1) Quick Snapshot — What “Good” Looks Like

• Geometry within spec after warm-up (flatness/straightness/squareness verified to ISO 230).
• Hydrostatic/box guideways hold pressure and temperature; no abnormal leakage, chatter, or stick-slip.
• Bridge & ram remain rigid at full Y/Z extension; no “head droop”.
• Spindle runs smooth (low vibration, healthy drawbar force), taper clean, tool retention consistent.
• Ballscrews/linear scales show minimal backlash; axis reversal is crisp.
• CNC control (commonly Siemens/Heidenhain) boots cleanly; no intermittent axis or PLC alarms.
• Way covers & bellows intact; lube and hydraulic systems stable (no contamination).
• Service history documented—especially guideway oil, hydraulic work, alignment/laser reports.
• Electrical cabinet clean/dry; fans and heat exchangers functional; no overheated terminals.

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2) Model-Specific Context (Why Portal Mills Are Different)

Portal (gantry) machines like the SL 240 MB are built for large, heavy parts with long travels and demanding surface quality. Key differentiators:

• Mass + span management: Accuracy depends on bridge rigidity and ram design under extension.
• Hydrostatic or heavily damped ways: Great finish/accuracy when healthy; expensive to repair if neglected.
• Foundation sensitivity: Level, thermal stability, and vibration isolation matter more than on small VMCs.

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3) Pre-Purchase Dossier — Ask the Seller for These

Category	Documents & Data You Should Obtain
Identity	OEM plate photo, serial number, year of build, original configuration sheet
Service	Full service logs, retrofit notes, laser/ballbar reports, geometry re-alignment records
Accuracy	Latest ISO 230-2/-6 tests (linear positioning, straightness, squareness, rotary if equipped)
Spindle	Hours, last rebuild date, max RPM & power, taper type, drawbar force test results
Motion	Ballscrew/guideway replacement history, scale model/firmware, backlash compensation tables
Fluids	Latest hydraulic oil report, guideway oil spec & consumption rate, coolant maintenance log
CNC	Control model/version, PLC/NC backups, postprocessors, option keys, probing & JOG/MDI demos
Safety	CE/UL compliance, emergency stop and door interlock tests, guarding status
Tooling	Included heads (angle/extension), toolholders, aggregates, right-angle heads, fixtures
Power	Installed kVA, peak current, transformer requirements, pneumatic demand
Logistics	Footprint & weight, disassembly plan, lifting points, transport drawings, foundation plan

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4) On-Site Inspection & Tests (Step-by-Step)

A. Visual & Static Checks

• Foundation & level: Verify leveling pads/anchor points; check for grout cracks or shim stacks.
• Bridge/ram: Inspect for collision marks, ram gib/guideway wear patterns, coolant ingress.
• Way covers/bellows: Look for tears, coolant/oil streaks on inner faces.
• Hydraulics/lube: No foaming, no burnt smell; accumulators charged; manifold leaks absent.
• Electrical cabinet: Check filters/fans, tight terminals, clean servo drives—photograph nameplates.
• Cable chains/hoses: Look for flat spots, kinks, brittle jackets; check minimum bend radius respect.

B. Power-On Functional

• Warm-up routine (30–60 min): Stabilize temps before measurements.
• Axis homing: Smooth, consistent; no abnormal following error spikes.
• Rapid & feed tests: Command 25/50/75/100% feed/rapid; listen for pitch changes or grind.
• Axis reversal: Small incremental jogs ±0.010–0.050 mm; feel for hesitation or overshoot.

C. Metrology & Motion Quality

• Laser interferometer (X/Y/Z): Check linear positioning error, backlash, repeatability; map vs OEM spec.
• Straightedge & autocollimator: Verify straightness of X (longitudinal) and Y (cross-rail/bridge) ways.
• Squareness (X↔Y, Y↔Z, X↔Z): Tram head; record deviation over full travel.
• Ballbar test (circularity): Run at center and corners of the envelope; compare warm vs cold.
• Ram droop: Indicate at spindle nose with ram retracted vs extended; quantify micro-radians or µm/1000 mm.
• Spindle health: Vibration spectrum (bearing bands), taper contact blue test, drawbar force with gauge.
• Surface finish trial: Face-mill test plate (e.g., 600×600 mm); inspect witness lines/waviness.

D. Thermal & Hydrostatic Systems

• Hydrostatic pressure & flow: Confirm against plate; monitor temp rise, look for pressure drift under motion.
• Lube consumption: Compare to spec; too low = starvation risk, too high = seal wear/leaks.
• Thermal growth study: Run a 2–3 hr production-speed cycle; measure drift on a reference artifact.

