Second hand CNC machines: 6 checks before you commit

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  Key takeaways
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  Used machine versus outside machining
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  Why second hand CNC machines look cheaper than they are
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  What to inspect on a used CNC machine before you pay
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  Control, spares and service: the quiet deal breaker
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  When second hand CNC machines are the wrong answer
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  Step by step: how to qualify a used machine

The sticker price is the smallest number in the deal. A used vertical mill at 5,000 kg needs rigging, a low-bed trailer, a crane and a concrete pad rated for the load. Add a transformer if your supply is not matched, plus air, coolant and chip handling. That package often runs 20–40% of the purchase price, and it lands before the first part is cut.

Then comes the first breakdown. A spindle rebuild or a ball screw replacement on a discontinued model can take weeks and cost more than the machine was worth. Ask the seller for the last three years of service records. If they cannot produce them, price the machine as if the spindle is already tired.

Hourly cost is the number that decides. A used machine running 2,000 hours a year spreads its purchase and repair cost over real output. The same machine running 200 hours a year carries a heavy idle cost, and idle machines still leak money through floor space and maintenance.

Do not compare a used machine against a new one alone. Compare it against the quote you would get from an outside shop for the same parts. That is the only baseline that tells you whether ownership pays.

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  Rigging and foundationCrane, transport, pad and levelling are never optional.
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  Power and airCheck voltage, phase and air volume before you sign.
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  ToolingHolders, collets and fixturing can cost as much as the machine.
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  First-year repairsSet aside a reserve; worn machines fail early.

Start with geometry, not the control. Put a dial indicator on the table and sweep a 300 mm circle with a test bar in the spindle. Squareness error shows up as a mismatch between the X and Y readings. Ask for the number, not a verbal assurance. If the machine cannot cut a circle within 0.02 mm, no controller upgrade will save it.

Check backlash on each axis by approaching a position from both directions and reading the difference. On a healthy machine this is usually under 0.01 mm after compensation. Anything larger points to worn thrust bearings or a tired ball screw.

Spindle condition is the expensive one. Listen at full speed with no load, then run a warm-up cycle for 30 minutes and check for growth. Ask for a taper contact check with blueing. A taper that shows less than about 80% contact will not hold tool concentricity on finishing passes.

Ways and rails come next. On box ways, look for scoring and check oil flow at every metering point. On linear rails, check for brinelling and listen for rumble during rapid moves. Then run a test part and measure it against the drawing before you commit.

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  Circle and square test300 mm sweep, compare X and Y readings.
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  Backlash checkApproach from both sides, expect under 0.01 mm.
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  Spindle warm-up30 minutes, watch thermal growth and noise.
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  Test cutMeasure the part, do not trust a video.

A Fanuc or Siemens control with a wide installed base is easier to keep alive. Parts are stocked, forums exist, and local engineers know the ladder. A discontinued or obscure control turns every fault into a research project. If the seller cannot name the control model and its year, walk away.

Ask where the nearest service engineer sits and how long a call-out takes. If the answer is a flight, the machine needs a spare-parts kit on site: a drive, an encoder, a servo amplifier and the parameters backed up on a USB stick. Parameter loss on an old control can stop the machine for days.

Consumables matter too. Tool holders with a standard taper are cheap and available. A proprietary interface locks you into one supplier. Check the tool changer carousel for worn fingers and confirm the magazine count matches the work you plan to run.

Finally, check the paperwork. A machine with a maintenance log, a recent calibration and a clean electrical cabinet is a different asset from one with a fresh coat of paint over a leaking gearbox.

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  Wide-installed controlFanuc or Siemens parts are easier to source.
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  Local engineer distanceDrive time decides your downtime.
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  Spares on the shelfKeep a drive, encoder and parameter backup.
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  Standard tooling interfaceAvoid proprietary tapers and holders.

Ownership adds work that never appears on a quote: programming, fixturing, tool setting, coolant changes, chip removal and inspection. On a two-person team, that time comes out of billable hours. If your parts change every few weeks, the setup burden eats the saving.

Precision is the other limit. Used machines can hold ±0.005 mm if the geometry is sound and the spindle is fresh, but proving that takes a documented test cut. Without it, you are buying a promise. For medical or aerospace work with traceability requirements, the inspection and documentation load usually belongs with a supplier who already runs it daily.

Volume changes the math. One prototype to 10,000+ part runs sit at opposite ends of the same decision. Below a few hundred parts a year, an outside shop wins on cost per part and on time to first article. Above that, with a stable part family and steady demand, ownership starts to pay.

There is a middle path. Keep a used machine for soft material and simple geometry, and send hard material, tight tolerance and finishing work out. That split keeps the capital low without carrying the risk of every demanding job.

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  Unstable part mixHigh setup hours kill the saving.
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  Traceable workCertificates and reports belong with a certified shop.
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  Low annual volumeCost per part stays high on idle iron.
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  Hybrid splitOwn the easy work, outsource the hard work.