08/10/2025 By CNCBUL UK EDITOR Off

Technical Evaluation Guide: How to Identify a Quality Used, Secondhand, Pre-Owned, Surplus Campbell 930 CBN 5 Axis CNC Form/ Creep-Feed Grinder made in USA

1) Machine Overview & Typical Specs

Before visiting the machine, familiarize yourself with published specs so you know what “good” means. The Campbell 930 series is a vertical 5-axis (X, Y, Z, B tilt, C rotary) creep-feed / form grinder.

Key features typically include:

5-axis simultaneous contouring control (Fanuc 31i or equivalent)
Linear glass scales or direct feedback on all axes
Rigid frame, box structure, traveling-column style
High-power grinding spindle (30–60 HP, or up to 100 HP in some versions)
Very tight accuracy tolerances: ~5 µm in X, Y, Z axes; B & C angular accuracy in arc-seconds
Optional features: disk or roll form dressers, wheel balancing, tool probing, milling/drilling capabilities, gap eliminator, etc.

Example: a listing of a 930V-30/24/24 (30 HP) model is offered with auto tool changer, reconditioned spindle, GE Fanuc 15-M control, etc.

Use the seller’s spec sheet to pin down your target tolerances, travel ranges, power ratings, and features before you inspect.

2) Pre-Inspection Document Checklist

Ask the seller to provide in advance:

Full machine specification / build sheet (model version, spindle HP, options)
Serial number and build year
Control version and software level
Maintenance / service logs (spindle rebuild, axis servicing, lubrication)
Calibration & geometry / test reports (if available)
List of past crashes, collisions, or repairs
Spare parts list (dresses, spindle parts, sensors)
Electrical, hydraulic, pneumatic schematics
CNC parameter backup, compensation tables, calibration offsets

Having those allows you to evaluate how far out of spec the machine may be and what repair risk exists.

3) Static & Visual Inspection (Machine Power Off)

Walk around and inspect:

Frame and base for cracks, weld repairs, corrosion, signs of overload or collisions.
Column, bridge, and traveling-column structure for alignment issues, deflection, or twist.
Way covers, bellows, guards for damage, missing parts, chip intrusion.
Table, rotary table / C-axis, pallets: flatness, wear, mounting surfaces.
Tilt (B-axis) and rotary (C-axis) bearing housings: check casing for cracks or deformation.
Spindle nose and taper: check for rust, scoring, damage to taper surfaces.
Dressers (disk or roll): inspect condition (faces, wear, mounting).
Tool changer, tool magazine, grippers—look for wear, slop, misalignment.
Cable chains, hoses, coolant lines, pneumatic/hydraulic lines — check for damage, brittleness, previous repairs.
Electrical cabinet: open and inspect wiring, relays, cleanliness, signs of overheating, dust, rodent damage.
Safety guards, interlocks, doors, enclosures: verify integrity and function.

4) Installation / Alignment & Mounting Checks

If possible to temporarily mount or interface:

Check machine level and base mounting — uneven bases lead to geometry errors.
Use a test bar or indicator to measure runout / alignment at neutral B/C position.
Command small jogs in X/Y/Z and confirm readback corresponds (if scales or encoders).
Tilt / B-axis mechanical test: command small tilt motion and observe movement smoothness, binding, or backlash.
Rotary (C-axis) test: rotate under minimal load and observe encoder readback, smoothness, and load consistency.

5) Power-On & Dynamic Tests

With machine powered and safety protocols in place:

Warm-up: Jog axes continuously for 20–30 min to stabilize temperature.
Home / zero return: Check repeatability of reference position.
Axis motion: Move X, Y, Z at various speeds (25 %, 50 %, 100 %) — listen for chatter, binding, or noise.
Tilt / B-axis, rotary / C-axis: command motion while machine is idle and ensure smooth, error-free rotation.
Spindle ramp: Gradually ramp up spindle rpm, monitor vibration, noise, temperature changes.
Grinding spindle test: Run the spindle under light load (if safe) and verify stable current draw.
Tool change cycles: Run tool change sequences, test reliability of magazine, gripper, tool pick/place.
Dressing cycles: Activate dresser (disk/roll) to verify operation, repeatability, and no binding.
Coolant / lubrication systems: Turn on coolant, monitor flow, pressure, check for leaks, verify lube to axes.
Controls & alarms: Monitor for servo faults, axis overcurrent, limit switch trips; review alarm history.
Feedback & scales: If direct glass scales or feedback systems present, move and confirm no dropouts or errors.

