If you check only one thing on a used CNC machine, check the spindle. It is the heart of the machine — it holds the tool and drives the cut — and it is the single most expensive thing to get wrong. A spindle rebuild runs $8,000–$30,000, enough to wipe out the savings on a used purchase and then some. The good news: a structured inspection takes fifteen minutes and tells you almost everything.
Why the spindle matters most
Every other worn component on a CNC — ways, ballscrews, tooling — is repairable at manageable cost. A worn spindle is different: it degrades your accuracy on every part and its rebuild cost can dwarf the price of the machine. Inspect it first, and let what you find set the price.