How to inspect a used CNC machine before you buy

A used machine is a bet on how it was run and maintained. A careful inspection turns that bet into a decision you can defend. If you can't attend in person, send someone who can, or ask the seller for the video evidence described below.

1. See it run

Start with the machine powered up and cutting, not sitting cold. A machine that has been standing can look fine and fail the moment it works.

• Power it up from cold and watch the start-up sequence. Note any alarms and how long they take to clear.
• Run the warm-up routine, then run a real program: rapids, a tool change cycle, and a cut if the seller can set one up.
• Listen. Rumbling, whining or knocking from the spindle, axes or tool changer is information. Record it on your phone.
• Treat a refusal to power the machine up as a reason to pause, not a detail to wave through.

2. Hours and history

Ask for spindle hours, power-on hours and tool-change count if the control records them. Treat the numbers as a clue, not proof: counters can be reset, and a battery failure or software change can wipe them. Check what the numbers say against the machine's age and the wear you can see.

• Ask for maintenance records and any major repairs (spindle, ballscrews, control boards).
• Ask what the machine made and for whom. A machine from a clean, climate-controlled shop is a different bet from one that cut abrasive material for years.
• Ask about crash history. A crashed machine can look fine and still be out of alignment.
• Check the control's alarm history if it keeps one.

3. Spindle and taper

• Run the spindle through its full speed range and listen for noise and vibration at every step.
• Check the spindle taper for scoring, fretting or damage, and check the drawbar clamp and unclamp.
• Measure runout with a test bar and a dial indicator at the nose and again about 10 inches out. Ask the seller if you can; if not, a third-party bar test is worth paying for on a big purchase.
• Look for coolant in places it shouldn't be, such as the spindle housing.
• If the machine has a spindle chiller, confirm that it runs and holds temperature.

4. Axes: ways, ballscrews and backlash

• Look at the ways. Coolant stains are normal. Scoring, galling, rust pits and worn-through paint are not. Wipe a section clean and check the surface.
• Feel for backlash. Mount a dial indicator and reverse each axis. Large readings, or readings that vary along the travel, point to worn ballscrews or nuts.
• Check lash compensation parameters. High compensation values can mask wear.
• Move every axis through its full travel at low and high speed. It should be smooth, with no hesitation, binding or noise at the ends.
• Check the way covers and wipers. Damaged covers let chips in and shorten life.

5. Tool changer

• Cycle the changer through every pocket, forwards and backwards, several times.
• Watch for hesitation, hard bumps or dropped tools.
• Confirm the tool capacity matches the listing and that every pocket works.
• Check the tool clamp and unclamp and the air supply that drives them.
• Listen to the changer door and arm or carousel mechanism for wear.

6. Control and electrical

On an older machine, the control is often the real age of the machine. Check it as carefully as the iron.

• Check the screen, keyboard, handwheel and buttons. Replacement parts for older controls can be hard to find.
• Find out the control model and version and whether support, parts and repair are available for it.
• Ask when the backup battery was last replaced, and have parameters, offsets and programs backed up before the machine moves.
• Confirm the electrical requirement: voltage, phase and kVA. Many used machines need a transformer or a phase converter in your building.
• Check the electrical cabinet for burned smell, heat damage, loose wiring and clean filters.

7. Coolant, lube, air and chips

• Run the coolant system, including through-spindle coolant if fitted, and check pressure.
• Check way lube reservoir level and that oil reaches the ways.
• Check compressed-air pressure and fittings for leaks.
• Run the chip conveyor or auger and check its guards and doors.
• Check the machine's guarding and interlocks. Safety features that have been defeated are a red flag.

8. Paperwork and terms

• Match the nameplate serial number to the paperwork.
• Get manuals and ask what comes with the machine: tooling, vises, rotary table, probe, spare parts. Compare against the listing's included-items list.
• Ask whether the seller owns the machine free and clear. Read how to avoid used machinery scams for lien checks and payment safety.
• Get terms in writing: price, what's included, who loads, who ships, who insures, and whether the sale is as-is or carries any return or warranty.
• Plan the move: weight, dimensions and the equipment needed. See the rigging and shipping guide.

Quick-reference table

Look at some real listings

Every machine we list shows its specifications and the items included with it, so you can compare them against this checklist: 2016 Haas VF-5/50XT, 2001 Mori Seiki SV-503B, 1997 Haas VF-4, and the full vertical machining center inventory.