Used CNC Machine: Pre-Purchase Inspection Checklist

Guarding and control support decide whether a used CNC is a bargain or a boat anchor. Ticks save on this device; print it for the inspection.

Safety & guarding (federal requirement, not a nicety)

Door interlock: command a spindle start with the door open — it must refuse (a bypassed interlock is your cost, not a discount)
Every e-stop drops the machine, tested in a dry run
Enclosure windows and panels present and intact
On a lathe, the chuck guard and its interlock are present and working
The machine can be locked out (disconnect present, lockable, reachable)

The control (the obsolescence trap)

Identify the control make and version, and confirm the maker still supports it (an orphaned control can cost more to retrofit than the machine is worth)
Power it up and run a program — confirm the control boots and axes home

Mechanical accuracy

Measure spindle taper runout cold, then again after a full warm-up cycle; get both numbers in writing
Check each axis for ball-screw backlash / lost motion
Ask whether the air supply had a dryer, and whether the spindle was ever greased (it should not be)

Install & deal math

Confirm you have the 3-phase power the machine needs, and a plan to anchor it (a fixed machine must be securely anchored)
Budget rigging and freight for a multi-ton machine
Compare the ask to the model’s observed used range and spindle-repair exposure

A working checklist, not legal or professional advice. See the full guide for the reasoning behind each step, and the model records for prices and known failures.