Used CNC Machine Inspection Checklist
A comprehensive inspection checklist for evaluating used CNC machines—vertical machining centers, horizontal machining centers, and CNC lathes. Know what to look for before you buy.
Before You Inspect: Key Tips
- •Always run the machine under power—preferably making cuts
- •Ask for spindle hours—this is the most important wear metric
- •Check alarm history on the control for hidden problems
- •Bring a dial indicator to check spindle runout and backlash
- •Listen for unusual noises—they often indicate problems
- •Consider a professional inspection for expensive machines
Typical Repair/Replacement Costs
Understanding repair costs helps you evaluate machines and negotiate pricing:
| Component | Typical Cost Range | Notes |
|---|---|---|
| Spindle Rebuild | $5,000 - $25,000+ | Depends on spindle size and speed; most expensive component |
| Ball Screw Replacement | $2,000 - $10,000/axis | Includes ball screw, nut, and labor |
| Servo Motor | $1,500 - $5,000 | Exchange or rebuild; varies by brand |
| Servo Drive | $2,000 - $8,000 | May be available rebuilt |
| Linear Guide Rails | $1,500 - $5,000/axis | Plus labor for alignment |
| Tool Changer Repair | $500 - $5,000 | Depends on type and problem |
| Control Board/Power Supply | $1,000 - $10,000 | Varies widely by control type |
Note: These are general ranges for market estimates. Actual costs vary by machine brand, size, and local labor rates.
1. Documentation & Records
2. Spindle System
3. Axis Motion Systems
4. Control System
5. Tool Changer (VMC/HMC)
6. Turret/Tool Post (Lathes)
7. Electrical & Safety
8. Operational Test
Ball Screw Backlash Reference
| Condition | Backlash (inches) | Action |
|---|---|---|
| New / Excellent | < 0.0003" | No action needed |
| Good | 0.0003" - 0.0007" | Normal wear; acceptable for most work |
| Worn | 0.0007" - 0.0015" | May affect accuracy; budget for replacement |
| Excessive | > 0.0015" | Needs replacement; negotiate price accordingly |
Note: Backlash specifications vary by manufacturer and machine class. High-precision machines have tighter specs than production machines. Consult OEM specifications.
Red Flags to Watch For
Spindle Issues
- • Grinding or rumbling noise at speed
- • Runout greater than 0.0003"
- • Visible damage to spindle nose
- • Excessive heat during operation
- • Vibration at certain RPM ranges
Motion System Issues
- • Backlash exceeding 0.001"
- • Sticking or binding during movement
- • Scoring on ways or linear guides
- • Unusual servo motor noise
- • Inconsistent positioning
Control System Issues
- • Recurring alarms in history
- • Corrupted or missing parameters
- • Non-functional screens
- • Communication port failures
- • Very old software with no updates
General Concerns
- • Evidence of crash damage
- • No maintenance records
- • Machine sitting unpowered long time
- • Seller reluctant to run machine
- • Coolant contamination in way oil
Frequently Asked Questions
What are the most important things to check on a used CNC machine?
The three most critical areas are: 1) Spindle condition - affects surface finish, tool life, and accuracy, 2) Ball screws and linear guides - determines positioning accuracy and repeatability, 3) Control system - affects capability, programming, and future support. These directly impact machine performance and rebuild costs.
How do I check spindle condition on a used CNC machine?
Check spindle hours (many machines track this), listen for bearing noise at various speeds, check for runout with a test indicator, feel for vibration, and look for signs of crash damage or overheating. Request spindle documentation if available. Spindle rebuilds are expensive—$5,000 to $25,000+ depending on size and type.
What does ball screw backlash tell me about machine condition?
Ball screw backlash indicates wear in the positioning system. New machines typically have 0.0002-0.0005" backlash. Values over 0.001" may affect accuracy and may require ball screw replacement ($2,000-$10,000+ per axis depending on machine size). Check all axes and compare to manufacturer specifications.
Should I run test cuts when inspecting a used CNC machine?
Yes, if possible. Running actual test cuts reveals real-world performance. Use a circle-diamond-square test piece for mills, or turn a test bar for lathes. Measure resulting parts for accuracy, surface finish, and repeatability. This is the most reliable way to evaluate machine capability.
How important are spindle hours on a used CNC machine?
Spindle hours are one of the most important metrics. Most industrial spindles are rated for 10,000-20,000 hours depending on use patterns. A machine with 3,000 hours is considerably different from one with 15,000 hours. However, maintenance history and usage type matter too—high-speed finishing wear differs from heavy hogging.
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