof of performance:

• Mount a reference bar or part. Check straightness, taper, roundness.
• Test repeatability: retract/return to the same position and measure deviation.
• Perform a light finishing grind; measure surface finish, dimensional accuracy, cylindricity.
• Test near axis travel limits (start, mid, end).
• Run machine for 20–30 minutes, then re-check dimensions to identify thermal drift.

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VII. Common Wear Points / Hidden Costs

Be prepared for:

• Worn wheelhead or workhead bearings.
• Axis screw/nut backlash, guideway wear (may require re-scraping).
• Servo drives or motors nearing end of life.
• Obsolete control modules or electronics.
• Aging cabling, connectors, insulation failures.
• Coolant system pump/filter overhauls.
• Costly re-alignment or reconditioning after installation.

Budget 10–20% of the machine price as a refurbishment reserve.

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VIII. Negotiation & Deal Safeguards

Protect yourself by structuring the deal:

• Require an acceptance test period (motion, spindle, grinding accuracy).
• Hold back part of payment until performance is proven.
• Demand all documentation and backups.
• Ask for a written condition disclosure from the seller.
• Negotiate a short warranty (30–90 days) on spindle, drives, wheelhead.
• Define responsibility for transport, installation, leveling.
• Request inclusion of tooling, wheels, accessories, spare parts.

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IX. Red Flags (Walk Away If You See These)

• Seller refuses test cuts or motion tests.
• Excessive backlash, jerky axis motion.
• Spindle vibration, noise, or high runout.
• Wheelhead sag, poor swivel accuracy.
• Turret/fixture misalignment (if applicable).
• Burnt or corroded electronics.
• Cracked castings or welded repairs.
• Missing covers/guards.
• Spare parts unobtainable.