E. CNC & Automation

• Alarms & diagnostics: Review history; check axis load graphs at common feeds/cuts.
• Scales/encoders: Confirm closed-loop status, reference marks, error compensation tables.
• Probing: If fitted, calibrate spindle/tool probe; verify repeatability on gauge sphere.
• Options: High-speed machining, look-ahead, probing cycles, 5-face/5-axis heads—confirm licenses.

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5) Wear & Failure Patterns to Watch

• Bridge way wear near travel extremes → straightness errors, pattern in surface finish.
• Ram headstock play → taper wear, chatter under side-load cuts.
• Hydrostatic leaks at manifold/seals → pressure instability, poor finish.
• Backlash creep in X or Y → ballscrew/ballnut wear or loose thrust bearings.
• Scale contamination → intermittent position jumps; seals and air purge lines compromised.
• Drawbar fatigue → low retention force, pull-stud fretting.
• Way cover ingress → grinding paste effect on ways and screws.

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6) Acceptance Criteria (Practical Targets)

• Linear positioning: ≤ ±(5–10) µm/m (confirm against the machine’s original spec).
• Bidirectional repeatability: ≤ ±(2–3) µm.
• Straightness: ≤ 8–12 µm/m in X and Y; Z ram ≤ 10–15 µm/m.
• Squareness: ≤ 0.02–0.04 mm over full span (tighten if your parts demand it).
• Circularity (ballbar, 100–300 mm dia): ≤ 15–25 µm.
• Spindle runout at gauge: ≤ 2–5 µm; drawbar force within OEM nominal (often >70% of new).

(Tighten these if you machine molds/dies or aero-structures; relax slightly for roughing work.)

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7) Tooling, Heads & Workholding (High-Value Inclusions)

• Right-angle/extension heads with recent rebuilds and tight cones.
• Calibration kit: ballbar, Renishaw probe tips, master sphere, squares, granite parallels.
• Large vises/fixtures and modular plates; rotary/turning tables if the MB was configured for them.
• Coolant/through-spindle hardware, filtration, mist collection, and chip conveyors sized for long swarf.

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8) Infrastructure & Installation Checklist

• Foundation: Confirm OEM plan; check soil bearing, rebar, and isolation from nearby presses/hammers.
• Power: kVA, voltage, transformer taps; surge protection; clean earth.
• Air: Dry, oil-free; pressure/flow per spec; dedicated line for tool change/air purge.
• Coolant management: Sump volume, tramp-oil skimmer, filtration (bag/paper), disposal plan.
• Rigging plan: Disassembly order, bridge locking, ram support, lifting eyes, transport height/width limits.
• Re-commissioning: Leveling, laser checks, backlash comp update, ballbar, and cut part validation.

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9) Pricing & Value Drivers

• Premium signals: Recent geometry correction with reports, spindle rebuild, new scales/cables, fresh way covers, documented hydrostatic work, and modern CNC retrofit.
• Discount signals: Missing test reports, high guideway oil usage, persistent thermal drift, drawbar below spec, oil leaks, or foundation uncertainty.
• CapEx foresight: Budget for transport + installation + laser/ballbar + possible spindle/ram refresh (often 8–15% of purchase price for large gantries).

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10) Red-Flag Alarms (Walk Away If…)

• Non-recoverable geometry (twist in bed/rails) beyond compensation range.
• Hydrostatic system cannot hold pressure/temperature under load.
• Repeated axis following-error or scale faults after basic maintenance.
• Structural crash history (ram/bridge) with unresolved alignment variance.

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11) Sample On-Site Test Program (You Can Hand to the Technician)

1. Warm-up 45 min with OEM cycle.
2. Laser X/Y/Z (bidirectional), apply comp only if within OEM limits.
3. Ballbar center and near each corner at two feedrates.
4. Ram droop and Z straightness with and without head extension.
5. Spindle: vibration FFT, thermal rise (30 min @ 70% RPM), drawbar force test.
6. Cut test: Face-mill plate (aluminum/steel per your work); record Ra and step.
7. Thermal drift: 2-hr duty run; re-measure a reference feature every 20 min.
8. Hydrostatic: log pressure/flow/temp idle vs feed; inspect return filters.
9. CNC/PLC: alarm history download, backups, option/license verification.

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12) Buyer’s Pocket Checklist (Print & Take)

• Serial plate photos; OEM build sheet; service & geometry records
• ISO 230 laser/ballbar data within your tolerances
• Hydrostatic pressure/flow stable; no unusual leaks
• Ram/bridge rigidity acceptable at full extension
• Spindle drawbar force & runout within spec
• Scales/encoders clean; compensation tables reasonable
• Way covers/bellows intact; lube and hydraulics clean
• Electrical cabinet clean; fans & exchangers working
• Tooling/heads included and inspected
• Foundation plan and re-commissioning budget confirmed

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Pro Tip (for Negotiation)

Request the seller to re-run the acceptance tests after relocation at your site with an agreed tolerance window. Hold back a portion of payment until the machine meets the agreed post-install results.