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Advice on buying a used CNC machine tool

Tips on Buying used.

You should ask to see the Spindle time, but remember that the hours on Fanuc controls can be reset.  

Make sure someone there can run the CNC (someone that knows the control) to test all the functions you know you will be using on your parts (live tooling, tool-change, spindle orientation, chip conveyor, etc, etc) See below for a quick inspections list.

Ask what company they bought the machine from. If its from a big company, there is a good chance that they ran the machine 24/7.

Most CNCmachines have a Data Sheet in the back panel with all the options it came with. make sure this sheet has the same serial # as the machine. most manufactures will give you lots of information (to whom it was originally sold to) on the machine if you give them the serial #. You should get a serial # also to check if the dealer you are buying the machine from is the actual owner of the machine and not brokering the machine.

If the machine is older, make sure you get as many manuals as possible (Parts, Maintenance, Programing, Electrical, LADDER!!!) If the machine is really old, ask if they have tool holders as well.

Thanks to Marcos for contributing the information above.

Its always a good idea to have a qualified service rep to check the machine over, but go through this list yourself first to make sure he doesn't forget anything of great importance. The below doesn't take in consideration of alignments or tolerance issues. This is only a quick guide that anyone can do.

Quick inspection for anyone to perform-

First thing you should do is ask to see the service records/reports from when the techs were in. This can give you a good idea about how well it was maintained as well as identify on going problems that you may inherit if you buy the machine.

  1. Hold your hand on all the axes X,Y,Z etc. and move them. Keep your hand on the casting and put in rapid mode 50 percent and move them. Feel to see if it transitions smoothly, also check at a stopped position to see if there's some oscillation. If possible grab onto ballscrew at stopped position to fell for this oscillation after moving a little bit. Listen for low growl or any abnormal noise when moving in rapid. This could mean there's either bad bearings, ballscrew, worn ways and even possibly little or no turkite left. Listen to each of the servo motors for a high pitch humming. This could mean there are some problems as well.

  2. Check the spindle. Run the spindle at multiple RPMS (50,100,1000,5000,Max). Ask to come listen when its quieter in the shop (lunch).

  3. Ask them to put a rapid program in machine and run full stroke in all axes. Listen for Low Growl possibly bad bearings, ballscrew etc.

  4. Inspect ways or linear guides. Look to see if it has grooves or pitted. Could mean turkite gone or improper lubrication currently or some time ago. Possible BIGGG Problems make sure to get professional opinion if still considering. It can be difficult to access these areas and can take a lot of time. If its turkite you have to completely remove the axis and look at it. There are other ways to try to determine but they are not usually 100 percent accurate. If linear guides again look for pitting, discoloration or browning of the grooves along the entire length of the guide.

  5. Perform pallet change and tool change. Listen for any abnormal noise. Look at the tool change fingers for wear and alignment problems.

  6. What material are they cutting If its Cast iron- I would say run away, but if you don't, heres what to expect. It gets into everything and and turns into a solid rusted mass which you need a chisel and hammer literally to chip away. It can cause a lot of coolant drainage areas to plug up, for example backing up coolant into bearings, guides, motor, switches etc. It also works its way under way wipers, waycovers and more and acts like an abrasive.

  7. Lathe-Is the metal around the tool posts or the mounting surface of a holder distorted Run an indicator on a few pockets to see how straight they are. You may see a gradual incline or decline which tells you its out of alignment, which is only an alignment problem. The important thing is to make sure its gradual and there are no high spots and also to make sure all of the turret stations are the same. If the pockets are distorted then you will have problems keeping your drills on center and other tooling.

Buying used CNC advice help