6) Accuracy, Repeatability & Metrology Tests

These are critical for form/grinding performance:

Linear positioning accuracy: Use laser interferometer or calibrated displacement measuring system to check X, Y, Z axes (ideally within ~5 µm or as per spec).
Backlash / reversal error: Jog small increments (±0.01 mm) and measure difference on reversal.
Repeatability: Execute multiple cycles (e.g. 10×) of same move and measure deviation.
Squareness / orthogonality: Test X–Y, Y–Z, X–Z via precision squares or laser collimation.
Angular index accuracy (B, C axes): Index B and C to nominal positions multiple times, measure deviation in angular position (arc seconds).
Combined interpolation test: Command complex 5-axis contour moves (tilt + rotate + move) and measure the result vs intended path.
Thermal drift: Run under load for extended time (1–2 hr), re-check reference features to see shift.
Hysteresis / drift in tilt / rotary: Tilt to angle, hold, then return to zero and measure offset.

7) Spindle, Abrasive System, Dressers & Tooling Checks

Spindle runout: Use a high-precision test bar to measure radial & axial runout at the spindle nose.
Spindle noise & vibration: Use an accelerometer or vibration analyzer to detect bearing defects.
Spindle temperature rise: Run at moderate rpm for 30 min, measure temperature increase.
Spindle load behavior: Under light grinding load, current should remain stable, not spike.
Abrasive / CBN wheel interface: Check wheel mount, locking mechanism, wheel surface condition.
Wheel balancing: If machine has balancing, test balance function.
Dresser operation: Engage dresser, check path, repeatability, no binding, no excessive play.
Tool / nozzle changer (if fitted): Test change cycles, verify alignment and repeatability.

8) Lubrication, Cooling, Filtration & Auxiliary Systems

Cooling system: Check pump flow, pressure, clarity of coolant/abrasive fluid, leak points.
Filtration / recirculation: Inspect filters, screens, lumps or abrasive dust accumulation.
Lubrication system: Confirm oil / grease supply to all axes, check for blocked lines, leaks, or oil contamination.
Chip / abrasive handling: Check chip conveyors, waste removal, dust / slurry management.
Hydraulic / pneumatic systems (if present): Inspect pressure, valve behavior, leaks, stability.
Enclosure, fume / mist extraction: Check that the machine’s guarding, mist / dust collectors, coolant splash protection are intact.

9) Wear Patterns & Risk Areas to Watch For

Axis guideway wear: dents, scoring, backlash creeping.
Tilt / B-axis bearing wear: loose swivel, increased angular error.
C-axis rotary drift or slop: encoder errors under load.
Spindle bearing wear: increased noise or vibration even at low rpm.
Dresser head wear or play: inaccurate dressing cycles.
Coolant / abrasive slurry corrosion: damage to ways, covers, seals.
Contaminated lubrication: abrasive ingress to bearings, wear.
Electrical / control aging: failing capacitors, outdated drives, repeated faults in alarm log.
Cable fatigue or chain damage: broken wires or intermittent sensor signals.

10) Documentation & Records to Collect

Request:

Calibration / geometry / test reports
Maintenance / service logs (spindle rebuilds, axis servicing)
CNC parameter backups, compensation tables, calibration offsets
Electrical & hydraulic / pneumatic wiring diagrams
Parts list (dressers, spindle parts, encoders)
Operator / maintenance manuals
History of crashes, modifications, or retrofits

11) Acceptance Criteria & Benchmark Targets

Here is a sample target table (adjust per the exact model’s spec sheet):

Parameter	Target / Tolerance	Notes
Linear axis accuracy (X, Y, Z)	± 5 µm or better	As per Campbell catalog
Angular indexing error (B, C axes)	≤ 5–10 arc seconds	Campbell lists 10 arc second for B / C in catalog
Spindle runout (radial / axial)	≤ 5 µm / better	At test bar or gauge
Backlash / reversal error	≤ 0.01 mm	Or as per spec sheet
Repeatability	± 3 µm or better	Over multiple cycles
Thermal drift over 1 hr	≤ 5 µm	Under stable thermal conditions
Dresser repeatability	≤ 5 µm motion consistency	Dressing cycles should be repeatable
Spindle vibration / noise levels	Low, no bearing whine	Use analyzer
Control system stability / no recurring alarms	Alarms should be rare	Healthy control logs