Below is an industrial-grade checklist + insight guide for assessing a pre-owned / surplus FANUC Robodrill D21MiB5 (vertical machining center / drill-tap machine) to help you decide whether it’s a solid buy. (You might see variants “D21MiB5 Plus / ADV / 24K” etc.; use the specs of the specific variant as your benchmark.)

First I summarize key specs (so you know what “should” be good), then walk through subsystem inspections, red flags, and decision logic.

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Key reference specs & benchmarks

Before going on site, arm yourself with the nominal specs of the Robodrill D21MiB5 so you can spot deviations. The following come from FANUC datasheets:

• Travels (X / Y / Z): 500 × 400 × 330 mm
• Table size: 650 × 400 mm
• Max table load: 300 kg
• Spindle options: 10,000 rpm standard, with optional 24,000 rpm high-speed variant
• Spindle power / torque (10,000 rpm, 1 min): ~ 14.2 kW / 80 Nm; continuous: ~ 4.0 kW / 13.6 Nm
• Rapid traverse (X, Y, Z): 54 m/min
• Maximum programmable cutting feed: 30,000 mm/min
• Tool change time (2 kg tool, cut-to-cut): ~ 1.6 sec
• Bidirectional accuracy: < 0.006 mm
• Bidirectional repeatability: < 0.004 mm
• Control: FANUC 31i-B5 Plus (or equivalent)

These are the standards you should try to see the machine approach (or not deviate excessively).

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Key inspection & test checklist (by subsystem)

Use this on site — take measurements, listen, feel, stress-test where possible:

Subsystem / Feature	What to Inspect / Test	What “Good / Acceptable” Looks Like	Red Flags / Warning Signs
Frame, base, column structure	Visual inspection of castings, frame, support welds, any repaired cracks	No structural cracks, no suspicious weld repairs, uniform surfaces, no twisting	Weld patches in high-load zones, cracks near column base or bed, misalignment visible
Way covers, bellows, guards	Move axes slowly, observe covers and bellows for dragging, interference, torn sections	Covers move freely, no binding or contact with axes or table	Torn bellows, sagging covers, covers contacting table or supports
Linear guides / ball screws / backlash	Jog each axis, reverse direction, measure backlash with a dial indicator, test for “dead” zones	Backlash small (within a few microns), smooth motion, uniform response across travel	Excessive backlash, binding in certain zones, roughness or vibration in slow motion
Spindle (milling / drill mode)	Run spindle across speed range (low → high), listen for bearing noise, measure runout (test bar), monitor temp rise	Quiet at all speeds, vibration low, runout in microns, stable temp over time	Humming / knocking sounds, high vibration, thermal drift, wobble in test bar
Tool changer / magazine	Cycle all tool changes, test indexing, tool pick/drop, measure time, check for mis-index	Fast, repeatable tool changes without error, secure tool holding	Tool drop, mis-indexing, worn pockets, slow or inconsistent indexing, collision marks
Servo drives / axis motors / electronics	Rapid traverse, accelerations, decelerations, reversals; watch for faults, current spikes or instability	Responsive axes, no servo faults or alarms, stable behavior under all motions	Fault alarms, drive trips, axis stiffness or oscillation, overheating amplifiers
CNC control / wiring / cabinet	Open the control cabinet, inspect wiring, check for burnt connectors or discoloration, test fans; power on, check for error history, I/O signals, parameter memory	Clean wiring, no burnt parts, fans operational, control boots clean, parameter memory healthy, no persistent alarms	Burn marks, broken wires, fan failure, parameter corruption, erratic behavior
Thermal stability / warm-up drift	Run machine for a period, then re-check reference positions or test cuts to see drift	After warm-up, machine stabilizes; minimal drift in positions	Positional drift over hours, offsets changing with temperature, hysteresis
Accuracy / repeatability	Use gauge blocks, test bars, measure multiple points repeatedly	Repeatability within small tolerance (e.g. < 0.005 mm or better), consistency over range	Variation in repeat position, larger error than spec, variation across table travel
Load / cutting test	If allowed, run a representative part or contour under typical cutting / tapping loads	Stable performance, no chatter, good surface finish, axes hold contour, no alarms	Chatter, tool deflection, axis stalls, poor finish, servo errors, inconsistent performance under load
Tapping / drilling cycles	Run tapping/drilling routines, including rigid tapping, speed reversals, tapping under spindle load	Tap cycles clean, minimal vibration, accurate threads, no slippage	Thread errors, chatter, missed taps, slippage in tapping mode, problems reversing direction
Software / CNC features / options	Check that all control options (probes, offsets, macro functions, interpolation) are active and functioning	All licensed options working, parameters accessible, control stable with advanced features	Missing option licenses, control crashes under advanced routines, parameter memory issues
Documentation / spare parts	Request manuals, wiring diagrams, parts list, software backups	Complete documentation, parts lists, known suppliers, history of servicing	Missing manuals, no parts catalog, unknown modules, control firmware not backed up

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Red-flag “deal breakers” you should not ignore

When inspecting, these issues are especially dangerous / costly, and may justify walking away unless price is extremely low:

1. Spindle bearing noise / excessive runout under test bar — indicates imminent failure.
2. Irreparable backlash in axes — if ball screws or guide systems are worn beyond adjustment.
3. Servo drive faults / instability / frequent alarms — control electronics are often expensive to replace.
4. Control cabinet / wiring damage (burned wires, melted insulation) — suggests past short circuits or electrical trauma.
5. Thermal drift too high / unstable geometry — hard to compensate in production use.
6. Tapping / drill mode failures — since D21MiB5 is used for drilling / tapping, this is core functionality.
7. Missing or corrupt control software / parameter memory — if CNC cannot load parameters, you may lose ability to restore functioning state.
8. No documentation / missing parts lists / missing maintenance history — increases risk of hidden issues.
9. Unavailability of spare parts for FANUC Robodrill / specific modules in your region — leads to long downtimes or high cost.

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Decision logic & offer negotiation framework

Once you’ve collected observations and measurements, here’s how to interpret and decide:

• Qualify “acceptable deviation”: Some wear is expected in a used machine. Create tolerance thresholds (e.g. < 10x spec in backlash, < 20% deviation in spindle runout) beyond which you reduce your valuation.
• Repair / risk margin estimation: For each defect you find, estimate parts cost, labor, downtime, and margin. Subtract that from the “as-equivalent new / good used” value and negotiate accordingly.
• Spare parts & service support check: Ensure you can source replacements (spindle bearings, servo drives, control modules, tool changer parts) locally or affordably. If not, the machine’s value drops materially.
• Residual useful life: Derive how much life remains based on wear signs. Use that to discount the machine.
• Control / software risk: Even a mechanically good machine may be hampered by outdated or unsupported control electronics; ensure replaceability or upgrades.
• Acceptance / validation window: Try to negotiate a post-delivery acceptance / trial window (30–90 days) under production conditions where the seller must remedy hidden defects or you can reject.
• Transport / re-installation risk buffer: Always assume that reinstallation, realignment, calibration will be required after moving the machine. Factor in time & cost for final tests.
• Weighted scoring: Assign more weight to critical subsystems (spindle, axes, drive electronics, tapping function) over less critical subsystems. If a high-weight category fails, that may be sufficient to reject or demand a large discount.