This could be a very long and detailed discussion. But in the interest of time the major
items would be, once you determine the size (based on the parts that you produce) and
which manufacturers you would be happy with and budget:

1. Condition

a.) Start with visual. You can get a feel for how a machine is used by its physical condition. Some wear and tear is normal, but excessive wear should be questioned.

b.) How does it sound? The spindle, the axis motors. All should be quiet. Most guys recognize a spindle with a high pitch sound. It could mean bad bearings.

c.) Do all components work? Run the tool changer, the chip auger or conveyor, the programmable coolant nozzle (on a Haas).

d.) A more extensive inspection can be done by a hired technician. While it may cost a few hundred dollars you could save costs by hiring an independent technician rather than pay the rates of a distributorship. If the machine is too far to see in person without paying for air fare, the cost to hire someone might be justified.

2. Age

A machine that is too old may have old technology. This could mean as little as it doesn’t perform to the current standards (processing time, rapids, etc.). But it could also mean that parts aren’t supported. Processing boards and amplifiers on machines 20 years and older sometimes get discontinued. They
may still be able to get repaired but it gets harder as the machine gets older.

3. Materials Ran

Most machines will be used cutting steel or aluminum. I’ve seen some that cut just plastic. But the ones that have been used to cut castings or graphite can prematurely wear a machine.

4. Hours

Some manufacturers have hour meters on the machines, giving you a good idea of the overall use and wear of a machine. *Rule of thumb – a spindle should average 1000 hours per year in a shop running 1 shift. But be careful. In a Haas, for example there are two screens with time on them. One is easily reset. It is meant to be, just like a trip odometer on a car. It is designed to be used to see how long a job runs. The second screen is only found by debugging the control. That has the true spindle hours on it. But it too can be reset if certain boards are replaced, so even those numbers are not correct on 100% of the machines out there.